-finish implementation of protocol v16, still undertested

20 files changed, 805 insertions, 367 deletions

diff --git a/src/backend/taler-merchant-httpd_config.c b/src/backend/taler-merchant-httpd_config.c
index 97dd1714..10f0cd39 100644
--- a/src/backend/taler-merchant-httpd_config.c
+++ b/src/backend/taler-merchant-httpd_config.c
@@ -42,7 +42,7 @@
  * #MERCHANT_PROTOCOL_CURRENT and #MERCHANT_PROTOCOL_AGE in
  * merchant_api_config.c!
  */
-#define MERCHANT_PROTOCOL_VERSION "15:0:11"
+#define MERCHANT_PROTOCOL_VERSION "16:0:12"
 
 
 /**
diff --git a/src/backend/taler-merchant-httpd_private-delete-products-ID.c b/src/backend/taler-merchant-httpd_private-delete-products-ID.c
index 7d314785..23b6de3c 100644
--- a/src/backend/taler-merchant-httpd_private-delete-products-ID.c
+++ b/src/backend/taler-merchant-httpd_private-delete-products-ID.c
@@ -59,22 +59,30 @@ TMH_private_delete_products_ID (const struct TMH_RequestHandler *rh,
                                        TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE,
                                        "delete_product (soft)");
   case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
-    /* check if deletion must have failed because of locks by
-       checking if the product exists */
-    qs = TMH_db->lookup_product (TMH_db->cls,
-                                 mi->settings.id,
-                                 hc->infix,
-                                 NULL);
-    if (GNUNET_DB_STATUS_HARD_ERROR == qs)
-      return TALER_MHD_reply_with_error (connection,
-                                         MHD_HTTP_INTERNAL_SERVER_ERROR,
-                                         TALER_EC_GENERIC_DB_STORE_FAILED,
-                                         "lookup_product");
-    if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
-      return TALER_MHD_reply_with_error (connection,
-                                         MHD_HTTP_NOT_FOUND,
-                                         TALER_EC_MERCHANT_GENERIC_PRODUCT_UNKNOWN,
-                                         hc->infix);
+    {
+      size_t num_categories = 0;
+      uint64_t *categories = NULL;
+
+      /* check if deletion must have failed because of locks by
+         checking if the product exists */
+      qs = TMH_db->lookup_product (TMH_db->cls,
+                                   mi->settings.id,
+                                   hc->infix,
+                                   NULL,
+                                   &num_categories,
+                                   &categories);
+      if (GNUNET_DB_STATUS_HARD_ERROR == qs)
+        return TALER_MHD_reply_with_error (connection,
+                                           MHD_HTTP_INTERNAL_SERVER_ERROR,
+                                           TALER_EC_GENERIC_DB_STORE_FAILED,
+                                           "lookup_product");
+      if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
+        return TALER_MHD_reply_with_error (connection,
+                                           MHD_HTTP_NOT_FOUND,
+                                           TALER_EC_MERCHANT_GENERIC_PRODUCT_UNKNOWN,
+                                           hc->infix);
+      GNUNET_free (categories);
+    }
     return TALER_MHD_reply_with_error (
       connection,
       MHD_HTTP_CONFLICT,
diff --git a/src/backend/taler-merchant-httpd_private-get-pos.c b/src/backend/taler-merchant-httpd_private-get-pos.c
index 681b90c4..4c14b6ae 100644
--- a/src/backend/taler-merchant-httpd_private-get-pos.c
+++ b/src/backend/taler-merchant-httpd_private-get-pos.c
@@ -50,18 +50,21 @@ static void
 add_product (void *cls,
              uint64_t product_serial,
              const char *product_id,
-             const struct TALER_MERCHANTDB_ProductDetails *pd)
+             const struct TALER_MERCHANTDB_ProductDetails *pd,
+             size_t num_categories,
+             const uint64_t *categories)
 {
   struct Context *ctx = cls;
   json_t *pa = ctx->pa;
   json_t *cata;
 
-  /* FIXME-8839: add proper category support! */
   cata = json_array ();
-  GNUNET_assert (
-    0 == json_array_append_new (
-      cata,
-      json_integer (0)));
+  GNUNET_assert (NULL != cata);
+  for (size_t i = 0; i<num_categories; i++)
+    GNUNET_assert (
+      0 == json_array_append_new (
+        cata,
+        json_integer (categories[i])));
   GNUNET_assert (
     0 ==
     json_array_append_new (
diff --git a/src/backend/taler-merchant-httpd_private-get-products-ID.c b/src/backend/taler-merchant-httpd_private-get-products-ID.c
index 107081f7..0729b1df 100644
--- a/src/backend/taler-merchant-httpd_private-get-products-ID.c
+++ b/src/backend/taler-merchant-httpd_private-get-products-ID.c
@@ -40,12 +40,17 @@ TMH_private_get_products_ID (
   struct TMH_MerchantInstance *mi = hc->instance;
   struct TALER_MERCHANTDB_ProductDetails pd = { 0 };
   enum GNUNET_DB_QueryStatus qs;
+  size_t num_categories = 0;
+  uint64_t *categories = NULL;
+  json_t *jcategories;
 
   GNUNET_assert (NULL != mi);
   qs = TMH_db->lookup_product (TMH_db->cls,
                                mi->settings.id,
                                hc->infix,
-                               &pd);
+                               &pd,
+                               &num_categories,
+                               &categories);
   if (0 > qs)
   {
     GNUNET_break (0);
@@ -61,6 +66,16 @@ TMH_private_get_products_ID (
                                        TALER_EC_MERCHANT_GENERIC_PRODUCT_UNKNOWN,
                                        hc->infix);
   }
+  jcategories = json_array ();
+  GNUNET_assert (NULL != jcategories);
+  for (size_t i = 0; i<num_categories; i++)
+  {
+    GNUNET_assert (0 ==
+                   json_array_append_new (jcategories,
+                                          json_integer (categories[i])));
+  }
+  GNUNET_free (categories);
+
   {
     MHD_RESULT ret;
 
@@ -73,6 +88,8 @@ TMH_private_get_products_ID (
                                      pd.description_i18n),
       GNUNET_JSON_pack_string ("unit",
                                pd.unit),
+      GNUNET_JSON_pack_array_steal ("categories",
+                                    jcategories),
       TALER_JSON_pack_amount ("price",
                               &pd.price),
       GNUNET_JSON_pack_allow_null (
diff --git a/src/backend/taler-merchant-httpd_private-patch-products-ID.c b/src/backend/taler-merchant-httpd_private-patch-products-ID.c
index 7bc327cd..6e50cced 100644
--- a/src/backend/taler-merchant-httpd_private-patch-products-ID.c
+++ b/src/backend/taler-merchant-httpd_private-patch-products-ID.c
@@ -1,6 +1,6 @@
 /*
   This file is part of TALER
-  (C) 2020 Taler Systems SA
+  (C) 2020-2024 Taler Systems SA
 
   TALER is free software; you can redistribute it and/or modify
   it under the terms of the GNU Affero General Public License as
@@ -29,76 +29,6 @@
 
 
 /**
- * How often do we retry the simple INSERT database transaction?
- */
-#define MAX_RETRIES 3
-
-
-/**
- * Determine the cause of the PATCH failure in more detail and report.
- *
- * @param connection connection to report on
- * @param instance_id instance we are processing
- * @param product_id ID of the product to patch
- * @param pd product details we failed to set
- */
-static MHD_RESULT
-determine_cause (struct MHD_Connection *connection,
-                 const char *instance_id,
-                 const char *product_id,
-                 const struct TALER_MERCHANTDB_ProductDetails *pd)
-{
-  struct TALER_MERCHANTDB_ProductDetails pdx;
-  enum GNUNET_DB_QueryStatus qs;
-
-  qs = TMH_db->lookup_product (TMH_db->cls,
-                               instance_id,
-                               product_id,
-                               &pdx);
-  switch (qs)
-  {
-  case GNUNET_DB_STATUS_HARD_ERROR:
-    GNUNET_break (0);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_INTERNAL_SERVER_ERROR,
-                                       TALER_EC_GENERIC_DB_FETCH_FAILED,
-                                       NULL);
-  case GNUNET_DB_STATUS_SOFT_ERROR:
-    GNUNET_break (0);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_INTERNAL_SERVER_ERROR,
-                                       TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE,
-                                       "unexpected serialization problem");
-  case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_NOT_FOUND,
-                                       TALER_EC_MERCHANT_GENERIC_PRODUCT_UNKNOWN,
-                                       product_id);
-  case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
-    break; /* do below */
-  }
-
-  {
-    enum TALER_ErrorCode ec;
-
-    ec = TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE;
-    if (pdx.total_lost > pd->total_lost)
-      ec = TALER_EC_MERCHANT_PRIVATE_PATCH_PRODUCTS_TOTAL_LOST_REDUCED;
-    if (pdx.total_sold > pd->total_sold)
-      ec = TALER_EC_MERCHANT_PRIVATE_PATCH_PRODUCTS_TOTAL_SOLD_REDUCED;
-    if (pdx.total_stock > pd->total_stock)
-      ec = TALER_EC_MERCHANT_PRIVATE_PATCH_PRODUCTS_TOTAL_STOCKED_REDUCED;
-    TALER_MERCHANTDB_product_details_free (&pdx);
-    GNUNET_break (TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE != ec);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_CONFLICT,
-                                       ec,
-                                       NULL);
-  }
-}
-
-
-/**
  * PATCH configuration of an existing instance, given its configuration.
  *
  * @param rh context of the handler
@@ -107,13 +37,15 @@ determine_cause (struct MHD_Connection *connection,
  * @return MHD result code
  */
 MHD_RESULT
-TMH_private_patch_products_ID (const struct TMH_RequestHandler *rh,
-                               struct MHD_Connection *connection,
-                               struct TMH_HandlerContext *hc)
+TMH_private_patch_products_ID (
+  const struct TMH_RequestHandler *rh,
+  struct MHD_Connection *connection,
+  struct TMH_HandlerContext *hc)
 {
   struct TMH_MerchantInstance *mi = hc->instance;
   const char *product_id = hc->infix;
   struct TALER_MERCHANTDB_ProductDetails pd = {0};
+  const json_t *categories = NULL;
   int64_t total_stock;
   enum GNUNET_DB_QueryStatus qs;
   struct GNUNET_JSON_Specification spec[] = {
@@ -135,6 +67,10 @@ TMH_private_patch_products_ID (const struct TMH_RequestHandler *rh,
       GNUNET_JSON_spec_json ("taxes",
                              &pd.taxes),
       NULL),
+    GNUNET_JSON_spec_mark_optional (
+      GNUNET_JSON_spec_array_const ("categories",
+                                    &categories),
+      NULL),
     GNUNET_JSON_spec_int64 ("total_stock",
                             &total_stock),
     GNUNET_JSON_spec_mark_optional (
@@ -155,6 +91,15 @@ TMH_private_patch_products_ID (const struct TMH_RequestHandler *rh,
       NULL),
     GNUNET_JSON_spec_end ()
   };
+  MHD_RESULT ret;
+  size_t num_cats = 0;
+  uint64_t *cats = NULL;
+  bool no_instance;
+  ssize_t no_cat;
+  bool no_product;
+  bool lost_reduced;
+  bool sold_reduced;
+  bool stock_reduced;
 
