diff --git a/classes/assess_type.php b/classes/assess_type.php
index 0ac8888..e144c6f 100644
--- a/classes/assess_type.php
+++ b/classes/assess_type.php
@@ -108,10 +108,9 @@ public static function is_summative(int $cmid): bool {
      */
     public static function is_locked(int $cmid): bool {
         global $DB;
-        if ($r = $DB->get_record('local_assess_type', ['cmid' => $cmid])) {
-            return $r->locked;
-        }
-        return false;
+        $record = $DB->get_record('local_assess_type', ['cmid' => $cmid], 'locked');
+
+        return (bool) ($record->locked ?? false);
     }
 
     /**
diff --git a/db/install.xml b/db/install.xml
index b7b3f2c..33b900f 100644
--- a/db/install.xml
+++ b/db/install.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-<XMLDB PATH="local/assess_type/db" VERSION="20240902" COMMENT="XMLDB file for UCL"
+<XMLDB PATH="local/assess_type/db" VERSION="20240913" COMMENT="XMLDB file for UCL"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:noNamespaceSchemaLocation="../../../lib/xmldb/xmldb.xsd"
 >
@@ -8,10 +8,10 @@
       <FIELDS>
         <FIELD NAME="id" TYPE="int" LENGTH="10" NOTNULL="true" SEQUENCE="true"/>
         <FIELD NAME="courseid" TYPE="int" LENGTH="10" NOTNULL="true" SEQUENCE="false" COMMENT="Foreign key of course id"/>
-        <FIELD NAME="cmid" TYPE="int" LENGTH="10" NOTNULL="false" SEQUENCE="false" COMMENT="Foreign key cm id"/>
-        <FIELD NAME="gradeitemid" TYPE="int" LENGTH="10" NOTNULL="false" SEQUENCE="false"/>
-        <FIELD NAME="type" TYPE="int" LENGTH="1" NOTNULL="false" SEQUENCE="false" COMMENT="The value of this datum"/>
-        <FIELD NAME="locked" TYPE="int" LENGTH="1" NOTNULL="false" SEQUENCE="false" COMMENT="Locked field"/>
+        <FIELD NAME="cmid" TYPE="int" LENGTH="10" NOTNULL="true" DEFAULT="0" SEQUENCE="false" COMMENT="Foreign key cm id"/>
+        <FIELD NAME="gradeitemid" TYPE="int" LENGTH="10" NOTNULL="true" DEFAULT="0" SEQUENCE="false"/>
+        <FIELD NAME="type" TYPE="int" LENGTH="1" NOTNULL="true" SEQUENCE="false" COMMENT="The value of this datum"/>
+        <FIELD NAME="locked" TYPE="int" LENGTH="1" NOTNULL="true" DEFAULT="0" SEQUENCE="false" COMMENT="Locked field"/>
       </FIELDS>
       <KEYS>
         <KEY NAME="primary" TYPE="primary" FIELDS="id"/>
diff --git a/db/upgrade.php b/db/upgrade.php
new file mode 100644
index 0000000..06043a8
--- /dev/null
+++ b/db/upgrade.php
@@ -0,0 +1,67 @@
+<?php
+// This file is part of Moodle - https://moodle.org/
+//
+// Moodle 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 of the License, or
+// (at your option) any later version.
+//
+// Moodle 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 Moodle.  If not, see <https://www.gnu.org/licenses/>.
+
+/**
+ * Plugin upgrade steps are defined here.
+ *
+ * @package     local_assess_type
+ * @category    upgrade
+ * @copyright   2024 onwards University College London {@link https://www.ucl.ac.uk/}
+ * @license     https://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @author      Alex Yeung <k.yeung@ucl.ac.uk>
+ */
+
+/**
+ * Execute local_assess_type upgrade from the given old version.
+ *
+ * @param int $oldversion
+ * @return bool
+ */
+function xmldb_local_assess_type_upgrade($oldversion) {
+    global $DB;
+    $dbman = $DB->get_manager();
+
+    if ($oldversion < 2024091300) {
+        $table = new xmldb_table('local_assess_type');
+
+        $field = new xmldb_field('cmid', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, '0', 'courseid');
+        // Launch change of nullability for field cmid.
+        $dbman->change_field_notnull($table, $field);
+        // Launch change of default for field cmid.
+        $dbman->change_field_default($table, $field);
+
+        $field = new xmldb_field('gradeitemid', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, '0', 'cmid');
+        // Launch change of nullability for field gradeitemid.
+        $dbman->change_field_notnull($table, $field);
+        // Launch change of default for field gradeitemid.
+        $dbman->change_field_default($table, $field);
+
+        $field = new xmldb_field('type', XMLDB_TYPE_INTEGER, '1', null, XMLDB_NOTNULL, null, null, 'gradeitemid');
+        // Launch change of nullability for field type.
+        $dbman->change_field_notnull($table, $field);
+
+        $field = new xmldb_field('locked', XMLDB_TYPE_INTEGER, '1', null, XMLDB_NOTNULL, null, '0', 'type');
+        // Launch change of nullability for field locked.
+        $dbman->change_field_notnull($table, $field);
+        // Launch change of default for field locked.
+        $dbman->change_field_default($table, $field);
+
+        // Assess_type savepoint reached.
+        upgrade_plugin_savepoint(true, 2024091300, 'local', 'assess_type');
+    }
+
+    return true;
+}
diff --git a/version.php b/version.php
index fa69475..dae8b9b 100644
--- a/version.php
+++ b/version.php
@@ -27,6 +27,6 @@
 
 $plugin->component = 'local_assess_type';
 $plugin->release = '1.0';
-$plugin->version = 2024080600; // YYYYMMDD.
+$plugin->version = 2024091300; // YYYYMMDD.
 $plugin->requires = 2023100900;
 $plugin->maturity = MATURITY_STABLE;