How to work with sequentially linked tables in Yii2 using ActiveRecord?

Question

MySQL

Please help with Yii2 and ActiveRecord.
For several days I have been trying to figure out how to work with multiple sequentially linked tables using ActiveRecord in Yii2.
Tables:
department
id
value
building
id
value
department_id (foreign key)
room
id
value
building_id (foreign key)
Here is the working SQL code:

SELECT department.value, room.id, room.value
FROM department
LEFT JOIN building ON department.id=building.department_id
LEFT JOIN room ON building.id=room.building_id
WHERE department.id = 7

How to implement this with ActiveRecord?
PS
If you need to join one table, then everything is simple.

Answer 1

Use a Gii generator and it will do everything for you. Department
model .

class Department extends \yii\db\ActiveRecord {
  /**
   * @return \yii\db\ActiveQuery
   */
  public function getBuildings() {
    return $this->hasMany(Building::className(), ['department_id' => 'id']);
  }
  // ...
}

Can receive:
Model Building .

class Building extends \yii\db\ActiveRecord {
  /**
   * @return \yii\db\ActiveQuery
   */
  public function getDepartment() {
    return $this->hasOne(Department::className(), ['id' => 'department_id']);
  }
  /**
   * @return \yii\db\ActiveQuery
   */
  public function getRooms() {
    return $this->hasMany(Room::className(), ['building_id' => 'id']);
  }
  // ...
}

May receive:

var_dump($building->department);
var_dump($building->rooms);

Room model .

class Room extends \yii\db\ActiveRecord {
  /**
   * @return \yii\db\ActiveQuery
   */
  public function getBuilding() {
    return $this->hasOne(Building::className(), ['id' => 'building_id']);
  }
  // ...
}

May receive:
var_dump($room->building);