   pd.total_sold = 0; /* will be ignored anyway */
   GNUNET_assert (NULL != mi);
@@ -173,11 +118,11 @@ TMH_private_patch_products_ID (const struct TMH_RequestHandler *rh,
   if (total_stock < -1)
   {
     GNUNET_break_op (0);
-    GNUNET_JSON_parse_free (spec);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_BAD_REQUEST,
-                                       TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                                       "total_stock");
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_BAD_REQUEST,
+                                      TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                                      "total_stock");
+    goto cleanup;
   }
   if (-1 == total_stock)
     pd.total_stock = INT64_MAX;
@@ -189,23 +134,45 @@ TMH_private_patch_products_ID (const struct TMH_RequestHandler *rh,
   if (! TMH_location_object_valid (pd.address))
   {
     GNUNET_break_op (0);
-    GNUNET_JSON_parse_free (spec);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_BAD_REQUEST,
-                                       TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                                       "address");
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_BAD_REQUEST,
+                                      TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                                      "address");
+    goto cleanup;
+  }
+  num_cats = json_array_size (categories);
+  cats = GNUNET_new_array (num_cats,
+                           uint64_t);
+  {
+    size_t idx;
+    json_t *val;
+
+    json_array_foreach (categories, idx, val)
+    {
+      if (! json_is_integer (val))
+      {
+        GNUNET_break_op (0);
+        ret = TALER_MHD_reply_with_error (connection,
+                                          MHD_HTTP_BAD_REQUEST,
+                                          TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                                          "categories");
+        goto cleanup;
+      }
+      cats[idx] = json_integer_value (val);
+    }
   }
+
   if (NULL == pd.description_i18n)
     pd.description_i18n = json_object ();
 
   if (! TALER_JSON_check_i18n (pd.description_i18n))
   {
     GNUNET_break_op (0);
-    GNUNET_JSON_parse_free (spec);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_BAD_REQUEST,
-                                       TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                                       "description_i18n");
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_BAD_REQUEST,
+                                      TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                                      "description_i18n");
+    goto cleanup;
   }
 
   if (NULL == pd.taxes)
@@ -214,74 +181,143 @@ TMH_private_patch_products_ID (const struct TMH_RequestHandler *rh,
   if (! TMH_taxes_array_valid (pd.taxes))
   {
     GNUNET_break_op (0);
-    GNUNET_JSON_parse_free (spec);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_BAD_REQUEST,
-                                       TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                                       "taxes");
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_BAD_REQUEST,
+                                      TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                                      "taxes");
+    goto cleanup;
   }
+
   if (NULL == pd.image)
     pd.image = "";
   if (! TMH_image_data_url_valid (pd.image))
   {
     GNUNET_break_op (0);
-    GNUNET_JSON_parse_free (spec);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_BAD_REQUEST,
-                                       TALER_EC_GENERIC_PARAMETER_MALFORMED,
-                                       "image");
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_BAD_REQUEST,
+                                      TALER_EC_GENERIC_PARAMETER_MALFORMED,
+                                      "image");
+    goto cleanup;
   }
+
   if ( (pd.total_stock < pd.total_sold + pd.total_lost) ||
        (pd.total_sold + pd.total_lost < pd.total_sold) /* integer overflow */)
   {
     GNUNET_break_op (0);
-    GNUNET_JSON_parse_free (spec);
-    return TALER_MHD_reply_with_error (
+    ret = TALER_MHD_reply_with_error (
       connection,
       MHD_HTTP_BAD_REQUEST,
       TALER_EC_MERCHANT_PRIVATE_PATCH_PRODUCTS_TOTAL_LOST_EXCEEDS_STOCKS,
       NULL);
+    goto cleanup;
   }
+
   qs = TMH_db->update_product (TMH_db->cls,
                                mi->settings.id,
                                product_id,
-                               &pd);
+                               &pd,
+                               num_cats,
+                               cats,
+                               &no_instance,
+                               &no_cat,
+                               &no_product,
+                               &lost_reduced,
+                               &sold_reduced,
+                               &stock_reduced);
+  switch (qs)
   {
-    MHD_RESULT ret = MHD_NO;
+  case GNUNET_DB_STATUS_HARD_ERROR:
+    GNUNET_break (0);
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_INTERNAL_SERVER_ERROR,
+                                      TALER_EC_GENERIC_DB_STORE_FAILED,
+                                      NULL);
+    goto cleanup;
+  case GNUNET_DB_STATUS_SOFT_ERROR:
+    GNUNET_break (0);
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_INTERNAL_SERVER_ERROR,
+                                      TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE,
+                                      "unexpected serialization problem");
+    goto cleanup;
+  case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
+    GNUNET_break (0);
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_INTERNAL_SERVER_ERROR,
+                                      TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE,
+                                      "unexpected problem in stored procedure");
+    goto cleanup;
+  case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
+    break;
+  }
 
-    switch (qs)
-    {
-    case GNUNET_DB_STATUS_HARD_ERROR:
-      GNUNET_break (0);
-      ret = TALER_MHD_reply_with_error (connection,
-                                        MHD_HTTP_INTERNAL_SERVER_ERROR,
-                                        TALER_EC_GENERIC_DB_STORE_FAILED,
-                                        NULL);
-      break;
-    case GNUNET_DB_STATUS_SOFT_ERROR:
-      GNUNET_break (0);
-      ret = TALER_MHD_reply_with_error (connection,
-                                        MHD_HTTP_INTERNAL_SERVER_ERROR,
-                                        TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE,
-                                        "unexpected serialization problem");
-      break;
-    case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
-      ret = determine_cause (connection,
-                             mi->settings.id,
-                             product_id,
-                             &pd);
-      break;
-    case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
-      ret = TALER_MHD_reply_static (connection,
-                                    MHD_HTTP_NO_CONTENT,
-                                    NULL,
-                                    NULL,
-                                    0);
-      break;
-    }
-    GNUNET_JSON_parse_free (spec);
-    return ret;
+  if (no_instance)
+  {
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_NOT_FOUND,
+                                      TALER_EC_MERCHANT_GENERIC_INSTANCE_UNKNOWN,
+                                      mi->settings.id);
+    goto cleanup;
+  }
+  if (-1 != no_cat)
+  {
+    char cats[24];
+
+    GNUNET_snprintf (cats,
+                     sizeof (cats),
+                     "%llu",
+                     (unsigned long long) no_cat);
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_NOT_FOUND,
+                                      TALER_EC_MERCHANT_GENERIC_CATEGORY_UNKNOWN,
+                                      cats);
+    goto cleanup;
+  }
+  if (no_product)
+  {
+    ret = TALER_MHD_reply_with_error (connection,
+                                      MHD_HTTP_NOT_FOUND,
+                                      TALER_EC_MERCHANT_GENERIC_PRODUCT_UNKNOWN,
+                                      product_id);
+    goto cleanup;
+  }
+  if (lost_reduced)
+  {
+    ret = TALER_MHD_reply_with_error (
+      connection,
+      MHD_HTTP_CONFLICT,
+      TALER_EC_MERCHANT_PRIVATE_PATCH_PRODUCTS_TOTAL_LOST_REDUCED,
+      NULL);
+    goto cleanup;
+  }
+  if (sold_reduced)
+  {
+    ret = TALER_MHD_reply_with_error (
+      connection,
+      MHD_HTTP_CONFLICT,
+      TALER_EC_MERCHANT_PRIVATE_PATCH_PRODUCTS_TOTAL_SOLD_REDUCED,
+      NULL);
+    goto cleanup;
+  }
+  if (stock_reduced)
+  {
+    ret = TALER_MHD_reply_with_error (
+      connection,
+      MHD_HTTP_CONFLICT,
+      TALER_EC_MERCHANT_PRIVATE_PATCH_PRODUCTS_TOTAL_STOCKED_REDUCED,
+      NULL);
+    goto cleanup;
   }
+  /* success! */
+  ret = TALER_MHD_reply_static (connection,
+                                MHD_HTTP_NO_CONTENT,
+                                NULL,
+                                NULL,
+                                0);
+cleanup:
+  GNUNET_free (cats);
+  GNUNET_JSON_parse_free (spec);
+  return ret;
 }
 
