How do I work with many-to-many relations in Yii2

Question

For example in one-to-many due to documentation (http://www.yiiframework.com/doc-2.0/guide-db-active-record.html#relational-data) you can link two models in this way (one-many = company-zone):

$defaultZone = new Zone;
$defaultZone->name = Zone::DEFAULT_ZONE;
$company->link('zones', $defaultZone);

But how it works for many-to-many relations when you have transit table like tbl_user_market(user_id, market_id)?

Answer 1

When using a junction table for many-to-many relations, you have to

1. Define the relations
2. Link the two models together

In the User model define the following relation function:

public function getMarkets() {
    return $this->hasMany(Market::className(), ['id' => 'market_id'])
      ->viaTable('tbl_user_market', ['user_id' => 'id']);
}

In the Market model define the following relation function:

public function getUsers() {
    return $this->hasMany(User::className(), ['id' => 'user_id'])
      ->viaTable('tbl_user_market', ['market_id' => 'id']);
}

And finally, after saving both models, link them together:

$user = new User;
$user->name = 'Foo';
$user->save();

$market = new Market;
$market->name = 'Bar';
$market->save();

$user->link('markets', $market);

The call to link() will populate the junction table.

Reference: http://www.yiiframework.com/doc-2.0/yii-db-baseactiverecord.html#link()-detail