diff --git a/mod/assign/db/upgrade.php b/mod/assign/db/upgrade.php
index f24b0a772f6..20b7b915366 100644
--- a/mod/assign/db/upgrade.php
+++ b/mod/assign/db/upgrade.php
@@ -124,20 +124,20 @@ function xmldb_assign_upgrade($oldversion) {
 
         // Define field to be added to assign.
         $table = new xmldb_table('assign');
-        $field = new xmldb_field('teamsubmission', XMLDB_TYPE_INTEGER, '2', XMLDB_UNSIGNED,
+        $field = new xmldb_field('teamsubmission', XMLDB_TYPE_INTEGER, '2', null,
                                  XMLDB_NOTNULL, null, '0', 'cutoffdate');
 
         // Conditionally launch add field.
         if (!$dbman->field_exists($table, $field)) {
             $dbman->add_field($table, $field);
         }
-        $field = new xmldb_field('requireallteammemberssubmit', XMLDB_TYPE_INTEGER, '2', XMLDB_UNSIGNED,
+        $field = new xmldb_field('requireallteammemberssubmit', XMLDB_TYPE_INTEGER, '2', null,
                                  XMLDB_NOTNULL, null, '0', 'teamsubmission');
         // Conditionally launch add field.
         if (!$dbman->field_exists($table, $field)) {
             $dbman->add_field($table, $field);
         }
-        $field = new xmldb_field('teamsubmissiongroupingid', XMLDB_TYPE_INTEGER, '10', XMLDB_UNSIGNED,
+        $field = new xmldb_field('teamsubmissiongroupingid', XMLDB_TYPE_INTEGER, '10', null,
                                  XMLDB_NOTNULL, null, '0', 'requireallteammemberssubmit');
         // Conditionally launch add field.
         if (!$dbman->field_exists($table, $field)) {
@@ -149,7 +149,7 @@ function xmldb_assign_upgrade($oldversion) {
             $dbman->add_index($table, $index);
         }
         $table = new xmldb_table('assign_submission');
-        $field = new xmldb_field('groupid', XMLDB_TYPE_INTEGER, '10', XMLDB_UNSIGNED, XMLDB_NOTNULL, null, '0', 'status');
+        $field = new xmldb_field('groupid', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, '0', 'status');
         // Conditionally launch add field.
         if (!$dbman->field_exists($table, $field)) {
             $dbman->add_field($table, $field);
@@ -158,32 +158,41 @@ function xmldb_assign_upgrade($oldversion) {
     }
     if ($oldversion < 2012082400) {
 
-        // Define field to be added to assign
+        // Define table assign_user_mapping to be created
         $table = new xmldb_table('assign_user_mapping');
 
+        // Adding fields to table assign_user_mapping
         $table->add_field('id', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, XMLDB_SEQUENCE, null);
-        $table->add_field('assignment', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, null);
-        $table->add_field('userid', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, null);
+        $table->add_field('assignment', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, '0');
+        $table->add_field('userid', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, '0');
 
+        // Adding keys to table assign_user_mapping
         $table->add_key('primary', XMLDB_KEY_PRIMARY, array('id'));
-        $table->add_key('userid', XMLDB_KEY_FOREIGN, array('userid'), 'user', array('id'));
         $table->add_key('assignment', XMLDB_KEY_FOREIGN, array('assignment'), 'assign', array('id'));
+        $table->add_key('user', XMLDB_KEY_FOREIGN, array('userid'), 'user', array('id'));
 
+        // Conditionally launch create table for assign_user_mapping
         if (!$dbman->table_exists($table)) {
             $dbman->create_table($table);
         }
 
+        // Define field blindmarking to be added to assign
         $table = new xmldb_table('assign');
-        $field = new xmldb_field('blindmarking', XMLDB_TYPE_INTEGER, '2', XMLDB_UNSIGNED, XMLDB_NOTNULL, null, '0', 'teamsubmissiongroupingid');
+        $field = new xmldb_field('blindmarking', XMLDB_TYPE_INTEGER, '2', null, XMLDB_NOTNULL, null, '0', 'teamsubmissiongroupingid');
+
         if (!$dbman->field_exists($table, $field)) {
             $dbman->add_field($table, $field);
         }
 
+        // Define field revealidentities to be added to assign
         $table = new xmldb_table('assign');
-        $field = new xmldb_field('revealidentities', XMLDB_TYPE_INTEGER, '2', XMLDB_UNSIGNED, XMLDB_NOTNULL, null, '0', 'blindmarking');
+        $field = new xmldb_field('revealidentities', XMLDB_TYPE_INTEGER, '2', null, XMLDB_NOTNULL, null, '0', 'blindmarking');
+
         if (!$dbman->field_exists($table, $field)) {
             $dbman->add_field($table, $field);
         }
+
+        // assign savepoint reached
         upgrade_mod_savepoint(true, 2012082400, 'assign');
     }