 
diff --git a/src/backend/taler-merchant-httpd_private-post-orders.c b/src/backend/taler-merchant-httpd_private-post-orders.c
index eedece55..8bdae3f1 100644
--- a/src/backend/taler-merchant-httpd_private-post-orders.c
+++ b/src/backend/taler-merchant-httpd_private-post-orders.c
@@ -940,6 +940,8 @@ execute_order (struct OrderContext *oc)
     struct TALER_MERCHANTDB_ProductDetails pd;
     MHD_RESULT ret;
     const struct InventoryProduct *ip;
+    size_t num_categories = 0;
+    uint64_t *categories = NULL;
 
     ip = &oc->parse_request.inventory_products[
       oc->execute_order.out_of_stock_index];
@@ -950,10 +952,13 @@ execute_order (struct OrderContext *oc)
       TMH_db->cls,
       oc->hc->instance->settings.id,
       ip->product_id,
-      &pd);
+      &pd,
+      &num_categories,
+      &categories);
     switch (qs)
     {
     case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
+      GNUNET_free (categories);
       GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                   "Order creation failed: product out of stock\n");
       ret = TALER_MHD_REPLY_JSON_PACK (
@@ -1317,6 +1322,7 @@ get_exchange_keys (void *cls,
                                         rx);
 }
 
+
 /**
  * Fetch details about the token family with the given @a slug
  * and add them to the list of token authorities. Check if the
@@ -1340,12 +1346,13 @@ set_token_authority (struct OrderContext *oc,
     // TODO: make this configurable. This is the granularity of token
     //       expiration dates.
     GNUNET_TIME_UNIT_DAYS
-  );
+    );
 
   qs = TMH_db->lookup_token_family_key (TMH_db->cls,
                                         oc->hc->instance->settings.id,
                                         slug,
-                                        GNUNET_TIME_absolute_to_timestamp (min_start_date),
+                                        GNUNET_TIME_absolute_to_timestamp (
+                                          min_start_date),
                                         start_date,
                                         &key_details);
 
@@ -1390,9 +1397,10 @@ set_token_authority (struct OrderContext *oc,
     struct GNUNET_CRYPTO_BlindSignPrivateKey *priv;
     struct GNUNET_CRYPTO_BlindSignPublicKey *pub;
     struct GNUNET_TIME_Absolute now = GNUNET_TIME_absolute_get ();
-    struct GNUNET_TIME_Timestamp valid_before = GNUNET_TIME_absolute_to_timestamp(
-      GNUNET_TIME_absolute_add (now,
-                                key_details.token_family.duration));
+    struct GNUNET_TIME_Timestamp valid_before =
+      GNUNET_TIME_absolute_to_timestamp (
+        GNUNET_TIME_absolute_add (now,
+                                  key_details.token_family.duration));
 
     GNUNET_CRYPTO_blind_sign_keys_create (&priv,
                                           &pub,
@@ -1411,13 +1419,16 @@ set_token_authority (struct OrderContext *oc,
                                           slug,
                                           &token_pub,
                                           &token_priv,
-                                          GNUNET_TIME_absolute_to_timestamp (now),
+                                          GNUNET_TIME_absolute_to_timestamp (now
+                                                                             ),
                                           valid_before);
 
     authority.token_expiration = valid_before;
     authority.pub = &token_pub;
     // GNUNET_CRYPTO_blind_sign_priv_decref (&token_priv.private_key);
-  } else {
+  }
+  else
+  {
     authority.token_expiration = key_details.valid_before;
     authority.pub = key_details.pub;
   }
@@ -1428,11 +1439,13 @@ set_token_authority (struct OrderContext *oc,
 
   GNUNET_free (key_details.token_family.slug);
   GNUNET_free (key_details.token_family.name);
-  if (NULL != key_details.priv) {
+  if (NULL != key_details.priv)
+  {
     GNUNET_CRYPTO_blind_sign_priv_decref (&key_details.priv->private_key);
   }
 
-  switch (key_details.token_family.kind) {
+  switch (key_details.token_family.kind)
+  {
   case TALER_MERCHANTDB_TFK_Subscription:
     authority.kind = TALER_MCTK_SUBSCRIPTION;
     authority.details.subscription.start_date = key_details.valid_after;
@@ -1454,6 +1467,7 @@ set_token_authority (struct OrderContext *oc,
   return MHD_YES;
 }
 
+
 /**
  * Serialize order into @a oc->serialize_order.contract,
  * ready to be stored in the database. Upon success, continue
@@ -1472,16 +1486,16 @@ serialize_order (struct OrderContext *oc)
 
   merchant = GNUNET_JSON_PACK (
     GNUNET_JSON_pack_string ("name",
-                              settings->name),
+                             settings->name),
     GNUNET_JSON_pack_allow_null (
       GNUNET_JSON_pack_string ("website",
-                                settings->website)),
+                               settings->website)),
     GNUNET_JSON_pack_allow_null (
       GNUNET_JSON_pack_string ("email",
-                                settings->email)),
+                               settings->email)),
     GNUNET_JSON_pack_allow_null (
       GNUNET_JSON_pack_string ("logo",
-                                settings->logo)));
+                               settings->logo)));
   GNUNET_assert (NULL != merchant);
   {
     json_t *loca;
@@ -1493,7 +1507,7 @@ serialize_order (struct OrderContext *oc)
       loca = json_deep_copy (loca);
       GNUNET_assert (NULL != loca);
       GNUNET_assert (0 ==
-                      json_object_set_new (merchant,
+                     json_object_set_new (merchant,
                                           "address",
                                           loca));
     }
@@ -1508,7 +1522,7 @@ serialize_order (struct OrderContext *oc)
       juri = json_deep_copy (juri);
       GNUNET_assert (NULL != juri);
       GNUNET_assert (0 ==
-                      json_object_set_new (merchant,
+                     json_object_set_new (merchant,
                                           "jurisdiction",
                                           juri));
     }
@@ -1516,7 +1530,8 @@ serialize_order (struct OrderContext *oc)
 
   for (unsigned int i = 0; i<oc->parse_choices.authorities_len; i++)
   {
-    struct TALER_MerchantContractTokenAuthority *authority = &oc->parse_choices.authorities[i];
+    struct TALER_MerchantContractTokenAuthority *authority = &oc->parse_choices.
+                                                             authorities[i];
 
     // TODO: Finish spec to clearly define how token families are stored in
     //       ContractTerms.
@@ -1529,7 +1544,7 @@ serialize_order (struct OrderContext *oc)
     //         so it's clear with key is referenced.
     json_t *jauthority = GNUNET_JSON_PACK (
       GNUNET_JSON_pack_string ("description",
-                                authority->description),
+                               authority->description),
       GNUNET_JSON_pack_allow_null (
         GNUNET_JSON_pack_object_incref ("description_i18n",
                                         authority->description_i18n)),
@@ -1539,10 +1554,10 @@ serialize_order (struct OrderContext *oc)
                                   &authority->pub->public_key.pub_key_hash),
       GNUNET_JSON_pack_timestamp ("token_expiration",
                                   authority->token_expiration)
-    );
+      );
 
     GNUNET_assert (0 ==
-                    json_object_set_new (token_types,
+                   json_object_set_new (token_types,
                                         authority->label,
                                         jauthority));
   }
@@ -1561,20 +1576,21 @@ serialize_order (struct OrderContext *oc)
       json_t *jinput = GNUNET_JSON_PACK (
         GNUNET_JSON_pack_int64 ("type",
                                 input->type)
-      );
+        );
 
       if (TALER_MCIT_TOKEN == input->type)
       {
-        GNUNET_assert(0 ==
-                      json_object_set_new(jinput,
-                                          "number",
-                                          json_integer (
-                                            input->details.token.count)));
-        GNUNET_assert(0 ==
-                      json_object_set_new(jinput,
-                                          "token_family_slug",
-                                          json_string (
-                                            input->details.token.token_family_slug)));
+        GNUNET_assert (0 ==
+                       json_object_set_new (jinput,
+                                            "number",
+                                            json_integer (
+                                              input->details.token.count)));
+        GNUNET_assert (0 ==
+                       json_object_set_new (jinput,
+                                            "token_family_slug",
+                                            json_string (
+                                              input->details.token.
+                                              token_family_slug)));
       }
 
