diff --git a/mod/quiz/classes/local/structure/slot_random.php b/mod/quiz/classes/local/structure/slot_random.php
index ebd89f14e3a..50ef17fed98 100644
--- a/mod/quiz/classes/local/structure/slot_random.php
+++ b/mod/quiz/classes/local/structure/slot_random.php
@@ -43,6 +43,11 @@ class slot_random {
      */
     protected $quiz = null;
 
+    /**
+     * @var \core_tag_tag[] List of tags for this slot.
+     */
+    protected $tags = [];
+
     /**
      * slot_random constructor.
      *
@@ -52,9 +57,8 @@ class slot_random {
         $this->record = new \stdClass();
 
         $properties = array(
-                'id', 'slot', 'quizid', 'page', 'requireprevious',
-                'questionid', 'questioncategoryid', 'includingsubcategories',
-                'tags', 'maxmark');
+            'id', 'slot', 'quizid', 'page', 'requireprevious', 'questionid',
+            'questioncategoryid', 'includingsubcategories', 'maxmark');
 
         foreach ($properties as $property) {
             if (isset($slotrecord->$property)) {
@@ -95,6 +99,29 @@ class slot_random {
         $this->record->quizid = $quiz->id;
     }
 
+    /**
+     * Set some tags for this quiz slot.
+     *
+     * @param \core_tag_tag[] $tags
+     */
+    public function set_tags($tags) {
+        $this->tags = [];
+        foreach ($tags as $tag) {
+            // We use $tag->id as the key for the array so not only it handles duplicates of the same tag being given,
+            // but also it is consistent with the behaviour of set_tags_by_id() below.
+            $this->tags[$tag->id] = $tag;
+        }
+    }
+
+    /**
+     * Set some tags for this quiz slot. This function uses tag ids to find tags.
+     *
+     * @param int[] $tagids
+     */
+    public function set_tags_by_id($tagids) {
+        $this->tags = \core_tag_tag::get_bulk($tagids, 'id, name');
+    }
+
     /**
      * Inserts the quiz slot at the $page page.
      * It is required to call this function if you are building a quiz slot object from scratch.
@@ -151,6 +178,19 @@ class slot_random {
         }
 
         $this->record->id = $DB->insert_record('quiz_slots', $this->record);
+
+        if (!empty($this->tags)) {
+            $recordstoinsert = [];
+            foreach ($this->tags as $tag) {
+                $recordstoinsert[] = (object)[
+                    'slotid' => $this->record->id,
+                    'tagid' => $tag->id,
+                    'tagname' => $tag->name
+                ];
+            }
+            $DB->insert_records('quiz_slot_tags', $recordstoinsert);
+        }
+
         $trans->allow_commit();
     }
 }
\ No newline at end of file
diff --git a/mod/quiz/locallib.php b/mod/quiz/locallib.php
index 7b529562ecc..d3d29632e8b 100644
--- a/mod/quiz/locallib.php
+++ b/mod/quiz/locallib.php
@@ -2189,18 +2189,10 @@ function quiz_add_random_questions($quiz, $addonpage, $categoryid, $number,
     $catcontext = context::instance_by_id($category->contextid);
     require_capability('moodle/question:useall', $catcontext);
 
-    $tags = [];
+    $tags = \core_tag_tag::get_bulk($tagids, 'id, name');
     $tagstrings = [];
-    foreach ($tagids as $tagid) {
-        if ($tag = core_tag_tag::get($tagid, 'id,name')) {
-            $tags[] = [
-                    'id' => $tagid,
-                    'name' => $tag->name
-            ];
-            $tagstrings[] = "{$tagid},{$tag->name}";
-        } else if (!empty($tagid)) {
-            print_error('invalidtagid', 'mod_quiz');
-        }
+    foreach ($tags as $tag) {
+        $tagstrings[] = "{$tag->id},{$tag->name}";
     }
 
     // Find existing random questions in this category that are
@@ -2239,11 +2231,11 @@ function quiz_add_random_questions($quiz, $addonpage, $categoryid, $number,
         $randomslotdata->questionid = $question->id;
         $randomslotdata->questioncategoryid = $categoryid;
         $randomslotdata->includingsubcategories = $includesubcategories ? 1 : 0;
-        $randomslotdata->tags = json_encode($tags);
         $randomslotdata->maxmark = 1;
 
