> ## Documentation Index
> Fetch the complete documentation index at: https://easyaf.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# EntitySet Filters

> Control query results by filtering EntitySets based on business rules

# EntitySet Filters

Have you ever wanted to limit the results of a particular query based on the current user, or maybe you only want to return results that are marked "active"?

<Info>
  EntitySet Filters allow you to consistently control the shape of the results returned from particular EntitySets, even across navigation properties.
</Info>

## Convention-Based Filtering

Like the rest of RESTier, this is accomplished through a simple convention that meets the following criteria:

<Steps>
  <Step title="Method naming convention">
    The filter method name must be `OnFilter{EntitySetName}`, where `{EntitySetName}` is the name of the target EntitySet.
  </Step>

  <Step title="Method visibility">
    It must be a `protected internal` method on the implementing `EntityFrameworkApi` class.
  </Step>

  <Step title="Method signature">
    It should accept an `IQueryable<T>` parameter and return an `IQueryable<T>` result where `T` is the Entity type.
  </Step>
</Steps>

### Example

<CodeGroup>
  ```csharp OnFilterPeople - Filter to users with trips theme={"dark"}
  ///<summary>
  /// Filters queries to the People EntitySet to only return Users that have Trips.
  ///</summary>
  protected internal IQueryable<Person> OnFilterPeople(IQueryable<Person> entitySet)
  {
      return entitySet.Where(c => c.Trips.Any()).AsQueryable();
  }
  ```

  ```csharp OnFilterTrips - Filter to current user theme={"dark"}
  ///<summary>
  /// Filters queries to the Trips EntitySet to only return the current user's Trips.
  ///</summary>
  protected internal IQueryable<Trip> OnFilterTrips(IQueryable<Trip> entitySet)
  {
      return entitySet.Where(c => c.PersonId == ClaimsPrincipal.Current.FindFirst("currentUserId")).AsQueryable();
  }
  ```

  ```csharp TrippinApi.cs - Full example theme={"dark"}
  using Microsoft.Restier.Core;
  using Microsoft.Restier.Provider.EntityFramework;
  using System.Data.Entity;
  using System.Linq;
  using System.Security.Claims;
  using System.Threading.Tasks;

  namespace Microsoft.OData.Service.Sample.Trippin.Api
  {
      ///<summary>
      /// Customizations to the EntityFrameworkApi for the TripPin service.
      ///</summary>
      ///<example>
      /// Add the following line in WebApiConfig.cs to register this code:
      /// await config.MapRestierRoute<TrippinApi>("Trippin", "api", new RestierBatchHandler(GlobalConfiguration.DefaultServer));
      ///</example>
      public class TrippinApi : EntityFrameworkApi<TrippinModel>
      {
          ///<summary>
          /// Filters queries to the People EntitySet to only return Users that have Trips.
          ///</summary>
          protected internal IQueryable<Person> OnFilterPeople(IQueryable<Person> entitySet)
          {
              return entitySet.Where(c => c.Trips.Any()).AsQueryable();
          }

          ///<summary>
          /// Filters queries to the Trips EntitySet to only return the current user's Trips.
          ///</summary>
          protected internal IQueryable<Trip> OnFilterTrips(IQueryable<Trip> entitySet)
          {
              return entitySet.Where(c => c.PersonId == ClaimsPrincipal.Current.FindFirst("currentUserId")).AsQueryable();
          }
      }
  }
  ```
</CodeGroup>

## Centralized Filtering

<Warning>
  TODO: Pull content from Section 2.8.
</Warning>