       GNUNET_assert (0 == json_array_append_new (inputs, jinput));
@@ -1587,21 +1603,22 @@ serialize_order (struct OrderContext *oc)
       json_t *joutput = GNUNET_JSON_PACK (
         GNUNET_JSON_pack_int64 ("type",
                                 output->type)
-      );
+        );
 
       if (TALER_MCOT_TOKEN == output->type)
       {
-        GNUNET_assert(0 ==
-                      json_object_set_new(joutput,
-                                          "number",
-                                          json_integer (
-                                            output->details.token.count)));
-
-        GNUNET_assert(0 ==
-                      json_object_set_new(joutput,
-                                          "token_family_slug",
-                                          json_string (
-                                            output->details.token.token_family_slug)));
+        GNUNET_assert (0 ==
+                       json_object_set_new (joutput,
+                                            "number",
+                                            json_integer (
+                                              output->details.token.count)));
+
+        GNUNET_assert (0 ==
+                       json_object_set_new (joutput,
+                                            "token_family_slug",
+                                            json_string (
+                                              output->details.token.
+                                              token_family_slug)));
       }
 
       GNUNET_assert (0 == json_array_append (outputs, joutput));
@@ -1609,10 +1626,10 @@ serialize_order (struct OrderContext *oc)
 
     json_t *jchoice = GNUNET_JSON_PACK (
       GNUNET_JSON_pack_array_incref ("inputs",
-                                      inputs),
+                                     inputs),
       GNUNET_JSON_pack_array_incref ("outputs",
-                                      outputs)
-    );
+                                     outputs)
+      );
 
     GNUNET_assert (0 == json_array_append (choices, jchoice));
   }
@@ -1633,7 +1650,8 @@ serialize_order (struct OrderContext *oc)
                                oc->parse_order.fulfillment_message)),
     GNUNET_JSON_pack_allow_null (
       GNUNET_JSON_pack_object_incref ("fulfillment_message_i18n",
-                                      oc->parse_order.fulfillment_message_i18n)),
+                                      oc->parse_order.fulfillment_message_i18n))
+    ,
     GNUNET_JSON_pack_allow_null (
       GNUNET_JSON_pack_string ("fulfillment_url",
                                oc->parse_order.fulfillment_url)),
@@ -1674,12 +1692,12 @@ serialize_order (struct OrderContext *oc)
                             &oc->parse_order.brutto),
     GNUNET_JSON_pack_allow_null (
       GNUNET_JSON_pack_array_incref ("choices",
-                                      choices)
-    ),
+                                     choices)
+      ),
     GNUNET_JSON_pack_allow_null (
       GNUNET_JSON_pack_object_incref ("token_types",
                                       token_types)
-    ),
+      ),
     GNUNET_JSON_pack_allow_null (
       GNUNET_JSON_pack_object_incref ("extra",
                                       (json_t *) oc->parse_order.extra))
@@ -1715,6 +1733,7 @@ serialize_order (struct OrderContext *oc)
   oc->phase++;
 }
 
+
 /**
  * Set max_fee in @a oc based on STEFAN value if
  * not yet present. Upon success, continue
@@ -1750,6 +1769,7 @@ set_max_fee (struct OrderContext *oc)
   oc->phase++;
 }
 
+
 /**
  * Set list of acceptable exchanges in @a oc. Upon success, continue
  * processing with set_max_fee().
@@ -1871,7 +1891,7 @@ parse_order (struct OrderContext *oc)
       NULL),
     GNUNET_JSON_spec_mark_optional (
       GNUNET_JSON_spec_array_const ("choices",
-                                   &oc->parse_order.choices),
+                                    &oc->parse_order.choices),
       NULL),
     GNUNET_JSON_spec_mark_optional (
       TALER_JSON_spec_web_url ("merchant_base_url",
@@ -1937,7 +1957,7 @@ parse_order (struct OrderContext *oc)
                      ret);
     return;
   }
-  if (NULL == version || 0 == strcmp("0", version))
+  if (NULL == version || 0 == strcmp ("0", version))
   {
     oc->parse_order.version = TALER_MCV_V0;
 
@@ -1952,11 +1972,11 @@ parse_order (struct OrderContext *oc)
       return;
     }
   }
-  else if (0 == strcmp("1", version))
+  else if (0 == strcmp ("1", version))
   {
     oc->parse_order.version = TALER_MCV_V1;
 
-    if (! json_is_array(oc->parse_order.choices))
+    if (! json_is_array (oc->parse_order.choices))
     {
       GNUNET_break_op (0);
       GNUNET_JSON_parse_free (spec);
@@ -1989,9 +2009,9 @@ parse_order (struct OrderContext *oc)
     return;
   }
   if ( (! no_fee) &&
-      (GNUNET_OK !=
-       TALER_amount_cmp_currency (&oc->parse_order.brutto,
-                                  &oc->parse_order.max_fee)) )
+       (GNUNET_OK !=
+        TALER_amount_cmp_currency (&oc->parse_order.brutto,
+                                   &oc->parse_order.max_fee)) )
   {
     GNUNET_break_op (0);
     GNUNET_JSON_parse_free (spec);
@@ -2268,6 +2288,7 @@ parse_order (struct OrderContext *oc)
   oc->phase++;
 }
 
+
 /**
  * Parse contract choices. Upon success, continue
  * processing with merge_inventory().
@@ -2355,7 +2376,7 @@ parse_choices (struct OrderContext *oc)
             GNUNET_JSON_spec_uint32 ("count",
                                      &input.details.token.count),
             NULL),
-          GNUNET_JSON_spec_end()
+          GNUNET_JSON_spec_end ()
         };
 
         if (GNUNET_OK !=
@@ -2431,7 +2452,8 @@ parse_choices (struct OrderContext *oc)
       size_t idx;
       json_array_foreach ((json_t *) joutputs, idx, joutput)
       {
-        struct TALER_MerchantContractOutput output = { .details.token.count = 1 };
+        struct TALER_MerchantContractOutput output = { .details.token.count = 1}
+        ;
         const char *kind;
         const char *ierror_name;
         unsigned int ierror_line;
@@ -2447,14 +2469,14 @@ parse_choices (struct OrderContext *oc)
             GNUNET_JSON_spec_uint32 ("count",
                                      &output.details.token.count),
             NULL),
-          GNUNET_JSON_spec_end()
+          GNUNET_JSON_spec_end ()
         };
 
         if (GNUNET_OK !=
             GNUNET_JSON_parse (joutput,
-                              ispec,
-                              &ierror_name,
-                              &ierror_line))
+                               ispec,
+                               &ierror_name,
+                               &ierror_line))
         {
           GNUNET_JSON_parse_free (spec);
           GNUNET_JSON_parse_free (ispec);
@@ -2526,6 +2548,7 @@ parse_choices (struct OrderContext *oc)
   oc->phase++;
 }
 
+
 /**
  * Process the @a payment_target and add the details of how the
  * order could be paid to @a order. On success, continue
@@ -2591,11 +2614,15 @@ merge_inventory (struct OrderContext *oc)
         = &oc->parse_request.inventory_products[i];
       struct TALER_MERCHANTDB_ProductDetails pd;
       enum GNUNET_DB_QueryStatus qs;
+      size_t num_categories = 0;
+      uint64_t *categories = NULL;
 
       qs = TMH_db->lookup_product (TMH_db->cls,
                                    oc->hc->instance->settings.id,
                                    ip->product_id,
-                                   &pd);
+                                   &pd,
+                                   &num_categories,
+                                   &categories);
       if (qs <= 0)
       {
         enum TALER_ErrorCode ec = TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE;
@@ -2631,6 +2658,7 @@ merge_inventory (struct OrderContext *oc)
                           ip->product_id);
         return;
       }
+      GNUNET_free (categories);
       oc->parse_order.minimum_age
         = GNUNET_MAX (oc->parse_order.minimum_age,
                       pd.minimum_age);
diff --git a/src/backend/taler-merchant-httpd_private-post-products-ID-lock.c b/src/backend/taler-merchant-httpd_private-post-products-ID-lock.c
index 184f1d28..844b2ec8 100644
--- a/src/backend/taler-merchant-httpd_private-post-products-ID-lock.c
+++ b/src/backend/taler-merchant-httpd_private-post-products-ID-lock.c
@@ -29,9 +29,10 @@
 
