Question

I’m building a web application using Yii framework, and i’m quite new to it.
I have 3 db tables. One stores users, the second products, and the third is a relationship table that stores user_id, product_id and more info like the time the product was bought.

I configured a MANY_MANY relationship, and have no problem to get all the products the user has bought. However I can’t figure out how can I get the extra info from the relationship table?

Thank you

Answer 1

If your association holds additional data, you can declare itself as a class Purchase and add these relationships:

class User extends CActiveRecord
{
  public function relations()
  {
    return array(
      'purchases' => array(self::HAS_MANY, 'Purchase', 'user_id'),
      // Products purchased by this user
      'products' => array(
        self::HAS_MANY, 'Product', 'product_id',
        'through' => 'purchases',
      ),
    );
  }
}

class Purchase extends CActiveRecord
{
  // You need to add this, since every purchase is uniquely identified 
  // by user and product. Surrogate 'id' key is also fine
  public function primaryKey()
  {
    return array('user_id', 'product_id');
  }

  public function relations()
  {
    return array(
      'user' => array(self::BELONGS_TO, 'User', 'user_id'),
      'product' => array(self::BELONGS_TO, 'Product', 'product_id'),
    );
  }
}

Remove remaining MANY_MANY relationships from User and Product models. Note the usage of through relationship. Fetching data might look like this:

$users = User::model()->with('purchases.product')->findAll();
foreach ($users as $user) {
  echo $user->username . "<br>";
  echo 'Purchases<br>';
  foreach ($user->purchases as $purchase) {
    echo "Date: {$purchase->purchased_at}<br>";
    echo "Product: {$purchase->product->name} <br>";
  }
  echo '<hr>';
}

This will perform only one query from User table joining on another two tables. Also User::model()->with('products') will efficiently find user(s) with products they bought. Your DB scheme can remain the same, except you’ll need to add composite primary key in the association table.

See this article in the Yii wiki for a detailed explanation.