Microsoft.AspNet.OData.Extensions.ODataQueryMapper

A query mapper for OData v4.0, Automapper style. This extension allows you to have a different domain model than your database model, and still be able to pass the OData query down to the database.

Basic Usage

The following example uses the Album table from the Chinook database.

Initialize the mapper in your Startup.cs file:

ODataQueryMapper.Initialize(
    x =>
        {
            x.CreateMap<DomainAlbum, Album>("album")
                .ForMember(y => y.Id, y => y.AlbumId);
        });

(The CreateMap function creates the necessary code for your ODataController to work)

Next, create a controller that gets and transforms our data:

[ODataRoutePrefix("album")] // NOTE: This must be the same as the one registered in the initializer
public class AlbumODataController : ODataController
{
    private readonly IODataQueryMapper queryMapper;

    private readonly IMappingEngine mapper;

    public AlbumODataController(IODataQueryMapper queryMapper, IMappingEngine mapper)
    {
        this.queryMapper = queryMapper;
        this.mapper = mapper;
    }

    [ODataRoute]
    public async Task<IHttpActionResult> Get(ODataQueryOptions<DomainAlbum> query)
    {
        var mappedQuery = await this.queryMapper.Map<DomainAlbum, Album>(query);

        using (var context = new MyDatabaseContext()) // Using EF here, but other frameworks can be used
        {
            var dbTesult = mappedQuery.ApplyTo(context.Album.Include(x => x.Artist))

            // The database entities must be mapped back to your domain models, this example uses Automapper
            var result = this.mapper.Map<IEnumerable<DomainAlbum>>(dbResult);

            if (result != null && result.Any())
            {
                return this.Ok(result);
            }
        }

        return this.StatusCode(HttpStatusCode.NoContent);
    }
}

Advanced Usage

The ForMember method also accepts strings:

x.CreateMap<DomainAlbum, Album>("album")
    .ForMember("Artist/Value", y => y.ArtistId);
x.CreateMap<DomainAlbum, Album>("album")
    .ForMember("Artist/Value", "ArtistId");

Profiles

It is possible to create mapping profiles as separate classes, letting you better have control over your code:

x.AddProfile<MyProfile>();

public class MyProfile : IMappingProfile
{
    public void Configure(IProfileConfiguration configuration)
    {
        configuration.CreateMap<DomainArtist, Artist>("artist").ConvertUsing<ArtistConverter>();
    }
}

TypeConverters

It is also possible to create mapping tables as separate classes, letting you better have control over your code:

x.CreateMap<DomainArtist, Artist>("artist").ConvertUsing<MyConverter>();

public class MyConverter : ITypeConverter<DomainArtist, Artist>
{
    public Dictionary<string, string> CreateMappingTable()
    {
        return new Dictionary<string, string>()
                   {
                       { "Id", "ArtistId" }
                   };
    }
}

Important Notes

EnableQueryAttribute

You cannot use the [EnableQuery] attribute, as that will process your query twice, once in the ApplyTo call, and once when the request is leaving the server. Use the included [ValidateQuery] attribute instead. It takes care of validating the query according to your supplied settings, and does not process the result after ApplyTo has been called.

Nested properties

If you want to perform filtering on a nested property on your domain model, like Artist.Id, you need to use the string version of ForMember like this:

x.CreateMap<DomainAlbum, Album>("album")
    .ForMember("Artist/Id", "ArtistId");