         $randomslot = new \mod_quiz\local\structure\slot_random($randomslotdata);
         $randomslot->set_quiz($quiz);
+        $randomslot->set_tags($tags);
         $randomslot->insert($addonpage);
     }
 }
diff --git a/mod/quiz/tests/local_structure_slot_random_test.php b/mod/quiz/tests/local_structure_slot_random_test.php
new file mode 100755
index 00000000000..a9c1cd5fbfd
--- /dev/null
+++ b/mod/quiz/tests/local_structure_slot_random_test.php
@@ -0,0 +1,413 @@
+<?php
+// This file is part of Moodle - http://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 <http://www.gnu.org/licenses/>.
+
+/**
+ * Unit tests for the {@link \mod_quiz\local\structure\slot_random} class.
+ *
+ * @package    mod_quiz
+ * @category   test
+ * @copyright  2018 Shamim Rezaie <shamim@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+/**
+ * Class mod_quiz_local_structure_slot_random_test
+ * Class for tests related to the {@link \mod_quiz\local\structure\slot_random} class.
+ *
+ * @copyright  2018 Shamim Rezaie <shamim@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class mod_quiz_local_structure_slot_random_test extends advanced_testcase {
+    /**
+     * Constructor test.
+     */
+    public function test_constructor() {
+        global $SITE;
+
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        // Create a quiz.
+        $quizgenerator = $this->getDataGenerator()->get_plugin_generator('mod_quiz');
+        $quiz = $quizgenerator->create_instance(array('course' => $SITE->id, 'questionsperpage' => 3, 'grade' => 100.0));
+
+        // Create a question category in the system context.
+        $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
+        $category = $questiongenerator->create_question_category();
+
+        // Create a random question without adding it to a quiz.
+        // We don't want to use quiz_add_random_questions because that itself, instantiates an object from the slot_random class.
+        $form = new stdClass();
+        $form->category = $category->id . ',' . $category->contextid;
+        $form->includesubcategories = true;
+        $form->fromtags = [];
+        $form->defaultmark = 1;
+        $form->hidden = 1;
+        $form->stamp = make_unique_id_code();
+        $question = new stdClass();
+        $question->qtype = 'random';
+        $question = question_bank::get_qtype('random')->save_question($question, $form);
+
+        $randomslotdata = new stdClass();
+        $randomslotdata->quizid = $quiz->id;
+        $randomslotdata->questionid = $question->id;
+        $randomslotdata->questioncategoryid = $category->id;
+        $randomslotdata->includingsubcategories = 1;
+        $randomslotdata->maxmark = 1;
+
+        $randomslot = new \mod_quiz\local\structure\slot_random($randomslotdata);
+
+        $rc = new ReflectionClass('\mod_quiz\local\structure\slot_random');
+        $rcp = $rc->getProperty('record');
+        $rcp->setAccessible(true);
+        $record = $rcp->getValue($randomslot);
+
+        $this->assertEquals($quiz->id, $record->quizid);
+        $this->assertEquals($question->id, $record->questionid);
+        $this->assertEquals($category->id, $record->questioncategoryid);
+        $this->assertEquals(1, $record->includingsubcategories);
+        $this->assertEquals(1, $record->maxmark);
+    }
+
+    public function test_get_quiz_quiz() {
+        global $SITE, $DB;
+
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        // Create a quiz.
+        $quizgenerator = $this->getDataGenerator()->get_plugin_generator('mod_quiz');
+        $quiz = $quizgenerator->create_instance(array('course' => $SITE->id, 'questionsperpage' => 3, 'grade' => 100.0));
+
+        // Create a question category in the system context.
+        $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
+        $category = $questiongenerator->create_question_category();
+
+        quiz_add_random_questions($quiz, 0, $category->id, 1, false);
+
+        // Get the random question's id. It is at the first slot.
+        $questionid = $DB->get_field('quiz_slots', 'questionid', array('quizid' => $quiz->id, 'slot' => 1));
+
+        $randomslotdata = new stdClass();
+        $randomslotdata->quizid = $quiz->id;