 
 MHD_RESULT
-TMH_private_post_products_ID_lock (const struct TMH_RequestHandler *rh,
-                                   struct MHD_Connection *connection,
-                                   struct TMH_HandlerContext *hc)
+TMH_private_post_products_ID_lock (
+  const struct TMH_RequestHandler *rh,
+  struct MHD_Connection *connection,
+  struct TMH_HandlerContext *hc)
 {
   struct TMH_MerchantInstance *mi = hc->instance;
   const char *product_id = hc->infix;
@@ -75,35 +76,48 @@ TMH_private_post_products_ID_lock (const struct TMH_RequestHandler *rh,
   switch (qs)
   {
   case GNUNET_DB_STATUS_HARD_ERROR:
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_INTERNAL_SERVER_ERROR,
-                                       TALER_EC_GENERIC_DB_STORE_FAILED,
-                                       NULL);
+    return TALER_MHD_reply_with_error (
+      connection,
+      MHD_HTTP_INTERNAL_SERVER_ERROR,
+      TALER_EC_GENERIC_DB_STORE_FAILED,
+      NULL);
   case GNUNET_DB_STATUS_SOFT_ERROR:
     GNUNET_break (0);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_INTERNAL_SERVER_ERROR,
-                                       TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE,
-                                       "Serialization error for single-statment request");
+    return TALER_MHD_reply_with_error (
+      connection,
+      MHD_HTTP_INTERNAL_SERVER_ERROR,
+      TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE,
+      "Serialization error for single-statment request");
   case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
-    qs = TMH_db->lookup_product (TMH_db->cls,
-                                 mi->settings.id,
-                                 product_id,
-                                 NULL);
-    if (GNUNET_DB_STATUS_HARD_ERROR == qs)
-      return TALER_MHD_reply_with_error (connection,
-                                         MHD_HTTP_INTERNAL_SERVER_ERROR,
-                                         TALER_EC_GENERIC_DB_STORE_FAILED,
-                                         "lookup_product");
-    if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
-      return TALER_MHD_reply_with_error (connection,
-                                         MHD_HTTP_NOT_FOUND,
-                                         TALER_EC_MERCHANT_GENERIC_PRODUCT_UNKNOWN,
-                                         product_id);
-    return TALER_MHD_reply_with_error (connection,
-                                       MHD_HTTP_GONE,
-                                       TALER_EC_MERCHANT_PRIVATE_POST_PRODUCTS_LOCK_INSUFFICIENT_STOCKS,
-                                       product_id);
+    {
+      size_t num_categories = 0;
+      uint64_t *categories = NULL;
+
+      qs = TMH_db->lookup_product (TMH_db->cls,
+                                   mi->settings.id,
+                                   product_id,
+                                   NULL,
+                                   &num_categories,
+                                   &categories);
+      if (GNUNET_DB_STATUS_HARD_ERROR == qs)
+        return TALER_MHD_reply_with_error (
+          connection,
+          MHD_HTTP_INTERNAL_SERVER_ERROR,
+          TALER_EC_GENERIC_DB_STORE_FAILED,
+          "lookup_product");
+      if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
+        return TALER_MHD_reply_with_error (
+          connection,
+          MHD_HTTP_NOT_FOUND,
+          TALER_EC_MERCHANT_GENERIC_PRODUCT_UNKNOWN,
+          product_id);
+      GNUNET_free (categories);
+    }
+    return TALER_MHD_reply_with_error (
+      connection,
+      MHD_HTTP_GONE,
+      TALER_EC_MERCHANT_PRIVATE_POST_PRODUCTS_LOCK_INSUFFICIENT_STOCKS,
+      product_id);
   case GNUNET_DB_STATUS_SUCCESS_ONE_RESULT:
     return TALER_MHD_reply_static (connection,
                                    MHD_HTTP_NO_CONTENT,
diff --git a/src/backenddb/Makefile.am b/src/backenddb/Makefile.am
index 99ef1e77..4cacd3b4 100644
--- a/src/backenddb/Makefile.am
+++ b/src/backenddb/Makefile.am
@@ -63,7 +63,7 @@ libtalermerchantdb_la_LIBADD = \
 
 libtalermerchantdb_la_LDFLAGS = \
   $(POSTGRESQL_LDFLAGS) \
-  -version-info 3:1:1 \
+  -version-info 4:0:2 \
   -no-undefined
 
 libtaler_plugin_merchantdb_postgres_la_SOURCES = \
diff --git a/src/backenddb/pg_insert_product.c b/src/backenddb/pg_insert_product.c
index c46255c9..0d0a8380 100644
--- a/src/backenddb/pg_insert_product.c
+++ b/src/backenddb/pg_insert_product.c
@@ -72,7 +72,6 @@ TMH_PG_insert_product (void *cls,
   };
   enum GNUNET_DB_QueryStatus qs;
 
-  *no_cat = -1;
   check_connection (pg);
   PREPARE (pg,
            "insert_product",
diff --git a/src/backenddb/pg_lookup_all_products.c b/src/backenddb/pg_lookup_all_products.c
index 29751a45..31320d59 100644
--- a/src/backenddb/pg_lookup_all_products.c
+++ b/src/backenddb/pg_lookup_all_products.c
@@ -41,6 +41,11 @@ struct LookupProductsContext
   void *cb_cls;
 
   /**
+   * Postgres context.
+   */
+  struct PostgresClosure *pg;
+
+  /**
    * Did database result extraction fail?
    */
   bool extract_failed;
@@ -61,12 +66,15 @@ lookup_products_cb (void *cls,
                     unsigned int num_results)
 {
   struct LookupProductsContext *plc = cls;
+  struct PostgresClosure *pg = plc->pg;
 
   for (unsigned int i = 0; i < num_results; i++)
   {
     char *product_id;
     uint64_t product_serial;
     struct TALER_MERCHANTDB_ProductDetails pd;
+    size_t num_categories;
+    uint64_t *categories;
     struct GNUNET_PQ_ResultSpec rs[] = {
       GNUNET_PQ_result_spec_string ("product_id",
                                     &product_id),
@@ -79,7 +87,7 @@ lookup_products_cb (void *cls,
       GNUNET_PQ_result_spec_string ("unit",
                                     &pd.unit),
       TALER_PQ_result_spec_amount_with_currency ("price",
-                                   &pd.price),
+                                                 &pd.price),
       TALER_PQ_result_spec_json ("taxes",
                                  &pd.taxes),
       GNUNET_PQ_result_spec_uint64 ("total_stock",
@@ -96,6 +104,10 @@ lookup_products_cb (void *cls,
                                        &pd.next_restock),
       GNUNET_PQ_result_spec_uint32 ("minimum_age",
                                     &pd.minimum_age),
+      GNUNET_PQ_result_spec_array_uint64 (pg->conn,
+                                          "categories",
+                                          &num_categories,
+                                          &categories),
       GNUNET_PQ_result_spec_end
     };
 
@@ -111,7 +123,9 @@ lookup_products_cb (void *cls,
     plc->cb (plc->cb_cls,
              product_serial,
              product_id,
-             &pd);
+             &pd,
+             num_categories,
+             categories);
     GNUNET_PQ_cleanup_result (rs);
   }
 }
@@ -119,14 +133,15 @@ lookup_products_cb (void *cls,
 
 enum GNUNET_DB_QueryStatus
 TMH_PG_lookup_all_products (void *cls,
-                        const char *instance_id,
-                        TALER_MERCHANTDB_ProductCallback cb,
-                        void *cb_cls)
+                            const char *instance_id,
+                            TALER_MERCHANTDB_ProductCallback cb,
+                            void *cb_cls)
 {
   struct PostgresClosure *pg = cls;
   struct LookupProductsContext plc = {
     .cb = cb,
     .cb_cls = cb_cls,
+    .pg = pg,
     /* Can be overwritten by the lookup_products_cb */
     .extract_failed = false,
   };
@@ -157,6 +172,13 @@ TMH_PG_lookup_all_products (void *cls,
            " FROM merchant_inventory"
            " JOIN merchant_instances"
            "   USING (merchant_serial)"
+           ",LATERAL ("
+           "   SELECT ARRAY ("
+           "     SELECT mpc.category_serial"
+           "       FROM merchant_product_categories mpc"
+           "      WHERE mpc.product_serial = mi.product_serial"
+           "   ) AS category_array"
+           " ) t"
            " WHERE merchant_instances.merchant_id=$1");
   qs = GNUNET_PQ_eval_prepared_multi_select (
     pg->conn,
diff --git a/src/backenddb/pg_lookup_product.c b/src/backenddb/pg_lookup_product.c
index a078cf8e..2948e6ca 100644
--- a/src/backenddb/pg_lookup_product.c
+++ b/src/backenddb/pg_lookup_product.c
@@ -29,7 +29,9 @@ enum GNUNET_DB_QueryStatus
 TMH_PG_lookup_product (void *cls,
                        const char *instance_id,
                        const char *product_id,
-                       struct TALER_MERCHANTDB_ProductDetails *pd)
+                       struct TALER_MERCHANTDB_ProductDetails *pd,
+                       size_t *num_categories,
+                       uint64_t **categories)
 {
   struct PostgresClosure *pg = cls;
   struct GNUNET_PQ_QueryParam params[] = {
@@ -38,6 +40,35 @@ TMH_PG_lookup_product (void *cls,
     GNUNET_PQ_query_param_end
   };
 
