MDL-39723 Remove unnecessary queries for COURSE, SITE

course/format/lib.php

@@ -235,7 +235,7 @@ abstract class format_base {
             return null;
         }
         if ($this->course === false) {
-            $this->course = $DB->get_record('course', array('id' => $this->courseid));
+            $this->course = get_course($this->courseid);
             $options = $this->get_format_options();
             foreach ($options as $optionname => $optionvalue) {
                 if (!isset($this->course->$optionname)) {

lib/datalib.php

@@ -556,6 +556,30 @@ function get_site() {
     }
 }
 
+/**
+ * Gets a course object from database. If the course id corresponds to an
+ * already-loaded $COURSE or $SITE object, then the loaded object will be used,
+ * saving a database query.
+ *
+ * If it reuses an existing object, by default the object will be cloned. This
+ * means you can modify the object safely without affecting other code.
+ *
+ * @param int $courseid Course id
+ * @param bool $clone If true (default), makes a clone of the record
+ * @return stdClass A course object
+ * @throws dml_exception If not found in database
+ */
+function get_course($courseid, $clone = true) {
+    global $DB, $COURSE, $SITE;
+    if (!empty($COURSE->id) && $COURSE->id == $courseid) {
+        return $clone ? clone($COURSE) : $COURSE;
+    } else if (!empty($SITE->id) && $SITE->id == $courseid) {
+        return $clone ? clone($SITE) : $SITE;
+    } else {
+        return $DB->get_record('course', array('id' => $courseid), '*', MUST_EXIST);
+    }
+}
+
 /**
  * Returns list of courses, for whole site, or category
  *

lib/tests/datalib_test.php

@@ -267,4 +267,30 @@ class datalib_testcase extends advanced_testcase {
         get_admins(); // This should make just one query.
         $this->assertEquals($odlread+1, $DB->perf_get_reads());
     }
+
+    public function test_get_course() {
+        global $DB, $PAGE, $SITE;
+
+        $this->resetAfterTest(true);
+
+        // First test course will be current course ($COURSE).
+        $course1obj = $this->getDataGenerator()->create_course(array('shortname' => 'FROGS'));
+        $PAGE->set_course($course1obj);
+
+        // Second test course is not current course.
+        $course2obj = $this->getDataGenerator()->create_course(array('shortname' => 'ZOMBIES'));
+
+        // Check it does not make any queries when requesting the $COURSE/$SITE
+        $before = $DB->perf_get_queries();
+        $result = get_course($course1obj->id);
+        $this->assertEquals($before, $DB->perf_get_queries());
+        $this->assertEquals('FROGS', $result->shortname);
+        $result = get_course($SITE->id);
+        $this->assertEquals($before, $DB->perf_get_queries());
+
+        // Check it makes 1 query to request other courses.
+        $result = get_course($course2obj->id);
+        $this->assertEquals('ZOMBIES', $result->shortname);
+        $this->assertEquals($before + 1, $DB->perf_get_queries());
+    }
 }

lib/upgrade.txt

@@ -1,6 +1,11 @@
 This files describes API changes in core libraries and APIs,
 information provided here is intended especially for developers.
 
+=== 2.5.1 ===
+
+* New get_course() function for use when obtaining the course record from database. Will
+  reuse existing $COURSE or $SITE globals if possible to improve performance.
+
 === 2.5 ===
 
 * The database drivers (moodle_database and subclasses) aren't using anymore the ::columns property