+        $randomslotdata->questionid = $questionid;
+        $randomslotdata->questioncategoryid = $category->id;
+        $randomslotdata->includingsubcategories = 1;
+        $randomslotdata->maxmark = 1;
+
+        $randomslot = new \mod_quiz\local\structure\slot_random($randomslotdata);
+
+        // The create_instance had injected an additional cmid propery to the quiz. Let's remove that.
+        unset($quiz->cmid);
+
+        $this->assertEquals($quiz, $randomslot->get_quiz());
+    }
+
+    public function test_set_quiz() {
+        global $SITE, $DB;
+
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        // Create a quiz.
+        $quizgenerator = $this->getDataGenerator()->get_plugin_generator('mod_quiz');
+        $quiz = $quizgenerator->create_instance(array('course' => $SITE->id, 'questionsperpage' => 3, 'grade' => 100.0));
+
+        // Create a question category in the system context.
+        $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
+        $category = $questiongenerator->create_question_category();
+
+        quiz_add_random_questions($quiz, 0, $category->id, 1, false);
+
+        // Get the random question's id. It is at the first slot.
+        $questionid = $DB->get_field('quiz_slots', 'questionid', array('quizid' => $quiz->id, 'slot' => 1));
+
+        $randomslotdata = new stdClass();
+        $randomslotdata->quizid = $quiz->id;
+        $randomslotdata->questionid = $questionid;
+        $randomslotdata->questioncategoryid = $category->id;
+        $randomslotdata->includingsubcategories = 1;
+        $randomslotdata->maxmark = 1;
+
+        $randomslot = new \mod_quiz\local\structure\slot_random($randomslotdata);
+
+        // The create_instance had injected an additional cmid propery to the quiz. Let's remove that.
+        unset($quiz->cmid);
+
+        $randomslot->set_quiz($quiz);
+
+        $rc = new ReflectionClass('\mod_quiz\local\structure\slot_random');
+        $rcp = $rc->getProperty('quiz');
+        $rcp->setAccessible(true);
+        $quizpropery = $rcp->getValue($randomslot);
+
+        $this->assertEquals($quiz, $quizpropery);
+    }
+
+    private function setup_for_test_tags($tagnames) {
+        global $SITE, $DB;
+
+        // Create a quiz.
+        $quizgenerator = $this->getDataGenerator()->get_plugin_generator('mod_quiz');
+        $quiz = $quizgenerator->create_instance(array('course' => $SITE->id, 'questionsperpage' => 3, 'grade' => 100.0));
+
+        // Create a question category in the system context.
+        $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
+        $category = $questiongenerator->create_question_category();
+
+        quiz_add_random_questions($quiz, 0, $category->id, 1, false);
+
+        // Get the random question's id. It is at the first slot.
+        $questionid = $DB->get_field('quiz_slots', 'questionid', array('quizid' => $quiz->id, 'slot' => 1));
+
+        $randomslotdata = new stdClass();
+        $randomslotdata->quizid = $quiz->id;
+        $randomslotdata->questionid = $questionid;
+        $randomslotdata->questioncategoryid = $category->id;
+        $randomslotdata->includingsubcategories = 1;
+        $randomslotdata->maxmark = 1;
+
+        $randomslot = new \mod_quiz\local\structure\slot_random($randomslotdata);
+
+        // Create tags.
+        foreach ($tagnames as $tagname) {
+            $tagrecord = array(
+                'isstandard' => 1,
+                'flag' => 0,
+                'rawname' => $tagname,
+                'description' => $tagname . ' desc'
+            );
+            $tags[$tagname] = $this->getDataGenerator()->create_tag($tagrecord);
+        }
+
+        return array($randomslot, $tags);
+    }
+
+    public function test_set_tags() {
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        list($randomslot, $tags) = $this->setup_for_test_tags(['foo', 'bar']);
+        $randomslot->set_tags([$tags['foo'], $tags['bar']]);
+
+        $rc = new ReflectionClass('\mod_quiz\local\structure\slot_random');
+        $rcp = $rc->getProperty('tags');
+        $rcp->setAccessible(true);
+        $tagspropery = $rcp->getValue($randomslot);
+
+        $this->assertEquals([
+            $tags['foo']->id => $tags['foo'],
