MDL-69572 mod_book : add bookid index to book_chapters

mod/book/db/install.xml

 <?xml version="1.0" encoding="UTF-8" ?>
-<XMLDB PATH="mod/book/db" VERSION="20120515" COMMENT="XMLDB file for Moodle mod_book"
+<XMLDB PATH="mod/book/db" VERSION="20200907" COMMENT="XMLDB file for Moodle mod_book"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:noNamespaceSchemaLocation="../../../lib/xmldb/xmldb.xsd"
 >
@@ -39,6 +39,9 @@
       <KEYS>
         <KEY NAME="primary" TYPE="primary" FIELDS="id"/>
       </KEYS>
+      <INDEXES>
+        <INDEX NAME="bookid" UNIQUE="false" FIELDS="bookid"/>
+      </INDEXES>
     </TABLE>
   </TABLES>
 </XMLDB>

mod/book/db/upgrade.php

@@ -30,7 +30,9 @@ defined('MOODLE_INTERNAL') || die;
  * @return bool always true
  */
 function xmldb_book_upgrade($oldversion) {
-    global $CFG;
+    global $CFG, $DB;
+
+    $dbman = $DB->get_manager();
 
     // Automatically generated Moodle v3.5.0 release upgrade line.
     // Put any upgrade step following this.
@@ -47,5 +49,14 @@ function xmldb_book_upgrade($oldversion) {
     // Automatically generated Moodle v3.9.0 release upgrade line.
     // Put any upgrade step following this.
 
+    if ($oldversion < 2021052501) {
+        $table = new xmldb_table('book_chapters');
+        $index = new xmldb_index('bookid', XMLDB_INDEX_NOTUNIQUE, ['bookid']);
+        if (!$dbman->index_exists($table, $index)) {
+            $dbman->add_index($table, $index);
+        }
+        upgrade_mod_savepoint(true, 2021052501, 'book');
+    }
+
     return true;
 }

mod/book/version.php

@@ -25,6 +25,6 @@
 defined('MOODLE_INTERNAL') || die;
 
 $plugin->component = 'mod_book'; // Full name of the plugin (used for diagnostics)
-$plugin->version   = 2021052500; // The current module version (Date: YYYYMMDDXX)
+$plugin->version   = 2021052501; // The current module version (Date: YYYYMMDDXX)
 $plugin->requires  = 2021052500; // Requires this Moodle version
 $plugin->cron      = 0;          // Period for cron to check this module (secs)