diff --git a/framework/data/ActiveDataProvider.php b/framework/data/ActiveDataProvider.php
index 7f9d83ccc5..993bb9a1a3 100644
--- a/framework/data/ActiveDataProvider.php
+++ b/framework/data/ActiveDataProvider.php
@@ -56,12 +56,11 @@ use yii\di\Instance;
 class ActiveDataProvider extends BaseDataProvider
 {
     /**
-     * @var QueryInterface the query that is used to fetch data models and [[totalCount]]
-     * if it is not explicitly set.
+     * @var QueryInterface|null the query that is used to fetch data models and [[totalCount]] if it is not explicitly set.
      */
     public $query;
     /**
-     * @var string|callable the column that is used as the key of the data models.
+     * @var string|callable|null the column that is used as the key of the data models.
      * This can be either a column name, or a callable that returns the key value of a given data model.
      *
      * If this is not set, the following rules will be used to determine the keys of the data models:
@@ -73,8 +72,8 @@ class ActiveDataProvider extends BaseDataProvider
      */
     public $key;
     /**
-     * @var Connection|array|string the DB connection object or the application component ID of the DB connection.
-     * If not set, the default DB connection will be used.
+     * @var Connection|array|string|null the DB connection object or the application component ID of the DB connection.
+     * If set it overrides [[query]] default DB connection.
      * Starting from version 2.0.2, this can also be a configuration array for creating the object.
      */
     public $db;
@@ -82,13 +81,15 @@ class ActiveDataProvider extends BaseDataProvider
 
     /**
      * Initializes the DB connection component.
-     * This method will initialize the [[db]] property to make sure it refers to a valid DB connection.
+     * This method will initialize the [[db]] property (when set) to make sure it refers to a valid DB connection.
      * @throws InvalidConfigException if [[db]] is invalid.
      */
     public function init()
     {
         parent::init();
-        $this->db = Instance::ensure($this->db === null ? 'db' : $this->db, Connection::className());
+        if ($this->db !== null) {
+            $this->db = Instance::ensure($this->db, Connection::className());
+        }
     }
 
     /**
@@ -173,7 +174,7 @@ class ActiveDataProvider extends BaseDataProvider
     public function setSort($value)
     {
         parent::setSort($value);
-        if (($sort = $this->getSort()) !== false && $this->query instanceof ActiveQueryInterface) {
+        if ($this->query instanceof ActiveQueryInterface && ($sort = $this->getSort()) !== false) {
             /* @var $modelClass Model */
             $modelClass = $this->query->modelClass;
             $model = $modelClass::instance();
diff --git a/tests/framework/data/ActiveDataProviderCloningTest.php b/tests/framework/data/ActiveDataProviderCloningTest.php
index 836ce8151b..1027baf47c 100644
--- a/tests/framework/data/ActiveDataProviderCloningTest.php
+++ b/tests/framework/data/ActiveDataProviderCloningTest.php
@@ -8,21 +8,16 @@
 namespace yiiunit\framework\data;
 
 use yii\data\ActiveDataProvider;
-use yii\db\Connection;
 use yii\db\Query;
 use yiiunit\TestCase;
 
 class ActiveDataProviderCloningTest extends TestCase
 {
-
-    // Tests :
-
     public function testClone()
     {
         $queryFirst = new Query();
 
         $dataProviderFirst = new ActiveDataProvider([
-            'db' => new Connection(),
             'query' => $queryFirst
         ]);
 
@@ -33,4 +28,3 @@ class ActiveDataProviderCloningTest extends TestCase
         $this->assertNotSame($querySecond, $queryFirst);
     }
 }
-
diff --git a/tests/framework/data/ActiveDataProviderTest.php b/tests/framework/data/ActiveDataProviderTest.php
index d87f106a62..b496dcb96b 100644
--- a/tests/framework/data/ActiveDataProviderTest.php
+++ b/tests/framework/data/ActiveDataProviderTest.php
@@ -35,7 +35,6 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
     public function testActiveQuery()
     {
         $provider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => Order::find()->orderBy('id'),
         ]);
         $orders = $provider->getModels();
@@ -46,7 +45,6 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertEquals([1, 2, 3], $provider->getKeys());
 
         $provider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => Order::find(),
             'pagination' => [
                 'pageSize' => 2,
@@ -61,7 +59,6 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         /* @var $customer Customer */
         $customer = Customer::findOne(2);
         $provider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => $customer->getOrders(),
         ]);
         $orders = $provider->getModels();
@@ -71,7 +68,6 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertEquals([2, 3], $provider->getKeys());
 
         $provider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => $customer->getOrders(),
             'pagination' => [
                 'pageSize' => 1,
@@ -86,7 +82,6 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         /* @var $order Order */
         $order = Order::findOne(2);
         $provider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => $order->getItems(),
         ]);
         $items = $provider->getModels();
@@ -97,7 +92,6 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertEquals([3, 4, 5], $provider->getKeys());
 
         $provider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => $order->getItems(),
             'pagination' => [
                 'pageSize' => 2,
@@ -112,7 +106,6 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         /* @var $order Order */
         $order = Order::findOne(1);
         $provider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => $order->getBooks(),
         ]);
         $items = $provider->getModels();
@@ -121,7 +114,6 @@ abstract class ActiveDataProviderTest extends DatabaseTestCase
         $this->assertInstanceOf(Item::className(), $items[1]);
 
         $provider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => $order->getBooks(),
             'pagination' => [
                 'pageSize' => 1,
diff --git a/tests/framework/widgets/LinkSorterTest.php b/tests/framework/widgets/LinkSorterTest.php
index baf2221d06..8d607221e4 100644
--- a/tests/framework/widgets/LinkSorterTest.php
+++ b/tests/framework/widgets/LinkSorterTest.php
@@ -34,7 +34,6 @@ class LinkSorterTest extends DatabaseTestCase
     public function testLabelsSimple()
     {
         $dataProvider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => Order::find(),
             'models' => [new Order()],
             'totalCount' => 1,
@@ -59,7 +58,6 @@ class LinkSorterTest extends DatabaseTestCase
     public function testLabelsExplicit()
     {
         $dataProvider = new ActiveDataProvider([
-            'db' => $this->getConnection(),
             'query' => Order::find(),
             'models' => [new Order()],
             'totalCount' => 1,
@@ -88,7 +86,7 @@ class LinkSorterTest extends DatabaseTestCase
     public function testShouldTriggerInitEvent()
     {
         $initTriggered = false;
-        $linkSorter = new LinkSorter(
+        new LinkSorter(
             [
                 'sort' => [
                     'attributes' => ['total'],