# Intra-data source Relationships

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This is the official documentation of the `forestadmin/laravel-forestadmin` v2+ and `forestadmin/symfony-forestadmin` PHP agents.
{% endhint %}

We've seen that when building data sources, collections must fulfill the contract they defined [when declaring their capabilities](https://docs.forestadmin.com/developer-guide-agents-php/data-sources/custom/translation/capabilities).

The same is also true for [Intra-data source relationships](https://docs.forestadmin.com/developer-guide-agents-php/data-sources/custom/structure#relationships) which are declared on the structure of a collection: declared relations must be handled when processing `filters`, `projection`, and `aggregations`.

## In practice

`one-to-many` and `many-to-many` relationships do not require additional work: Forest Admin will automatically call the destination collection with a valid filter.

On the other hand, `many-to-one` and `one-to-one` relationships require the implementer to make all fields from the target collection available on the source collection (under a prefix).

### Example

If a structure declaration contains the following statement

```php
class MyCollection extends Collection
{
    public function __construct(DatasourceContract $datasource)
    {
        parent::__construct(
            $datasource,
            'Movie'
        );

        // [...]

        $this->addField('director', new ManyToOneSchema(
            foreignKey: 'directorId',
            foreignKeyTarget: 'id',
            foreignCollection: 'People'
        ));
    }
}
```

Then the collection must accept references to fields from the `people` collection under the `director` prefix in all method parameters.

```php
use ForestAdmin\AgentPHP\DatasourceToolkit\Components\Caller;
use ForestAdmin\AgentPHP\DatasourceToolkit\Components\Query\ConditionTree\Nodes\ConditionTreeBranch;
use ForestAdmin\AgentPHP\DatasourceToolkit\Components\Query\ConditionTree\Nodes\ConditionTreeLeaf;
use ForestAdmin\AgentPHP\DatasourceToolkit\Components\Query\Filters\PaginatedFilter;
use ForestAdmin\AgentPHP\DatasourceToolkit\Components\Query\Sort;

$dataSource->getCollection('Movie')->list(
    $caller,
    new PaginatedFilter(
        conditionTree: new ConditionTreeBranch(
            aggregator: 'and',
            conditions: [
                new ConditionTreeLeaf(
                    field: 'title',
                    operator: 'Equal',
                    value: 'E.T.'
                ),
                new ConditionTreeLeaf(
                    field: 'director:firstName',
                    operator: 'Equal',
                    value: 'Steven'
                ),
            ],
        ),
        sort: new Sort(
            [
               [
                  'field'     => 'director:birthDate',
                  'ascending' => true,
               ],
            ]
        )
    )
);
```

should return

```json
{
  "id": 34,
  "title": "E.T",
  "director": { "firstName": "Steven", "lastName": "Spielberg" }
}
```