Question

My question can better be explained via example code. I am using POCO with change tracking proxies that is generated by the C# POCO generator by default. Please see below.

Assume you have Movie, MusicDirector and Director in the database and the relationship between them is a Director & MusicDirector can direct multiple movies and a movie can have only one Director and MusicDirector. Since I am a new user and cannot post images, here is my db structure.

Movie table has MovieId, Name,MusicDirectorId,DirectorId

Director table has DirectorId, Name

MusicDirector table has MusicDirectorId, Name

Here is the link to the diagram. https://i.stack.imgur.com/ce49r.png.

I am trying to insert a new movie and the director and musicdirector “already exists” in the db. Below is my code.

Movie movie = new Movie();            
        movie.Name = "Movie1";
        movie.Director = new Director() { Name = "DirectorA" };           
        movie.MusicDirector = new MusicDirector() { Name = "MusicDirectorA" };

        using (TestEFEntities ctx = new TestEFEntities())
        {
            movie.Director = ctx.Directors.Where(x => x.Name == movie.Director.Name).FirstOrDefault();
            movie.MusicDirector = ctx.MusicDirectors.Where(x => x.Name == movie.MusicDirector.Name).FirstOrDefault();                                    
            ctx.Movies.AddObject(movie);                    
            ctx.SaveChanges();
        }

Now when I do this, MusicDirector record is added again even though it is overwritten by the record from the db. You may think why I am keeping this line movie.Director = new Director() { Name = “DirectorA” }; initially, it is an Asp.net MVC app where Movie object is bound with the director and musicdirector names the user adds. So, the first 4 lines are done implicitly by MVC and think all the other lines are in the service layer. Am I missing something as this is a very basic scenario and the framework should handle it? Of course, one solution to correct this problem is to create a new Movie object and assign the records from db which I don’t want to do as I have to copy all the properties from the movie object sent by controller. How can I solve this problem?

Also this works correctly in Self-Tracking Entities. Is this some kind of a limitation to POCO and it would be great if someone can explain the behavior?

Answer 1

If you are using POCOs, then your code should work as the way you expected. Alternatively, you can try to populated the FKs instead of assigning the whole object like this:

using (TestEFEntities ctx = new TestEFEntities())
{
    movie.DirectorID = ctx.Directors
        .Where(x => x.Name == movie.Director.Name).First().DirectorID;

    movie.MusicDirectorID = ctx.MusicDirectors
        .Where(x => x.Name == movie.MusicDirector.Name).First().MusicDirectorID;

    ctx.Movies.AddObject(movie);                    
    ctx.SaveChanges();
}