MDL-72723 logs: Add get_events_select_exists to the sql_reader interface

- Updates to log stores and backup helper to improve performance when
  checking if a course has been modified.
- This is a breaking change as it adds a new function on the sql_reader
  interface.

Co-authored-by: Kevin Pham <keevan.pham@gmail.com>

admin/tool/log/store/database/classes/log/store.php

@@ -262,6 +262,26 @@ class store implements \tool_log\log\writer, \core\log\sql_reader {
         return $this->extdb->count_records_select($dbtable, $selectwhere, $params);
     }
 
+    /**
+     * Get whether events are present for the given select clause.
+     *
+     * @param string $selectwhere select conditions.
+     * @param array $params params.
+     *
+     * @return bool Whether events available for the given conditions
+     */
+    public function get_events_select_exists(string $selectwhere, array $params): bool {
+        if (!$this->init()) {
+            return false;
+        }
+
+        if (!$dbtable = $this->get_config('dbtable')) {
+            return false;
+        }
+
+        return $this->extdb->record_exists_select($dbtable, $selectwhere, $params);
+    }
+
     /**
      * Get a config value for the store.
      *

admin/tool/log/store/legacy/classes/log/store.php

@@ -131,6 +131,29 @@ class store implements \tool_log\log\store, \core\log\sql_reader {
         return $events;
     }
 
+    /**
+     * Get whether events are present for the given select clause.
+     * @deprecated since Moodle 3.6 MDL-52953 - Please use supported log stores such as "standard" or "external" instead.
+     *
+     * @param string $selectwhere select conditions.
+     * @param array $params params.
+     *
+     * @return bool Whether events available for the given conditions
+     */
+    public function get_events_select_exists(string $selectwhere, array $params): bool {
+        global $DB;
+
+        // Replace the query with hardcoded mappings required for core.
+        list($selectwhere, $params) = self::replace_sql_legacy($selectwhere, $params);
+
+        try {
+            return $DB->record_exists_select('log', $selectwhere, $params);
+        } catch (\moodle_exception $ex) {
+            debugging("error converting legacy event data " . $ex->getMessage() . $ex->debuginfo, DEBUG_DEVELOPER);
+            return false;
+        }
+    }
+
     /**
      * Fetch records using given criteria returning a Traversable object.
      * @deprecated since Moodle 3.6 MDL-52953 - Please use supported log stores such as "standard" or "external" instead.

admin/tool/log/store/standard/classes/log/store.php

@@ -139,11 +139,32 @@ class store implements \tool_log\log\writer, \core\log\sql_internal_table_reader
         return $event;
     }
 
+    /**
+     * Get number of events present for the given select clause.
+     *
+     * @param string $selectwhere select conditions.
+     * @param array $params params.
+     *
+     * @return int Number of events available for the given conditions
+     */
     public function get_events_select_count($selectwhere, array $params) {
         global $DB;
         return $DB->count_records_select('logstore_standard_log', $selectwhere, $params);
     }
 
+    /**
+     * Get whether events are present for the given select clause.
+     *
+     * @param string $selectwhere select conditions.
+     * @param array $params params.
+     *
+     * @return bool Whether events available for the given conditions
+     */
+    public function get_events_select_exists(string $selectwhere, array $params): bool {
+        global $DB;
+        return $DB->record_exists_select('logstore_standard_log', $selectwhere, $params);
+    }
+
     public function get_internal_log_table_name() {
         return 'logstore_standard_log';
     }

admin/tool/log/store/standard/tests/store_test.php

@@ -80,6 +80,8 @@ class store_test extends \advanced_testcase {
 
         $logs = $DB->get_records('logstore_standard_log', array(), 'id ASC');
         $this->assertCount(0, $logs);
+        $exists = $store->get_events_select_exists('', array(), 'timecreated ASC', 0, 0);
+        $this->assertFalse($exists);
 
         $this->setCurrentTimeStart();
 
@@ -147,6 +149,8 @@ class store_test extends \advanced_testcase {
         $this->assertSame(3, $store->get_events_select_count('', array()));
         $events = $store->get_events_select('', array(), 'timecreated ASC', 0, 0); // Is actually sorted by "timecreated ASC, id ASC".
         $this->assertCount(3, $events);
+        $exists = $store->get_events_select_exists('', array(), 'timecreated ASC', 0, 0);
+        $this->assertTrue($exists);
         $resev1 = array_shift($events);
         array_shift($events);
         $resev2 = array_shift($events);

backup/util/helper/backup_cron_helper.class.php

@@ -790,7 +790,7 @@ abstract class backup_cron_automated_helper {
                 $where .= " and target <> 'course_backup'";
             }
 
-            if ($reader->get_events_select_count($where, $params)) {
+            if ($reader->get_events_select_exists($where, $params)) {
                 return true;
             }
         }

lib/classes/log/sql_reader.php

@@ -60,6 +60,16 @@ interface sql_reader extends reader {
      */
     public function get_events_select_count($selectwhere, array $params);
 
+    /**
+     * Get whether events are present for the given select clause.
+     *
+     * @param string $selectwhere select conditions.
+     * @param array $params params.
+     *
+     * @return bool Whether events available for the given conditions
+     */
+    public function get_events_select_exists(string $selectwhere, array $params): bool;
+
     /**
      * Fetch records using the given criteria returning an traversable list of events.
      *

lib/upgrade.txt

@@ -1,6 +1,12 @@
 This files describes API changes in core libraries and APIs,
 information provided here is intended especially for developers.
 
+=== 4.1 ===
+
+* For performance reasons, sql_reader interface has a new function get_events_select_exists() which determines whether
+  an event exists with the given criteria (see MDL-72723 for details).
+   - Breaking: 3rd party log readers implementing interface sql_reader will need to implement get_events_select_exists()
+
 === 4.0 ===
 
 * To better detect wrong floats (like, for example, unformatted, using local-dependent separators ones) a number of