+            $tags['bar']->id => $tags['bar'],
+        ], $tagspropery);
+    }
+
+    public function test_set_tags_twice() {
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        list($randomslot, $tags) = $this->setup_for_test_tags(['foo', 'bar', 'baz']);
+
+        // Set tags for the first time.
+        $randomslot->set_tags([$tags['foo'], $tags['bar']]);
+        // Now set the tags again.
+        $randomslot->set_tags([$tags['baz']]);
+
+        $rc = new ReflectionClass('\mod_quiz\local\structure\slot_random');
+        $rcp = $rc->getProperty('tags');
+        $rcp->setAccessible(true);
+        $tagspropery = $rcp->getValue($randomslot);
+
+        $this->assertEquals([
+            $tags['baz']->id => $tags['baz'],
+        ], $tagspropery);
+    }
+
+    public function test_set_tags_duplicates() {
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        list($randomslot, $tags) = $this->setup_for_test_tags(['foo', 'bar', 'baz']);
+
+        $randomslot->set_tags([$tags['foo'], $tags['bar'], $tags['foo']]);
+
+        $rc = new ReflectionClass('\mod_quiz\local\structure\slot_random');
+        $rcp = $rc->getProperty('tags');
+        $rcp->setAccessible(true);
+        $tagspropery = $rcp->getValue($randomslot);
+
+        $this->assertEquals([
+            $tags['foo']->id => $tags['foo'],
+            $tags['bar']->id => $tags['bar'],
+        ], $tagspropery);
+    }
+
+    public function test_set_tags_by_id() {
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        list($randomslot, $tags) = $this->setup_for_test_tags(['foo', 'bar', 'baz']);
+
+        $randomslot->set_tags_by_id([$tags['foo']->id, $tags['bar']->id]);
+
+        $rc = new ReflectionClass('\mod_quiz\local\structure\slot_random');
+        $rcp = $rc->getProperty('tags');
+        $rcp->setAccessible(true);
+        $tagspropery = $rcp->getValue($randomslot);
+
+        // The set_tags_by_id function only retrieves id and name fields of the tag object.
+        $this->assertCount(2, $tagspropery);
+        $this->assertArrayHasKey($tags['foo']->id, $tagspropery);
+        $this->assertArrayHasKey($tags['bar']->id, $tagspropery);
+        $this->assertEquals(
+                (object)['id' => $tags['foo']->id, 'name' => $tags['foo']->name],
+                $tagspropery[$tags['foo']->id]->to_object()
+        );
+        $this->assertEquals(
+                (object)['id' => $tags['bar']->id, 'name' => $tags['bar']->name],
+                $tagspropery[$tags['bar']->id]->to_object()
+        );
+    }
+
+    public function test_set_tags_by_id_twice() {
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        list($randomslot, $tags) = $this->setup_for_test_tags(['foo', 'bar', 'baz']);
+
+        // Set tags for the first time.
+        $randomslot->set_tags_by_id([$tags['foo']->id, $tags['bar']->id]);
+        // Now set the tags again.
+        $randomslot->set_tags_by_id([$tags['baz']->id]);
+
+        $rc = new ReflectionClass('\mod_quiz\local\structure\slot_random');
+        $rcp = $rc->getProperty('tags');
+        $rcp->setAccessible(true);
+        $tagspropery = $rcp->getValue($randomslot);
+
+        // The set_tags_by_id function only retrieves id and name fields of the tag object.
+        $this->assertCount(1, $tagspropery);
+        $this->assertArrayHasKey($tags['baz']->id, $tagspropery);
+        $this->assertEquals(
+                (object)['id' => $tags['baz']->id, 'name' => $tags['baz']->name],
+                $tagspropery[$tags['baz']->id]->to_object()
+        );
+    }
+
+    public function test_set_tags_by_id_duplicates() {
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        list($randomslot, $tags) = $this->setup_for_test_tags(['foo', 'bar', 'baz']);
+
+        $randomslot->set_tags_by_id([$tags['foo']->id, $tags['bar']->id], $tags['foo']->id);
+
+        $rc = new ReflectionClass('\mod_quiz\local\structure\slot_random');
+        $rcp = $rc->getProperty('tags');
+        $rcp->setAccessible(true);
+        $tagspropery = $rcp->getValue($randomslot);
+
+        // The set_tags_by_id function only retrieves id and name fields of the tag object.
+        $this->assertCount(2, $tagspropery);
+        $this->assertArrayHasKey($tags['foo']->id, $tagspropery);
