Prevent errors because of faulty DB records

Previous versions introduced records with groupid=0 into the
ratingallocate_ch_gengroups table which caused problems with the
groups/choices synchronization/allocation feature. This fix deals with
the faulty records by deleting them and also handling them defensively
during record retrieval.

However, the root cause of these faulty records has not been fixed
extensively. This has to be investigated further.

Fixes: #330
References: #308, #316, #330

Author: dlmsr

classes/ratingallocate.php

@@ -1550,7 +1550,19 @@ public function synchronize_allocation_and_grouping() {
 
         // Fix for github bug issue #316. Delete bad dataset with groupingid=0 after backup and restore without groups/groupings.
         $where = "ratingallocateid = $this->ratingallocateid AND groupingid = 0";
-        $DB->delete_records_select(this_db\ratingallocate_groupings::TABLE, $where);
+        $this->db->delete_records_select(this_db\ratingallocate_groupings::TABLE, $where);
+
+        /* Delete records with invalid group ids introduced via faulty
+         * backup/restore process.
+         *
+         * FIXME: Do not introduce records with groupid = 0 during
+         * backup/restore
+         */
+        $this->db->delete_records(
+            this_db\ratingallocate_ch_gengroups::TABLE,
+            ['groupid' => 0]
+        );
+
         // Search if there is already a grouping from us.
         $where = "ratingallocateid = $this->ratingallocateid AND groupingid <> 0";
         if (!$groupingids = $this->db->get_record_select(this_db\ratingallocate_groupings::TABLE, $where, [], 'groupingid')) {
@@ -1619,8 +1631,10 @@ public function synchronize_allocation_and_grouping() {
             $choiceid = $allocation->choiceid;
             $userid = $allocation->userid;
             // Get the group corresponding to the choiceid.
-            $groupids = $this->db->get_record(
+            $groupids = $this->db->get_record_select(
                 this_db\ratingallocate_ch_gengroups::TABLE,
+                // Filter out records with groupip=0 which might exists because of backup/restore.
+                'choiceid = :choiceid AND groupid <> 0',
                 ['choiceid' => $choiceid],
                 'groupid'
             );