diff --git a/extensions/mongodb/ActiveRecord.php b/extensions/mongodb/ActiveRecord.php
index ce8ac81747..7bcf593687 100644
--- a/extensions/mongodb/ActiveRecord.php
+++ b/extensions/mongodb/ActiveRecord.php
@@ -37,7 +37,7 @@ abstract class ActiveRecord extends BaseActiveRecord
 	 * For example, to change the status to be 1 for all customers whose status is 2:
 	 *
 	 * ~~~
-	 * Customer::updateAll(['status' => 1], ['status' = 2]);
+	 * Customer::updateAll(['status' => 1], ['status' => 2]);
 	 * ~~~
 	 *
 	 * @param array $attributes attribute values (name-value pairs) to be saved into the collection
@@ -78,7 +78,7 @@ abstract class ActiveRecord extends BaseActiveRecord
 	 * For example, to delete all customers whose status is 3:
 	 *
 	 * ~~~
-	 * Customer::deleteAll('status = 3');
+	 * Customer::deleteAll(['status' => 3]);
 	 * ~~~
 	 *
 	 * @param array $condition description of the objects to delete.
@@ -88,10 +88,6 @@ abstract class ActiveRecord extends BaseActiveRecord
 	 */
 	public static function deleteAll($condition = [], $options = [])
 	{
-		$options['w'] = 1;
-		if (!array_key_exists('multiple', $options)) {
-			$options['multiple'] = true;
-		}
 		return static::getCollection()->remove($condition, $options);
 	}
 
@@ -237,8 +233,7 @@ abstract class ActiveRecord extends BaseActiveRecord
 				$values[$key] = isset($currentAttributes[$key]) ? $currentAttributes[$key] : null;
 			}
 		}
-		$collection = static::getCollection();
-		$newId = $collection->insert($values);
+		$newId = static::getCollection()->insert($values);
 		$this->setAttribute('_id', $newId);
 		foreach ($values as $name => $value) {
 			$this->setOldAttribute($name, $value);
@@ -348,4 +343,4 @@ abstract class ActiveRecord extends BaseActiveRecord
 		}
 		return $this->collectionName() === $record->collectionName() && (string)$this->getPrimaryKey() === (string)$record->getPrimaryKey();
 	}
-}
+}
\ No newline at end of file
diff --git a/extensions/mongodb/Collection.php b/extensions/mongodb/Collection.php
index 21411e7dd5..38144bc1e5 100644
--- a/extensions/mongodb/Collection.php
+++ b/extensions/mongodb/Collection.php
@@ -259,6 +259,18 @@ class Collection extends Object
 		return $this->mongoCollection->find($this->buildCondition($condition), $fields);
 	}
 
+	/**
+	 * Returns a a single document.
+	 * @param array $condition query condition
+	 * @param array $fields fields to be selected
+	 * @return array|null the single document. Null is returned if the query results in nothing.
+	 * @see http://www.php.net/manual/en/mongocollection.findone.php
+	 */
+	public function findOne($condition = [], $fields = [])
+	{
+		return $this->mongoCollection->findOne($this->buildCondition($condition), $fields);
+	}
+
 	/**
 	 * Inserts new data into collection.
 	 * @param array|object $data data to be inserted.
@@ -372,11 +384,12 @@ class Collection extends Object
 	 * @param array $options list of options in format: optionName => optionValue.
 	 * @return integer|boolean number of updated documents or whether operation was successful.
 	 * @throws Exception on failure.
+	 * @see http://www.php.net/manual/en/mongocollection.remove.php
 	 */
 	public function remove($condition = [], $options = [])
 	{
 		$condition = $this->buildCondition($condition);
-		$options = array_merge(['w' => 1, 'multiple' => true], $options);
+		$options = array_merge(['w' => 1, 'justOne' => false], $options);
 		$token = $this->composeLogToken('remove', [$condition, $options]);
 		Yii::info($token, __METHOD__);
 		try {
@@ -522,7 +535,7 @@ class Collection extends Object
 	 * Argument will be automatically cast to [[\MongoCode]].
 	 * @param string|array $out output collection name. It could be a string for simple output
 	 * ('outputCollection'), or an array for parametrized output (['merge' => 'outputCollection']).
-     * You can pass ['inline' => true] to fetch the result at once without temporary collection usage.
+	 * You can pass ['inline' => true] to fetch the result at once without temporary collection usage.
 	 * @param array $condition criteria for including a document in the aggregation.
 	 * @param array $options additional optional parameters to the mapReduce command. Valid options include:
 	 *  - sort - array - key to sort the input documents. The sort key must be in an existing index for this collection.
diff --git a/extensions/mongodb/Connection.php b/extensions/mongodb/Connection.php
index ab8e30fe90..e79bfcb949 100644
--- a/extensions/mongodb/Connection.php
+++ b/extensions/mongodb/Connection.php
@@ -72,6 +72,11 @@ use Yii;
  */
 class Connection extends Component
 {
+	/**
+	 * @event Event an event that is triggered after a DB connection is established
+	 */
+	const EVENT_AFTER_OPEN = 'afterOpen';
+
 	/**
 	 * @var string host:port
 	 *
@@ -233,6 +238,7 @@ class Connection extends Component
 					$options['db'] = $this->defaultDatabaseName;
 				}
 				$this->mongoClient = new \MongoClient($this->dsn, $options);
+				$this->initConnection();
 				Yii::endProfile($token, __METHOD__);
 			} catch (\Exception $e) {
 				Yii::endProfile($token, __METHOD__);
@@ -253,4 +259,14 @@ class Connection extends Component
 			$this->_databases = [];
 		}
 	}
+
+	/**
+	 * Initializes the DB connection.
+	 * This method is invoked right after the DB connection is established.
+	 * The default implementation triggers an [[EVENT_AFTER_OPEN]] event.
+	 */
+	protected function initConnection()
+	{
+		$this->trigger(self::EVENT_AFTER_OPEN);
+	}
 }
\ No newline at end of file
diff --git a/extensions/mongodb/Session.php b/extensions/mongodb/Session.php
index f2ce8b375d..9b630ccc65 100644
--- a/extensions/mongodb/Session.php
+++ b/extensions/mongodb/Session.php
@@ -91,28 +91,22 @@ class Session extends \yii\web\Session
 		parent::regenerateID(false);
 		$newID = session_id();
 
