To retrieve data using Yii models, utilize Active Record methods and query building. 1. Define a model class extending yii\db\ActiveRecord and specify the mapped table via tableName(). 2. Use findOne() to fetch a single record by primary key or condition. 3. Retrieve multiple records with find()->all() or findAll() combined with where clauses. 4. Build complex queries using where, andWhere, orderBy, limit, and parameter binding for security. 5. Define relations like hasMany() to access related data and use with() for eager loading to optimize performance.

When you need to retrieve data from the database using Yii models, the framework offers a clean and object-oriented way to do it. Instead of writing raw SQL queries, you work with Active Record classes that map to your database tables.

Understanding Yii Active Record Basics

In Yii, each model class typically extends yii\db\ActiveRecord, which gives you access to built-in methods for querying, inserting, updating, and deleting records. The first step is to make sure your model correctly maps to a database table. You can do this by overriding the tableName() method:

public static function tableName()
{
    return 'your_table_name';
}

Once that's set up, you can start retrieving data using methods like find(), which returns a query builder instance you can chain conditions on.

Retrieving Single or Multiple Records

You’ll often want to fetch either one record or a list of records. Here’s how you can do both:

• Retrieve a single record
  Use findOne() when you know there should be only one result (like searching by primary key or unique field):

  $model = ModelName::findOne($id);

  Or use conditions:

  $model = ModelName::findOne(['name' => 'John']);

• Retrieve multiple records
  Use find()->all() or findAll():

  $models = ModelName::find()->where(['status' => 1])->all();
  // or
  $models = ModelName::findAll(['status' => 1]);

Keep in mind that findOne() returns a single model instance or null, while find()->all() returns an array of models (which could be empty).

Querying with Conditions and Filters

Yii makes it easy to build complex queries using a fluent interface. You can add where clauses, sorting, limits, and more:

• Use basic conditionals:

  ModelName::find()->where(['>', 'age', 30])->all();

• Chain conditions:

  ModelName::find()
      ->where(['status' => 1])
      ->andWhere(['>', 'created_at', strtotime('-7 days')])
      ->orderBy('name')
      ->limit(10)
      ->all();

If you're working with dynamic input, consider using parameter binding to prevent SQL injection:

ModelName::find()->where('status = :status', [':status' => $status])->all();

This approach keeps your code secure and readable.

Using Relations Between Models

If your data involves multiple tables, Yii allows you to define relations inside your models. For example, if a User has many Orders, you can define a relation called getOrders() in your User model:

public function getOrders()
{
    return $this->hasMany(Order::class, ['user_id' => 'id']);
}

Then you can access related data like this:

$user = User::findOne(1);
$orders = $user->orders; // automatically fetches orders for that user

To avoid N 1 query issues, use eager loading with with():

$users = User::find()->with('orders')->all();

This loads all users and their related orders in just two queries instead of one per user.

That’s how you retrieve data using Yii models — through Active Record methods, query building, and defining relationships between models. It’s straightforward once you understand how the pieces fit together.

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