public function testChangeHasOneRelationWithAnotherObject()
 {
     $dummy_a = new DummyModel();
     $dummy_b = new DummyModel();
     $dummy_a->save();
     $dummy_b->save();
     $dummy_a->children = $dummy_b;
     $dummy_b->children = $dummy_a;
     $this->assertTrue($dummy_a->save(), 'Dummy A could not be saved');
     $this->assertTrue($dummy_b->save(), 'Dummy B could not be saved');
     $dummy_c = new DummyModel();
     $dummy_a->children = $dummy_c;
     $this->assertTrue($dummy_a->save(), 'Dummy A could not be saved');
 }
 /**
  * @return \yii\db\ActiveQuery
  */
 public function getChildren()
 {
     return $this->hasOne(DummyModel::className(), ['id' => 'parent_id']);
 }