+        $this->assertArrayHasKey($tags['bar']->id, $tagspropery);
+        $this->assertEquals(
+                (object)['id' => $tags['foo']->id, 'name' => $tags['foo']->name],
+                $tagspropery[$tags['foo']->id]->to_object()
+        );
+        $this->assertEquals(
+                (object)['id' => $tags['bar']->id, 'name' => $tags['bar']->name],
+                $tagspropery[$tags['bar']->id]->to_object()
+        );
+    }
+
+    public function test_insert() {
+        global $SITE, $DB;
+
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        // Create a quiz.
+        $quizgenerator = $this->getDataGenerator()->get_plugin_generator('mod_quiz');
+        $quiz = $quizgenerator->create_instance(array('course' => $SITE->id, 'questionsperpage' => 3, 'grade' => 100.0));
+
+        // Create a question category in the system context.
+        $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
+        $category = $questiongenerator->create_question_category();
+
+        // Create a random question without adding it to a quiz.
+        $form = new stdClass();
+        $form->category = $category->id . ',' . $category->contextid;
+        $form->includesubcategories = true;
+        $form->fromtags = [];
+        $form->defaultmark = 1;
+        $form->hidden = 1;
+        $form->stamp = make_unique_id_code();
+        $question = new stdClass();
+        $question->qtype = 'random';
+        $question = question_bank::get_qtype('random')->save_question($question, $form);
+
+        // Prepare 2 tags.
+        $tagrecord = array(
+            'isstandard' => 1,
+            'flag' => 0,
+            'rawname' => 'foo',
+            'description' => 'foo desc'
+        );
+        $footag = $this->getDataGenerator()->create_tag($tagrecord);
+        $tagrecord = array(
+            'isstandard' => 1,
+            'flag' => 0,
+            'rawname' => 'bar',
+            'description' => 'bar desc'
+        );
+        $bartag = $this->getDataGenerator()->create_tag($tagrecord);
+
+        $randomslotdata = new stdClass();
+        $randomslotdata->quizid = $quiz->id;
+        $randomslotdata->questionid = $question->id;
+        $randomslotdata->questioncategoryid = $category->id;
+        $randomslotdata->includingsubcategories = 1;
+        $randomslotdata->maxmark = 1;
+
+        // Insert the random question to the quiz.
+        $randomslot = new \mod_quiz\local\structure\slot_random($randomslotdata);
+        $randomslot->set_tags([$footag, $bartag]);
+        $randomslot->insert(1); // Put the question on the first page of the quiz.
+
+        // Get the random question's quiz_slot. It is at the first slot.
+        $quizslot = $DB->get_record('quiz_slots', array('quizid' => $quiz->id, 'slot' => 1));
+        // Get the random question's tags from quiz_slot_tags. It is at the first slot.
+        $quizslottags = $DB->get_records('quiz_slot_tags', array('slotid' => $quizslot->id));
+
+        $this->assertEquals($question->id, $quizslot->questionid);
+        $this->assertEquals($category->id, $quizslot->questioncategoryid);
+        $this->assertEquals(1, $quizslot->includingsubcategories);
+        $this->assertEquals(1, $quizslot->maxmark);
+
+        $this->assertCount(2, $quizslottags);
+        $this->assertEquals(
+                [
+                    ['tagid' => $footag->id, 'tagname' => $footag->name],
+                    ['tagid' => $bartag->id, 'tagname' => $bartag->name]
+                ],
+                array_map(function($slottag) {
+                    return ['tagid' => $slottag->tagid, 'tagname' => $slottag->tagname];
+                }, $quizslottags),
+                '', 0.0, 10, true);
+    }
+}
\ No newline at end of file
diff --git a/tag/classes/tag.php b/tag/classes/tag.php
index c41f80f9260..52dfd34b1ec 100644
--- a/tag/classes/tag.php
+++ b/tag/classes/tag.php
@@ -209,7 +209,7 @@ class core_tag_tag {
     }
 
     /**
-     * Simple function to just return a single tag object by its id
+     * Simple function to just return an array of tag objects by their ids
      *
      * @param    int[]  $ids
      * @param    string $returnfields which fields do we want returned from table {tag}.