-		$query = new Query;
-		$row = $query->from($this->sessionCollection)
-			->where(['id' => $oldID])
-			->one($this->db);
-		if ($row !== false) {
+		$collection = $this->db->getCollection($this->sessionCollection);
+		$row = $collection->findOne(['id' => $oldID]);
+		if ($row !== null) {
 			if ($deleteOldSession) {
-				$this->db->getCollection($this->sessionCollection)
-					->update(['_id' => $row['_id']], ['id' => $newID]);
+				$collection->update(['id' => $oldID], ['id' => $newID]);
 			} else {
 				unset($row['_id']);
 				$row['id'] = $newID;
-				$this->db->getCollection($this->sessionCollection)
-					->insert($row);
+				$collection->insert($row);
 			}
 		} else {
 			// shouldn't reach here normally
-			$this->db->getCollection($this->sessionCollection)
-				->insert([
-					'id' => $newID,
-					'expire' => time() + $this->getTimeout(),
-					'data' => '',
-				]);
+			$collection->insert([
+				'id' => $newID,
+				'expire' => time() + $this->getTimeout()
+			]);
 		}
 	}
 
@@ -124,15 +118,15 @@ class Session extends \yii\web\Session
 	 */
 	public function readSession($id)
 	{
-		$query = new Query;
-		$row = $query->select(['data'])
-			->from($this->sessionCollection)
-			->where([
+		$collection = $this->db->getCollection($this->sessionCollection);
+		$doc = $collection->findOne(
+			[
+				'id' => $id,
 				'expire' => ['$gt' => time()],
-				'id' => $id
-			])
-			->one($this->db);
-		return $row === false ? '' : $row['data'];
+			],
+			['data' => 1, '_id' => 0]
+		);
+		return isset($doc['data']) ? $doc['data'] : '';
 	}
 
 	/**
@@ -147,23 +141,15 @@ class Session extends \yii\web\Session
 		// exception must be caught in session write handler
 		// http://us.php.net/manual/en/function.session-set-save-handler.php
 		try {
-			$expire = time() + $this->getTimeout();
-			$query = new Query;
-			$exists = $query->select(['id'])
-				->from($this->sessionCollection)
-				->where(['id' => $id])
-				->one($this->db);
-			if ($exists === false) {
-				$this->db->getCollection($this->sessionCollection)
-					->insert([
-						'id' => $id,
-						'data' => $data,
-						'expire' => $expire,
-					]);
-			} else {
-				$this->db->getCollection($this->sessionCollection)
-					->update(['id' => $id], ['data' => $data, 'expire' => $expire]);
-			}
+			$this->db->getCollection($this->sessionCollection)->update(
+				['id' => $id],
+				[
+					'id' => $id,
+					'data' => $data,
+					'expire' => time() + $this->getTimeout(),
+				],
+				['upsert' => true]
+			);
 		} catch (\Exception $e) {
 			if (YII_DEBUG) {
 				echo $e->getMessage();
@@ -182,8 +168,10 @@ class Session extends \yii\web\Session
 	 */
 	public function destroySession($id)
 	{
-		$this->db->getCollection($this->sessionCollection)
-			->remove(['id' => $id]);
+		$this->db->getCollection($this->sessionCollection)->remove(
+			['id' => $id],
+			['justOne' => true]
+		);
 		return true;
 	}
 
@@ -196,9 +184,7 @@ class Session extends \yii\web\Session
 	public function gcSession($maxLifetime)
 	{
 		$this->db->getCollection($this->sessionCollection)
-			->remove([
-				'expire' => ['$lt' => time()]
-			]);
+			->remove(['expire' => ['$lt' => time()]]);
 		return true;
 	}
 }
\ No newline at end of file