MDL-43736 Events: event->contextinstanceid should be used where possible

While restoring event context might not be present (deleted)
So before using context api's check context or use event properties

lib/classes/event/assessable_submitted.php

@@ -59,7 +59,7 @@ abstract class assessable_submitted extends \core\event\base {
      * @return void
      */
     protected function validate_data() {
-        if (!$this->context->contextlevel === CONTEXT_MODULE) {
+        if (!$this->contextlevel === CONTEXT_MODULE) {
             throw new \coding_exception('Content level must be CONTEXT_MODULE.');
         }
     }

lib/classes/event/assessable_uploaded.php

@@ -66,7 +66,7 @@ abstract class assessable_uploaded extends \core\event\base {
      * @return void
      */
     protected function validate_data() {
-        if (!$this->context->contextlevel === CONTEXT_MODULE) {
+        if (!$this->contextlevel === CONTEXT_MODULE) {
             throw new \coding_exception('Content level must be CONTEXT_MODULE.');
         } else if (!isset($this->other['pathnamehashes']) || !is_array($this->other['pathnamehashes'])) {
             throw new \coding_exception('pathnamehashes must be set in $other and must be an array.');

lib/classes/event/base.php

@@ -355,7 +355,7 @@ abstract class base implements \IteratorAggregate {
         if (isset($this->context)) {
             return $this->context;
         }
-        $this->context = \context::instance_by_id($this->data['contextid'], false);
+        $this->context = \context::instance_by_id($this->data['contextid'], IGNORE_MISSING);
         return $this->context;
     }
 

lib/classes/event/blog_association_created.php

@@ -69,8 +69,8 @@ class blog_association_created extends \core\event\base {
      * @return string
      */
     public function get_description() {
-        return "Blog association added between entry id $this->other['blogid'] and $this->other['associatetype'] with id
-                $this->other['associateid']";
+        return "Blog association added between entry id {$this->other['blogid']} and {$this->other['associatetype']} with id
+                {$this->other['associateid']}";
     }
 
     /**

lib/classes/event/comment_created.php

@@ -79,7 +79,12 @@ abstract class comment_created extends \core\event\base {
      * @return \moodle_url
      */
     public function get_url() {
-        return $this->context->get_url();
+        $context = $this->get_context();
+        if ($context) {
+            return $context->get_url();
+        } else {
+            return null;
+        }
     }
 
     /**

lib/classes/event/comment_deleted.php

@@ -79,7 +79,12 @@ abstract class comment_deleted extends \core\event\base {
      * @return \moodle_url
      */
     public function get_url() {
-        return $this->context->get_url();
+        $context = $this->get_context();
+        if ($context) {
+            return $context->get_url();
+        } else {
+            return null;
+        }
     }
 
     /**

lib/classes/event/comments_viewed.php

@@ -72,6 +72,11 @@ abstract class comments_viewed extends \core\event\base {
      * @return \moodle_url
      */
     public function get_url() {
-        return $this->context->get_url();
+        $context = $this->get_context();
+        if ($context) {
+            return $context->get_url();
+        } else {
+            return null;
+        }
     }
 }

lib/classes/event/course_module_instance_list_viewed.php

@@ -105,7 +105,7 @@ abstract class course_module_instance_list_viewed extends base{
      * @return void
      */
     protected function validate_data() {
-        if ($this->context->contextlevel !== CONTEXT_COURSE) {
+        if ($this->contextlevel !== CONTEXT_COURSE) {
             throw new \coding_exception('The context must be a course level context.');
         }
     }

lib/classes/event/course_module_viewed.php

@@ -72,7 +72,7 @@ abstract class course_module_viewed extends base {
      * @return \moodle_url
      */
     public function get_url() {
-        return new \moodle_url("/mod/$this->objecttable/view.php", array('id' => $this->context->instanceid));
+        return new \moodle_url("/mod/$this->objecttable/view.php", array('id' => $this->contextinstanceid));
     }
 
     /**
@@ -81,8 +81,8 @@ abstract class course_module_viewed extends base {
      * @return array|null
      */
     protected function get_legacy_logdata() {
-        return array($this->courseid, $this->objecttable, 'view', 'view.php?id=' . $this->context->instanceid, $this->objectid,
-                     $this->context->instanceid);
+        return array($this->courseid, $this->objecttable, 'view', 'view.php?id=' . $this->contextinstanceid, $this->objectid,
+                     $this->contextinstanceid);
     }
 
     /**