+  PREPARE (pg,
+           "lookup_product",
+           "SELECT"
+           " mi.description"
+           ",mi.description_i18n"
+           ",mi.unit"
+           ",mi.price"
+           ",mi.taxes"
+           ",mi.total_stock"
+           ",mi.total_sold"
+           ",mi.total_lost"
+           ",mi.image"
+           ",mi.address"
+           ",mi.next_restock"
+           ",mi.minimum_age"
+           ",t.category_array AS categories"
+           " FROM merchant_inventory mi"
+           " JOIN merchant_instances inst"
+           "   USING (merchant_serial)"
+           ",LATERAL ("
+           "   SELECT ARRAY ("
+           "     SELECT mpc.category_serial"
+           "       FROM merchant_product_categories mpc"
+           "      WHERE mpc.product_serial = mi.product_serial"
+           "   ) AS category_array"
+           " ) t"
+           " WHERE inst.merchant_id=$1"
+           "   AND mi.product_id=$2"
+           );
   if (NULL == pd)
   {
     struct GNUNET_PQ_ResultSpec rs_null[] = {
@@ -77,30 +108,14 @@ TMH_PG_lookup_product (void *cls,
                                        &pd->next_restock),
       GNUNET_PQ_result_spec_uint32 ("minimum_age",
                                     &pd->minimum_age),
+      GNUNET_PQ_result_spec_array_uint64 (pg->conn,
+                                          "categories",
+                                          num_categories,
+                                          categories),
       GNUNET_PQ_result_spec_end
     };
 
     check_connection (pg);
-    PREPARE (pg,
-             "lookup_product",
-             "SELECT"
-             " description"
-             ",description_i18n"
-             ",unit"
-             ",price"
-             ",taxes"
-             ",total_stock"
-             ",total_sold"
-             ",total_lost"
-             ",image"
-             ",merchant_inventory.address"
-             ",next_restock"
-             ",minimum_age"
-             " FROM merchant_inventory"
-             " JOIN merchant_instances"
-             "   USING (merchant_serial)"
-             " WHERE merchant_instances.merchant_id=$1"
-             "   AND merchant_inventory.product_id=$2");
     return GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                      "lookup_product",
                                                      params,
diff --git a/src/backenddb/pg_lookup_product.h b/src/backenddb/pg_lookup_product.h
index a6add4cb..7346cc0d 100644
--- a/src/backenddb/pg_lookup_product.h
+++ b/src/backenddb/pg_lookup_product.h
@@ -33,12 +33,17 @@
  * @param product_id product to lookup
  * @param[out] pd set to the product details on success, can be NULL
  *             (in that case we only want to check if the product exists)
+ * @param[out] num_categories set to length of @a categories array
+ * @param[out] categories set to array of categories the
+ *   product is in, caller must free() it.
  * @return database result code
  */
 enum GNUNET_DB_QueryStatus
 TMH_PG_lookup_product (void *cls,
                        const char *instance_id,
                        const char *product_id,
-                       struct TALER_MERCHANTDB_ProductDetails *pd);
+                       struct TALER_MERCHANTDB_ProductDetails *pd,
+                       size_t *num_categories,
+                       uint64_t **categories);
 
 #endif
diff --git a/src/backenddb/pg_update_product.c b/src/backenddb/pg_update_product.c
index cd7c1857..d7b63b82 100644
--- a/src/backenddb/pg_update_product.c
+++ b/src/backenddb/pg_update_product.c
@@ -1,6 +1,6 @@
 /*
    This file is part of TALER
-   Copyright (C) 2022 Taler Systems SA
+   Copyright (C) 2022, 2024 Taler Systems SA
 
    TALER is free software; you can redistribute it and/or modify it under the
    terms of the GNU General Public License as published by the Free Software
@@ -26,11 +26,20 @@
 #include "pg_update_product.h"
 #include "pg_helper.h"
 
+
 enum GNUNET_DB_QueryStatus
 TMH_PG_update_product (void *cls,
                        const char *instance_id,
                        const char *product_id,
-                       const struct TALER_MERCHANTDB_ProductDetails *pd)
+                       const struct TALER_MERCHANTDB_ProductDetails *pd,
+                       size_t num_cats,
+                       const uint64_t *cats,
+                       bool *no_instance,
+                       ssize_t *no_cat,
+                       bool *no_product,
+                       bool *lost_reduced,
+                       bool *sold_reduced,
+                       bool *stocked_reduced)
 {
   struct PostgresClosure *pg = cls;
   struct GNUNET_PQ_QueryParam params[] = {
@@ -42,14 +51,37 @@ TMH_PG_update_product (void *cls,
     GNUNET_PQ_query_param_string (pd->image), /* $6 */
     TALER_PQ_query_param_json (pd->taxes),
     TALER_PQ_query_param_amount_with_currency (pg->conn,
-                                 &pd->price),       /* $8 */
+                                               &pd->price), /* $8 */
     GNUNET_PQ_query_param_uint64 (&pd->total_stock),  /* $9 */
     GNUNET_PQ_query_param_uint64 (&pd->total_lost),
     TALER_PQ_query_param_json (pd->address),
     GNUNET_PQ_query_param_timestamp (&pd->next_restock),
     GNUNET_PQ_query_param_uint32 (&pd->minimum_age),
+    GNUNET_PQ_query_param_array_uint64 (num_cats,
+                                        cats,
+                                        pg->conn),
     GNUNET_PQ_query_param_end
   };
+  uint64_t ncat;
+  bool cats_found = true;
+  struct GNUNET_PQ_ResultSpec rs[] = {
+    GNUNET_PQ_result_spec_bool ("no_instance",
+                                no_instance),
+    GNUNET_PQ_result_spec_bool ("no_product",
+                                no_product),
+    GNUNET_PQ_result_spec_bool ("lost_reduced",
+                                lost_reduced),
+    GNUNET_PQ_result_spec_bool ("sold_reduced",
+                                sold_reduced),
+    GNUNET_PQ_result_spec_bool ("stocked_reduced",
+                                stocked_reduced),
+    GNUNET_PQ_result_spec_allow_null (
+      GNUNET_PQ_result_spec_uint64 ("no_cat",
+                                    &ncat),
+      &cats_found),
+    GNUNET_PQ_result_spec_end
+  };
+  enum GNUNET_DB_QueryStatus qs;
 
   if ( (pd->total_stock < pd->total_lost + pd->total_sold) ||
        (pd->total_lost < pd->total_lost
@@ -61,26 +93,20 @@ TMH_PG_update_product (void *cls,
   check_connection (pg);
   PREPARE (pg,
            "update_product",
-           "UPDATE merchant_inventory SET"
-           " description=$3"
-           ",description_i18n=$4"
-           ",unit=$5"
-           ",image=$6"
-           ",taxes=$7"
-           ",price=$8"
-           ",total_stock=$9"
-           ",total_lost=$10"
-           ",address=$11"
-           ",next_restock=$12"
-           ",minimum_age=$13"
-           " WHERE merchant_serial="
-           "   (SELECT merchant_serial"
-           "      FROM merchant_instances"
-           "      WHERE merchant_id=$1)"
-           "   AND product_id=$2"
-           "   AND total_stock <= $9"
-           "   AND total_lost <= $10");
-  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
-                                             "update_product",
-                                             params);
+           "SELECT"
+           " out_lost_reduced AS lost_reduced"
+           ",out_sold_reduced AS sold_reduced"
+           ",out_stocked_reduced AS stocked_reduced"
+           ",out_no_product AS no_product"
+           ",out_no_cat AS no_cat"
+           ",out_no_instance AS no_instance"
+           " FROM merchant_do_update_product"
+           "($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14);");
+  qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
+                                                 "update_product",
+                                                 params,
+                                                 rs);
+  GNUNET_PQ_cleanup_query_params_closures (params);
+  *no_cat = (cats_found) ? -1 : (ssize_t) ncat;
+  return qs;
 }
diff --git a/src/backenddb/pg_update_product.h b/src/backenddb/pg_update_product.h
index 3ad280ef..ffba1073 100644
--- a/src/backenddb/pg_update_product.h
+++ b/src/backenddb/pg_update_product.h
@@ -28,26 +28,40 @@
 /**
  * Update details about a particular product. Note that the
  * transaction must enforce that the sold/stocked/lost counters
- * are not reduced (i.e. by expanding the WHERE clause on the existing
- * values).
+ * are not reduced.
  *
  * @param cls closure
  * @param instance_id instance to lookup products for
  * @param product_id product to lookup
+ * @param num_cats length of @a cats array
+ * @param cats number of categories the product is in
+ * @param[out] no_instance the update failed as the instance is unknown
+ * @param[out] no_cat set to -1 on success, otherwise the update failed and this is set
+ *                to the index of a category in @a cats that is unknown
+ * @param[out] no_product the @a product_id is unknown
+ * @param[out] lost_reduced the update failed as the counter of units lost would have been lowered
+ * @param[out] sold_reduced the update failed as the counter of units sold would have been lowered
+ * @param[out] stocked_reduced the update failed as the counter of units stocked would have been lowered
  * @param[out] pd set to the product details on success, can be NULL
  *             (in that case we only want to check if the product exists)
  *             total_sold in @a pd is ignored, total_lost must not
  *             exceed total_stock minus the existing total_sold;
  *             total_sold and total_stock must be larger or equal to
  *             the existing value;
- * @return database result code, #GNUNET_DB_STATUS_SUCCESS_NO_RESULTS if the
- *         non-decreasing constraints are not met *or* if the product
- *         does not yet exist.
+ * @return database result code
  */
 enum GNUNET_DB_QueryStatus
 TMH_PG_update_product (void *cls,
                        const char *instance_id,
                        const char *product_id,
-                       const struct TALER_MERCHANTDB_ProductDetails *pd);
+                       const struct TALER_MERCHANTDB_ProductDetails *pd,
+                       size_t num_cats,
+                       const uint64_t *cats,
+                       bool *no_instance,
+                       ssize_t *no_cat,
+                       bool *no_product,
+                       bool *lost_reduced,
+                       bool *sold_reduced,
+                       bool *stocked_reduced);
 
