OData Model Configurations

A model configuration enables OData service authors to apply model setups that are specific to a service API version. The VersionedODataModelBuilder will call Apply for each discovered API version with the current ODataModelBuilder.

public interface IModelConfiguration
{
   void Apply( ODataModelBuilder builder, ApiVersion apiVersion, string routePrefix );
}

The implementation of a model configuration can provide all variations of a model or they can be spit across multiple implementations. The applied model does not have to be same across API versions.

Consider the following model:

public class Person
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public string Phone { get; set; }
}

Let us assume that the OData service for this model has three versions: "1.0", "2.0", and "3.0". In API version "1.0", a person had the properties "Id", "FirstName", and "LastName". In API version "2.0" we introduced the "Email" property. In API version "3.0" we introduced the "Phone" property. If we implement the entire model configuration in a single class, it might look like:

public class PersonModelConfiguration : IModelConfiguration
{
    private void ConfigureV1( ODataModelBuilder builder ) =>
        ConfigureCurrent( builder ).Ignore( p => p.Email ).Ignore( p => p.Phone );

    private void ConfigureV2( ODataModelBuilder builder ) =>
        ConfigureCurrent( builder ).Ignore( p => p.Phone );

    private EntityTypeConfiguration<Person> ConfigureCurrent( ODataModelBuilder builder )
    {
        var person = builder.EntitySet<Person>( "People" ).EntityType;
        person.HasKey( p => p.Id );
        return person;
    }

    public void Apply( ODataModelBuilder builder, ApiVersion apiVersion, string routePrefix )
    {
        switch ( apiVersion.MajorVersion )
        {
            case 1:
                ConfigureV1( builder );
                break;
            case 2:
                ConfigureV2( builder );
                break;
            default:
                ConfigureCurrent( builder );
                break;
        }
    }
}

Even through we have a single Person object, the EDM associated with the service API version will render the model according the requested API version.

~/people(1)?api-version=1.0

{
   "id": 1,
   "firstName": "John",
   "lastName": "Doe"
}

~/people(1)?api-version=2.0

{
   "id": 1,
   "firstName": "John",
   "lastName": "Doe",
   "email": "john.doe@somewhere.com"
}

~/people(1)?api-version=3.0

{
   "id": 1,
   "firstName": "John",
   "lastName": "Doe",
   "email": "john.doe@somewhere.com",
   "phone": "555-555-5555"
}

ASP.NET Core and OData

Dependency Injection is a first-class concept in ASP.NET Core. This intrinsic capability enables API versioning to automatically register all discovered implementations of IModelConfiguration. API versioning also registers a single, but replaceable mapping for VersionedODataModelBuilder. This enables you to declare VersionedODataModelBuilder as a dependent parameter wherever you would like ASP.NET Core to inject the configured instance. The injected instance will always have all of the discovered IModelConfiguration instances, but you can continue to modify the builder until you are ready to create all of the EDMs via VersionedODataModelBuilder.GetEdmModels().