Azure Mobile App - error with Entity Framework attempting to re-Insert child - when using $expand

Question

I am looking at Azure Mobile App and have setup a test service and client.

I've setup the following Entities service-side:

public class Hotel : EntityData
{
    public string Title { get; set; }

    public virtual ICollection<Booking> Bookings { get; set; }
}

public class Booking : EntityData
{
    public BookingStatus BookingStatus { get; set; }

    [ForeignKey("PersonId")]
    public virtual Person Person { get; set; }

    [ForeignKey("HotelId")]
    public virtual Hotel Hotel { get; set; }

    public string PersonId { get; set; }

    public string HotelId { get; set; }
}

public class Person : EntityData
{
    public string Name { get; set; }

    public virtual ICollection<Booking> Bookings { get; set; }
}

And the controller:

public class BookingController : TableController<Booking>
{
    protected override void Initialize(HttpControllerContext controllerContext)
    {
        base.Initialize(controllerContext);
        MobileServiceContext context = new MobileServiceContext();
        DomainManager = new EntityDomainManager<Booking>(context, Request);
    }

    // GET tables/Booking/48D68C86-6EA6-4C25-AA33-223FC9A27959
    public SingleResult<Booking> GetBooking(string id)
    {
        return Lookup(id);
    }

    // GET tables/Booking
    public IQueryable<Booking> GetAllBookings()
    {
        return Query();
    }

    // PATCH tables/Booking/48D68C86-6EA6-4C25-AA33-223FC9A27959
    public Task<Booking> PatchBooking(string id, Delta<Booking> patch)
    {
        return UpdateAsync(id, patch);
    }
}

I have added some default data using CreateDatabaseIfNotExists<MobileServiceContext> and when I startup and test the Web API, the DB gets populated and I am happy that the Keys/Relationships are setup correctly. I am just using the Code First convention naming (as per this tutorial)

I have also created a test client with the following Entities:

public class Person
{
    public string Id { get; set; }
    public byte[] Version { get; set; }

    public string Name { get; set; }
    public virtual ICollection<Booking> Bookings { get; set; }
}

public class Booking
{
    public string Id { get; set; }
    public byte[] Version { get; set; }

    public BookingStatus BookingStatus { get; set; }
    public string PersonId { get; set; }
    public string HotelId { get; set; }        
    public virtual Person Person { get; set; }
    public virtual Hotel Hotel { get; set; }
}

public class Hotel
{
    public string Id { get; set; }
    public byte[] Version { get; set; }

    public string Title { get; set; }
    public virtual ICollection<Booking> Bookings { get; set; }
}

And with this test logic:

using (var client = new MobileServiceClient(m_Url, new ODataParameterHandler())
{
    client.SerializerSettings.PreserveReferencesHandling = PreserveReferencesHandling.Objects;
    client.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;

    var bookingTable = client.GetTable<Booking>();
    var bookings = await placementTable
                .Where(p => p.BookingStatus == BookingStatus.Confirmed && p.PersonId == 10)
                .WithParameters(new Dictionary<string, string> { { "expand", "Hotel" } })
                .ToListAsync();

    var aBooking = bookings[0];     
    aBooking.BookingStatus = BookingStatus.Cancelled;

    await bookingTable.UpdateAsync(aBooking);
}

// Class to allow $expand= querystring value to be passed in.
public class ODataParameterHandler : DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        UriBuilder builder = new UriBuilder(request.RequestUri);

        builder.Query = builder.Query
            .Replace("expand", "$expand")
            .TrimStart('?');

        request.RequestUri = builder.Uri;

        return await base.SendAsync(request, cancellationToken);
    }
}

The GET/ToListAsync works ok and I get the child Hotel object attached to my Booking. However, the Update fails with:

The operation failed due to a conflict: 'Violation of PRIMARY KEY constraint 'PK_dbo.Hotels'. Cannot insert duplicate key in object 'dbo.Hotels'. The duplicate key value is (0e6e1bae-bd59-46ac-9630-a2b53dd04a90).\r\nThe statement has been terminated.

But why on earth is it attemping to INSERT my child object again? Firstly, I haven't altered it, and secondly, it has an Id, CreatedAt etc.

I cannot find any similar issues regarding Azure Mobile Apps, but I did find this SO Post regarding Entity Framework but the OP talks about having manually created the children, so I am not sure it fully applies as I have fetched the child Entity from the DB through the TableController.

Answer 1

Azure Mobile Apps does not support relationships. You are bumping into one of the many issues that go along with that.

If you are using offline sync, then decompose the tables so that the linkage is less required, then sync each table individually.

If you are not using offline sync, use a custom API to commit the change to the database.