 #endif
diff --git a/src/backenddb/pg_update_product.sql b/src/backenddb/pg_update_product.sql
new file mode 100644
index 00000000..6b5a416b
--- /dev/null
+++ b/src/backenddb/pg_update_product.sql
@@ -0,0 +1,139 @@
+--
+-- This file is part of TALER
+-- Copyright (C) 2024 Taler Systems SA
+--
+-- TALER is free software; you can redistribute it and/or modify it under the
+-- terms of the GNU General Public License as published by the Free Software
+-- Foundation; either version 3, or (at your option) any later version.
+--
+-- TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+-- WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+-- A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License along with
+-- TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+--
+
+
+CREATE OR REPLACE FUNCTION merchant_do_update_product (
+  IN in_instance_id TEXT,
+  IN in_product_id TEXT,
+  IN in_description TEXT,
+  IN in_description_i18n BYTEA,
+  IN in_unit TEXT,
+  IN in_image TEXT,
+  IN in_taxes BYTEA,
+  IN in_price taler_amount_currency,
+  IN in_total_stock INT8,
+  IN in_total_lost INT8,
+  IN in_address BYTEA,
+  IN in_next_restock INT8,
+  IN in_minimum_age INT4,
+  IN ina_categories INT8[],
+  OUT out_no_instance BOOL,
+  OUT out_no_product BOOL,
+  OUT out_lost_reduced BOOL,
+  OUT out_sold_reduced BOOL,
+  OUT out_stocked_reduced BOOL,
+  OUT out_no_cat INT8)
+LANGUAGE plpgsql
+AS $$
+DECLARE
+  my_merchant_id INT8;
+  my_product_serial INT8;
+  i INT8;
+  ini_cat INT8;
+  rec RECORD;
+BEGIN
+
+out_no_instance=FALSE;
+out_no_product=FALSE;
+out_lost_reduced=FALSE;
+out_sold_reduced=FALSE; -- We currently don't allow updating 'sold', hence always FALSE
+out_stocked_reduced=FALSE;
+out_no_cat=NULL;
+
+-- Which instance are we using?
+SELECT merchant_serial
+  INTO my_merchant_id
+  FROM merchant_instances
+ WHERE merchant_id=in_instance_id;
+
+IF NOT FOUND
+THEN
+  out_no_instance=TRUE;
+  RETURN;
+END IF;
+
+-- Check existing entry satisfies constraints
+SELECT total_stock
+      ,total_lost
+      ,product_serial
+  INTO rec
+  FROM merchant_inventory
+ WHERE merchant_serial=my_merchant_id
+   AND product_id=in_product_id;
+
+IF NOT FOUND
+THEN
+  out_no_product=TRUE;
+  RETURN;
+END IF;
+
+my_product_serial = rec.product_serial;
+
+IF rec.total_stock > in_total_stock
+THEN
+  out_stocked_reduced=TRUE;
+  RETURN;
+END IF;
+
+IF rec.total_lost > in_total_lost
+THEN
+  out_lost_reduced=TRUE;
+  RETURN;
+END IF;
+
+-- Remove old categories
+DELETE FROM merchant_product_categories
+  WHERE product_serial=my_product_serial;
+
+-- Add new categories
+FOR i IN 1..COALESCE(array_length(ina_categories,1),0)
+LOOP
+  ini_cat=ina_categories[i];
+
+  INSERT INTO merchant_product_categories
+   (product_serial
+   ,category_serial)
+  VALUES
+   (my_product_serial
+   ,ini_cat)
+  ON CONFLICT DO NOTHING;
+
+  IF NOT FOUND
+  THEN
+    out_no_cat=i;
+    RETURN;
+  END IF;
+END LOOP;
+
+UPDATE merchant_inventory SET
+   description=in_description
+  ,description_i18n=in_description_i18n
+  ,unit=in_unit
+  ,image=in_image
+  ,taxes=in_taxes
+  ,price=in_price
+  ,total_stock=in_total_stock
+  ,total_lost=in_total_lost
+  ,address=in_address
+  ,next_restock=in_next_restock
+  ,minimum_age=in_minimum_age
+ WHERE merchant_serial=my_merchant_id
+   AND product_serial=my_product_serial; -- could also match on product_id
+
+ASSERT FOUND,'SELECTED it earlier, should UPDATE it now';
+
+-- Success!
+END $$;
diff --git a/src/backenddb/procedures.sql.in b/src/backenddb/procedures.sql.in
index 3588c2e9..9afa246b 100644
--- a/src/backenddb/procedures.sql.in
+++ b/src/backenddb/procedures.sql.in
@@ -21,5 +21,6 @@ SET search_path TO merchant;
 #include "pg_insert_deposit_to_transfer.sql"
 #include "pg_insert_product.sql"
 #include "pg_insert_transfer_details.sql"
+#include "pg_update_product.sql"
 
 COMMIT;
diff --git a/src/backenddb/test_merchantdb.c b/src/backenddb/test_merchantdb.c
index de8b2b9a..83fd8dcd 100644
--- a/src/backenddb/test_merchantdb.c
+++ b/src/backenddb/test_merchantdb.c
@@ -833,9 +833,9 @@ test_insert_product (const struct InstanceData *instance,
   if (expected_result > 0)
   {
     TEST_COND_RET_ON_FAIL (no_instance == expect_no_instance,
-                           "Conflict returned");
+                           "No instance wrong");
     TEST_COND_RET_ON_FAIL (conflict == expect_conflict,
-                           "Conflict returned");
+                           "Conflict wrong");
     TEST_COND_RET_ON_FAIL (no_cat == expected_no_cat,
                            "Wrong category missing returned");
   }
@@ -854,14 +854,54 @@ test_insert_product (const struct InstanceData *instance,
 static int
 test_update_product (const struct InstanceData *instance,
                      const struct ProductData *product,
-                     enum GNUNET_DB_QueryStatus expected_result)
+                     unsigned int num_cats,
+                     const uint64_t *cats,
+                     enum GNUNET_DB_QueryStatus expected_result,
+                     bool expect_no_instance,
+                     bool expect_no_product,
+                     bool expect_lost_reduced,
+                     bool expect_sold_reduced,
+                     bool expect_stocked_reduced,
+                     ssize_t expected_no_cat)
+
 {
-  TEST_COND_RET_ON_FAIL (expected_result ==
-                         plugin->update_product (plugin->cls,
-                                                 instance->instance.id,
-                                                 product->id,
-                                                 &product->product),
-                         "Update product failed\n");
+  bool no_instance;
+  ssize_t no_cat;
+  bool no_product;
+  bool lost_reduced;
+  bool sold_reduced;
+  bool stocked_reduced;
+
+  TEST_COND_RET_ON_FAIL (
+    expected_result ==
+    plugin->update_product (plugin->cls,
+                            instance->instance.id,
+                            product->id,
+                            &product->product,
+                            num_cats,
+                            cats,
+                            &no_instance,
+                            &no_cat,
+                            &no_product,
+                            &lost_reduced,
+                            &sold_reduced,
+                            &stocked_reduced),
+    "Update product failed\n");
+  if (expected_result > 0)
+  {
+    TEST_COND_RET_ON_FAIL (no_instance == expect_no_instance,
+                           "No instance wrong");
+    TEST_COND_RET_ON_FAIL (no_product == expect_no_product,
+                           "No product wrong");
+    TEST_COND_RET_ON_FAIL (lost_reduced == expect_lost_reduced,
+                           "No product wrong");
+    TEST_COND_RET_ON_FAIL (stocked_reduced == expect_stocked_reduced,
+                           "Stocked reduced wrong");
+    TEST_COND_RET_ON_FAIL (sold_reduced == expect_sold_reduced,
+                           "Sold reduced wrong");
+    TEST_COND_RET_ON_FAIL (no_cat == expected_no_cat,
+                           "Wrong category missing returned");
+  }
   return 0;
 }
 
