Yii2: Multiple inverse relations to same model?

Question

How do I handle multiple inverse relations pointing to the same active record? For example:

class Bicycle extends ActiveRecord {

    public function getFrontWheel() {
        return $this
            ->hasOne(Wheel::class, ['id' => 'front_wheel_id'])
            ->inverseOf('bicycles');
    }

    public function getRearWheel() {
        return $this
            ->hasOne(Wheel::class, ['id' => 'rear_wheel_id'])
            ->inverseOf('bicycles');
    }

}

class Wheel extends ActiveRecord {

    public function getBicycles() {
        return $this
            ->hasMany(Bicycle::class, ['???' => 'id'])
            ->inverseOf('??????');
    }

}

What can I do here? I critically need the inverse relations.

mae · Accepted Answer · 2021-05-11T07:06:53.367

Here is my own solution. Key points:

It all boils down to proper naming.
Inverse relations are bijective! In other words, every relation always has to have its own unique mirror relation on the other end.

class Bicycle extends ActiveRecord {

    public function getFrontWheel() {
        return $this
            ->hasOne(Wheel::class, ['id' => 'front_wheel_id'])
            ->inverseOf('frontWheelBicycles');
    }

    public function getRearWheel() {
        return $this
            ->hasOne(Wheel::class, ['id' => 'rear_wheel_id'])
            ->inverseOf('rearWheelBicycles');
    }

}

class Wheel extends ActiveRecord {

    public function getFrontWheelBicycles() {
        return $this
            ->hasMany(Bicycle::class, ['front_wheel_id' => 'id'])
            ->inverseOf('frontWheel');
    }

    public function getRearWheelBicycles() {
        return $this
            ->hasMany(Bicycle::class, ['rear_wheel_id' => 'id'])
            ->inverseOf('rearWheel');
    }

}

score -1 · Answer 2 · answered Apr 28 '21 at 06:54

i would suggest to do the following:

create two new classes:

class FrontWheel extends Wheel {
class RearWheel extends Wheel {

in new classes you can set easily the relation.

How to instantiate the correct class? There is a method in ActiveRecord instantiate() where you can write your logic which wheel class need to be created.

class Wheel extends ActiveRecord {
...

  public static function instantiate ( $row ) {
      if($row['type'] === 'RearWheel') {
           return new RealWheel();
      }
      ...

  }

full code:

class Bicycle extends ActiveRecord
{

    public function getFrontWheel()
    {
        return $this
            ->hasOne(Wheel::class, ['id' => 'front_wheel_id'])
            ->inverseOf('bicycles');
    }

    public function getRearWheel()
    {
        return $this
            ->hasOne(Wheel::class, ['id' => 'rear_wheel_id'])
            ->inverseOf('bicycles');
    }

}

abstract class Wheel extends ActiveRecord
{

    public static function instantiate($row)
    {
        if ($row['type'] === 'RearWheel') {
            return new RealWheel();
        }
        if ($row['type'] === 'FrontWheel') {
            return new FrontWheel();
        }
        
        throw new InvalidConfigException();
    }

    abstract public function getBicycles();
}

class RealWheel extends Wheel
{

    public function getBicycles()
    {
        return $this
            ->hasMany(Bicycle::class, ['rear_wheel_id' => 'id'])
            ->inverseOf('rearWheel');
    }

}

class FrontWheel extends Wheel
{

    public function getBicycles()
    {
        return $this
            ->hasMany(Bicycle::class, ['front_wheel_id' => 'id'])
            ->inverseOf('frontWheel');
    }

}

Interesting idea but it won't work. The wheels cannot have a "`type`" property, because they must be usable in either location (rear or front) without any modification. — mae, Apr 28 '21 at 07:14
Hi, if you cannot use type, you could query your db inside instantiate method where that id belongs, if it belongs to a front_wheel_id then you can instantate the front wheel class. I know it is an extra query, i think that is needed in your case. Think about this: Can you tell from a wheel without context (bike) whether it's a front or rear wheel? — Papp Péter, Apr 28 '21 at 07:43
Indeed, you cannot and you *should not* be able to. A wheel is a wheel. — mae, Apr 28 '21 at 07:45
So what do you think about querying for it in instantiate method? — Papp Péter, Apr 28 '21 at 07:54
That sounds like a performance hit, which defeats the whole purpose of inverse relations. Either way, I've found an elegant solution. I will post my answer in a couple of days unless someone proposes something better. — mae, Apr 28 '21 at 08:09

Yii2: Multiple inverse relations to same model?

2 Answers2