# Data Providers ¶

In the Pagination and Sorting sections, we have described how to allow end users to choose a particular page of data to display and sort them by some columns. Because the task of paginating and sorting data is very common, Yii provides a set of data provider classes to encapsulate it.

A data provider is a class implementing yii\data\DataProviderInterface. It mainly supports retrieving paginated and sorted data. It is usually used to work with data widgets so that end users can interactively paginate and sort data.

The following data provider classes are included in the Yii releases:

- yii\data\ActiveDataProvider: uses yii\db\Query or yii\db\ActiveQuery to query data from databases and return them in terms of arrays or Active Record instances.
- yii\data\SqlDataProvider: executes a SQL statement and returns database data as arrays.
- yii\data\ArrayDataProvider: takes a big array and returns a slice of it based on the paginating and sorting specifications.

The usage of all these data providers share the following common pattern:

    // create the data provider by configuring its pagination and sort properties
    $provider = new XyzDataProvider([
        'pagination' => [...],
        'sort' => [...],
    ]);

    // retrieves paginated and sorted data
    $models = $provider->getModels();

    // get the number of data items in the current page
    $count = $provider->getCount();

    // get the total number of data items across all pages
    $totalCount = $provider->getTotalCount();

You specify the pagination and sorting behaviors of a data provider by configuring its pagination and sort properties which correspond to the configurations for yii\data\Pagination and yii\data\Sort, respectively. You may also configure them to be `false` to disable pagination and/or sorting features.

Data widgets, such as yii\grid\GridView, have a property named `dataProvider` which can take a data provider instance and display the data it provides. For example,

    echo yii\grid\GridView::widget([
        'dataProvider' => $dataProvider,
    ]);

These data providers mainly vary in the way how the data source is specified. In the following subsections, we will explain the detailed usage of each of these data providers.

## Active Data Provider ¶

To use yii\data\ActiveDataProvider, you should configure its query property. It can take either a yii\db\Query or yii\db\ActiveQuery object. If the former, the data returned will be arrays; if the latter, the data returned can be either arrays or Active Record instances. For example,

    use yii\data\ActiveDataProvider;

    $query = Post::find()->where(['status' => 1]);

    $provider = new ActiveDataProvider([
        'query' => $query,
        'pagination' => [
            'pageSize' => 10,
        ],
        'sort' => [
            'defaultOrder' => [
                'created_at' => SORT_DESC,
                'title' => SORT_ASC,
            ]
        ],
    ]);

    // returns an array of Post objects
    $posts = $provider->getModels();

If `$query` in the above example is created using the following code, then the data provider will return raw arrays.

    use yii\db\Query;

    $query = (new Query())->from('post')->where(['status' => 1]);

> Note: If a query already specifies the `orderBy` clause, the new ordering instructions given by end users (through the `sort` configuration) will be appended to the existing `orderBy` clause. Any existing `limit` and `offset` clauses will be overwritten by the pagination request from end users (through the `pagination` configuration).

By default, yii\data\ActiveDataProvider uses the `db` application component as the database connection. You may use a different database connection by configuring the yii\data\ActiveDataProvider::$db property.

## SQL Data Provider ¶

yii\data\SqlDataProvider works with a raw SQL statement which is used to fetch the needed data. Based on the specifications of sort and pagination, the provider will adjust the `ORDER BY` and `LIMIT` clauses of the SQL statement accordingly to fetch only the requested page of data in the desired order.

To use yii\data\SqlDataProvider, you should specify the sql property as well as the totalCount property. For example,

    use yii\data\SqlDataProvider;

    $count = Yii::$app->db->createCommand('
        SELECT COUNT(*) FROM post WHERE status=:status
    ', [':status' => 1])->queryScalar();

    $provider = new SqlDataProvider([
        'sql' => 'SELECT * FROM post WHERE status=:status',
        'params' => [':status' => 1],
        'totalCount' => $count,
        'pagination' => [
            'pageSize' => 10,
        ],
        'sort' => [
            'attributes' => [
                'title',
                'view_count',
                'created_at',
            ],
        ],
    ]);

    // returns an array of data rows
    $models = $provider->getModels();

> Info: The totalCount property is required only if you need to paginate the data. This is because the SQL statement specified via sql will be modified by the provider to return only the currently requested page of data. The provider still needs to know the total number of data items in order to correctly calculate the number of pages available.

## Array Data Provider ¶

yii\data\ArrayDataProvider is best used when working with a big array. The provider allows you to return a page of the array data sorted by one or multiple columns. To use yii\data\ArrayDataProvider, you should specify the allModels property as the big array. Elements in the big array can be either associative arrays (e.g. query results of DAO) or objects (e.g. Active Record instances). For example,

    use yii\data\ArrayDataProvider;

    $data = [
        ['id' => 1, 'name' => 'name 1', ...],
        ['id' => 2, 'name' => 'name 2', ...],
        ...
        ['id' => 100, 'name' => 'name 100', ...],
    ];

    $provider = new ArrayDataProvider([
        'allModels' => $data,
        'pagination' => [
            'pageSize' => 10,
        ],
        'sort' => [
            'attributes' => ['id', 'name'],
        ],
    ]);

    // get the rows in the currently requested page
    $rows = $provider->getModels();

> Note: Compared to Active Data Provider and SQL Data Provider, array data provider is less efficient because it requires loading all data into the memory.