@@ -878,25 +918,34 @@ test_lookup_product (const struct InstanceData *instance,
                      const struct ProductData *product)
 {
   struct TALER_MERCHANTDB_ProductDetails lookup_result;
+  size_t num_categories = 0;
+  uint64_t *categories = NULL;
+
   if (0 > plugin->lookup_product (plugin->cls,
                                   instance->instance.id,
                                   product->id,
-                                  &lookup_result))
+                                  &lookup_result,
+                                  &num_categories,
+                                  &categories))
   {
     GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                 "Lookup product failed\n");
     TALER_MERCHANTDB_product_details_free (&lookup_result);
     return 1;
   }
-  const struct TALER_MERCHANTDB_ProductDetails *to_cmp = &product->product;
-  if (0 != check_products_equal (&lookup_result,
-                                 to_cmp))
+  GNUNET_free (categories);
   {
-    GNUNET_break (0);
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "Lookup product failed: incorrect product returned\n");
-    TALER_MERCHANTDB_product_details_free (&lookup_result);
-    return 1;
+    const struct TALER_MERCHANTDB_ProductDetails *to_cmp = &product->product;
+
+    if (0 != check_products_equal (&lookup_result,
+                                   to_cmp))
+    {
+      GNUNET_break (0);
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                  "Lookup product failed: incorrect product returned\n");
+      TALER_MERCHANTDB_product_details_free (&lookup_result);
+      return 1;
+    }
   }
   TALER_MERCHANTDB_product_details_free (&lookup_result);
   return 0;
@@ -1148,15 +1197,23 @@ run_test_products (struct TestProducts_Closure *cls)
   TEST_RET_ON_FAIL (test_lookup_product (&cls->instance,
                                          &cls->products[0]));
   /* Make sure it fails correctly for products that don't exist */
-  if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS !=
-      plugin->lookup_product (plugin->cls,
-                              cls->instance.instance.id,
-                              "nonexistent_product",
-                              NULL))
   {
-    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
-                "Lookup product failed\n");
-    return 1;
+    size_t num_categories = 0;
+    uint64_t *categories = NULL;
+
+    if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS !=
+        plugin->lookup_product (plugin->cls,
+                                cls->instance.instance.id,
+                                "nonexistent_product",
+                                NULL,
+                                &num_categories,
+                                &categories))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                  "Lookup product failed\n");
+      return 1;
+    }
+    GNUNET_free (categories);
   }
   /* Test product update */
   cls->products[0].product.description =
@@ -1182,33 +1239,67 @@ run_test_products (struct TestProducts_Closure *cls)
                  json_array_append_new (cls->products[0].product.address,
                                         json_string ("444 Some Street")));
   cls->products[0].product.next_restock = GNUNET_TIME_timestamp_get ();
-  TEST_RET_ON_FAIL (test_update_product (&cls->instance,
-                                         &cls->products[0],
-                                         GNUNET_DB_STATUS_SUCCESS_ONE_RESULT));
+  TEST_RET_ON_FAIL (test_update_product (
+                      &cls->instance,
+                      &cls->products[0],
+                      0,
+                      NULL,
+                      GNUNET_DB_STATUS_SUCCESS_ONE_RESULT,
+                      false,
+                      false,
+                      false,
+                      false,
+                      false,
+                      -1));
 
   {
     struct ProductData stock_dec = cls->products[0];
 
     stock_dec.product.total_stock = 40;
-    TEST_RET_ON_FAIL (test_update_product (&cls->instance,
-                                           &stock_dec,
-                                           GNUNET_DB_STATUS_SUCCESS_NO_RESULTS))
-    ;
+    TEST_RET_ON_FAIL (test_update_product (
+                        &cls->instance,
+                        &stock_dec,
+                        0,
+                        NULL,
+                        GNUNET_DB_STATUS_SUCCESS_ONE_RESULT,
+                        false,
+                        false,
+                        false,
+                        false,
+                        true,
+                        -1));
   }
   {
     struct ProductData lost_dec = cls->products[0];
 
     lost_dec.product.total_lost = 1;
-    TEST_RET_ON_FAIL (test_update_product (&cls->instance,
-                                           &lost_dec,
-                                           GNUNET_DB_STATUS_SUCCESS_NO_RESULTS))
-    ;
+    TEST_RET_ON_FAIL (test_update_product (
+                        &cls->instance,
+                        &lost_dec,
+                        0,
+                        NULL,
+                        GNUNET_DB_STATUS_SUCCESS_ONE_RESULT,
+                        false,
+                        false,
+                        true,
+                        false,
+                        false,
+                        -1));
   }
   TEST_RET_ON_FAIL (test_lookup_product (&cls->instance,
                                          &cls->products[0]));
-  TEST_RET_ON_FAIL (test_update_product (&cls->instance,
-                                         &cls->products[1],
-                                         GNUNET_DB_STATUS_SUCCESS_NO_RESULTS));
+  TEST_RET_ON_FAIL (test_update_product (
+                      &cls->instance,
+                      &cls->products[1],
+                      0,
+                      NULL,
+                      GNUNET_DB_STATUS_SUCCESS_ONE_RESULT,
+                      false,
+                      true,
+                      false,
+                      false,
+                      false,
+                      -1));
   /* Test collective product lookup */
   TEST_RET_ON_FAIL (test_insert_product (&cls->instance,
                                          &cls->products[1],
diff --git a/src/include/taler_merchantdb_plugin.h b/src/include/taler_merchantdb_plugin.h
index 12c00833..faccc55a 100644
--- a/src/include/taler_merchantdb_plugin.h
+++ b/src/include/taler_merchantdb_plugin.h
@@ -341,13 +341,18 @@ struct TALER_MERCHANTDB_ProductDetails
  * @param product_serial row ID of the product
  * @param product_id ID of the product
  * @param pd full product details
+ * @param num_categories length of @a categories array
+ * @param categories array of categories the
+ *   product is in
  */
 typedef void
 (*TALER_MERCHANTDB_ProductCallback)(
   void *cls,
   uint64_t product_serial,
   const char *product_id,
-  const struct TALER_MERCHANTDB_ProductDetails *pd);
+  const struct TALER_MERCHANTDB_ProductDetails *pd,
+  size_t num_categories,
+  const uint64_t *categories);
 
 
 /**
@@ -1728,13 +1733,18 @@ struct TALER_MERCHANTDB_Plugin
    * @param product_id product to lookup
    * @param[out] pd set to the product details on success, can be NULL
    *             (in that case we only want to check if the product exists)
+   * @param[out] num_categories set to length of @a categories array
+   * @param[out] categories set to array of categories the
+   *   product is in, caller must free() it.
    * @return database result code
    */
   enum GNUNET_DB_QueryStatus
   (*lookup_product)(void *cls,
                     const char *instance_id,
                     const char *product_id,
-                    struct TALER_MERCHANTDB_ProductDetails *pd);
+                    struct TALER_MERCHANTDB_ProductDetails *pd,
+                    size_t *num_categories,
+                    uint64_t **categories);
 
   /**
    * Delete information about a product. Note that the transaction must
@@ -1786,21 +1796,31 @@ struct TALER_MERCHANTDB_Plugin
    * @param cls closure
    * @param instance_id instance to lookup products for
    * @param product_id product to lookup
-   * @param pd set to the product details on success, can be NULL
-   *             (in that case we only want to check if the product exists);
-   *             total_sold in @a pd is ignored (!), total_lost must not
-   *             exceed total_stock minus the existing total_sold;
-   *             total_sold and total_stock must be larger or equal to
-   *             the existing value;
-   * @return database result code, #GNUNET_DB_STATUS_SUCCESS_NO_RESULTS if the
-   *         non-decreasing constraints are not met *or* if the product
-   *         does not yet exist.
+   * @param pd product details with updated values
+   * @param num_cats length of @a cats array
+   * @param cats number of categories the product is in
+   * @param[out] no_instance the update failed as the instance is unknown
+   * @param[out] no_cat set to -1 on success, otherwise the update failed and this is set
+   *                to the index of a category in @a cats that is unknown
+   * @param[out] no_product the @a product_id is unknown
+   * @param[out] lost_reduced the update failed as the counter of units lost would have been lowered
+   * @param[out] sold_reduced the update failed as the counter of units sold would have been lowered
+   * @param[out] stocked_reduced the update failed as the counter of units stocked would have been lowered
+   * @return database result code
    */
   enum GNUNET_DB_QueryStatus
   (*update_product)(void *cls,
                     const char *instance_id,
                     const char *product_id,
-                    const struct TALER_MERCHANTDB_ProductDetails *pd);
+                    const struct TALER_MERCHANTDB_ProductDetails *pd,
+                    size_t num_cats,
+                    const uint64_t *cats,
+                    bool *no_instance,
+                    ssize_t *no_cat,
+                    bool *no_product,
+                    bool *lost_reduced,
+                    bool *sold_reduced,
+                    bool *stocked_reduced);
 
   /**
    * Lock stocks of a particular product. Note that the transaction must
diff --git a/src/lib/Makefile.am b/src/lib/Makefile.am
index 1e7430d4..d997b767 100644
--- a/src/lib/Makefile.am
+++ b/src/lib/Makefile.am
@@ -10,7 +10,7 @@ lib_LTLIBRARIES = \
   libtalermerchant.la
 
 libtalermerchant_la_LDFLAGS = \
-  -version-info 5:2:0 \
+  -version-info 5:3:0 \
   -no-undefined
 
 libtalermerchant_la_SOURCES = \
diff --git a/src/lib/merchant_api_get_config.c b/src/lib/merchant_api_get_config.c
index cf5147fe..9b501342 100644
--- a/src/lib/merchant_api_get_config.c
+++ b/src/lib/merchant_api_get_config.c
@@ -34,12 +34,12 @@
  * Which version of the Taler protocol is implemented
  * by this library?  Used to determine compatibility.
  */
-#define MERCHANT_PROTOCOL_CURRENT 15
+#define MERCHANT_PROTOCOL_CURRENT 16
 
 /**
  * How many configs are we backwards-compatible with?
  */
-#define MERCHANT_PROTOCOL_AGE 3
+#define MERCHANT_PROTOCOL_AGE 4
 
 /**
  * How many exchanges do we allow at most per merchant?