How to Work with Many-To-Many Relations in Yii2

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

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

Many To Many relations Yii2

It's bad way because the making of that code in multiple models will make models dirtier. The better way is usage of a universal component that can manage relations in your models. For example yii2-many-to-many-behavior

Yii2 many-to-many model relation

This public $images; property should be renamed because it coincides with the name of relation getImages()

class Slider extends Sl
{
    const SCENARIO_CREATE = 'create';
    const SCENARIO_VIEW = 'view';
    const SCENARIO_UPDATE = 'update';

    public $images; // This should be renamed
    ...

YII2 how do i handle many to many relationships?

Method getCategories() returns ActiveQuery object instead of models. If you need to get an array of category models you must use magical property categories. For example:

var_dump($user->categories);

Many-to-many relation in yii2 activedataprovider

You can create two more relations like this

In category:

public function getProducts()
{
   return $this->hasMany(Product::className(), ['id' =>   'product_id'])->via("productCategories");
}

And in product:

public function getCategories()
{
  return $this->hasMany(Category::ClassName(), ['id' =>   'category_id'])->via("productCategories");
}

Then you can use it like this

$cats = Category::findOne(['slug1'=>$slug1]);
$dataProvider = new ActiveDataProvider([

    'query' => $query = $cats->getProducts(),
    'sort'=>array(
        'defaultOrder'=>['id' => SORT_ASC],
    ),
    'pagination' => [
        'pageSize' => 9,
    ],
]);

Yii 2 Filter many-to-many relation on a value in the junction table

I found in the documentation that you can add a callback to the viaTable() function that can be used to customize the join query. You can use it like this:

public function getAcceptedMembers() {
    return $this->hasMany(Member::className(), ['id' => 'member_id'])->viaTable('EventMemberConnection acceptedConnection', ['event_id' => 'id'], function($query){
        $query->where(['acceptedConnection.accepted' => 1]);
    });
}

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