## Working with Data Keys ¶

When using the data items returned by a data provider, you often need to identify each data item with a unique key. For example, if the data items represent customer information, you may want to use the customer ID as the key for each customer data. Data providers can return a list of such keys corresponding with the data items returned by yii\data\DataProviderInterface::getModels(). For example,

    use yii\data\ActiveDataProvider;

    $query = Post::find()->where(['status' => 1]);

    $provider = new ActiveDataProvider([
        'query' => $query,
    ]);

    // returns an array of Post objects
    $posts = $provider->getModels();

    // returns the primary key values corresponding to $posts
    $ids = $provider->getKeys();

In the above example, because you provide to yii\data\ActiveDataProvider an yii\db\ActiveQuery object, it is intelligent enough to return primary key values as the keys. You may also explicitly specify how the key values should be calculated by configuring yii\data\ActiveDataProvider::$key with a column name or a callable calculating key values. For example,

    // use "slug" column as key values
    $provider = new ActiveDataProvider([
        'query' => Post::find(),
        'key' => 'slug',
    ]);

    // use the result of md5(id) as key values
    $provider = new ActiveDataProvider([
        'query' => Post::find(),
        'key' => function ($model) {
            return md5($model->id);
        }
    ]);

## Creating Custom Data Provider ¶

To create your own custom data provider classes, you should implement yii\data\DataProviderInterface. An easier way is to extend from yii\data\BaseDataProvider which allows you to focus on the core data provider logic. In particular, you mainly need to implement the following methods:

- prepareModels(): prepares the data models that will be made available in the current page and returns them as an array.
- prepareKeys(): accepts an array of currently available data models and returns keys associated with them.
- prepareTotalCount: returns a value indicating the total number of data models in the data provider.

Below is an example of a data provider that reads CSV data efficiently:

    <?php
    use yii\data\BaseDataProvider;

    class CsvDataProvider extends BaseDataProvider
    {
        /**
         * @var string name of the CSV file to read
         */
        public $filename;

        /**
         * @var string|callable name of the key column or a callable returning it
         */
        public $key;

        /**
         * @var SplFileObject
         */
        protected $fileObject; // SplFileObject is very convenient for seeking to particular line in a file

        /**
         * {@inheritdoc}
         */
        public function init()
        {
            parent::init();

            // open file
            $this->fileObject = new SplFileObject($this->filename);
        }

        /**
         * {@inheritdoc}
         */
        protected function prepareModels()
        {
            $models = [];
            $pagination = $this->getPagination();

            if ($pagination === false) {
                // in case there's no pagination, read all lines
                while (!$this->fileObject->eof()) {
                    $models[] = $this->fileObject->fgetcsv();
                    $this->fileObject->next();
                }
            } else {
                // in case there's pagination, read only a single page
                $pagination->totalCount = $this->getTotalCount();
                $this->fileObject->seek($pagination->getOffset());
                $limit = $pagination->getLimit();

                for ($count = 0; $count < $limit; ++$count) {
                    $models[] = $this->fileObject->fgetcsv();
                    $this->fileObject->next();
                }
            }

            return $models;
        }

        /**
         * {@inheritdoc}
         */
        protected function prepareKeys($models)
        {
            if ($this->key !== null) {
                $keys = [];

                foreach ($models as $model) {
                    if (is_string($this->key)) {
                        $keys[] = $model[$this->key];
                    } else {
                        $keys[] = call_user_func($this->key, $model);
                    }
                }

                return $keys;
            }

            return array_keys($models);
        }

        /**
         * {@inheritdoc}
         */
        protected function prepareTotalCount()
        {
            $count = 0;

            while (!$this->fileObject->eof()) {
                $this->fileObject->next();
                ++$count;
            }

            return $count;
        }
    }

## Filtering Data Providers using Data Filters ¶

While you can build conditions for active data provider manually as described in Filtering Data and Separate Filter Form sections of data widgets guide, Yii has data filters that are very useful if you need flexible filter conditions. Data filters could be used as follows:

    $filter = new ActiveDataFilter([
        'searchModel' => 'app\models\PostSearch'
    ]);

    $filterCondition = null;

    // You may load filters from any source. For example,
    // if you prefer JSON in request body,
    // use Yii::$app->request->getBodyParams() below:
    if ($filter->load(\Yii::$app->request->get())) {
        $filterCondition = $filter->build();
        if ($filterCondition === false) {
            // Serializer would get errors out of it
            return $filter;
        }
    }

    $query = Post::find();
    if ($filterCondition !== null) {
        $query->andWhere($filterCondition);
    }

    return new ActiveDataProvider([
        'query' => $query,
    ]);

`PostSearch` model serves the purpose of defining which properties and values are allowed for filtering:

    use yii\base\Model;

    class PostSearch extends Model
    {
        public $id;
        public $title;

        public function rules()
        {
            return [
                ['id', 'integer'],
                ['title', 'string', 'min' => 2, 'max' => 200],
            ];
        }
    }

Data filters are quite flexible. You may customize how conditions are built and which operators are allowed. For details check API docs on yii\data\DataFilter.