Question

I use Entity Framework with ASP.NET MVC3 Code First.

I have a project entity and logo like this:

public class Project
{
    [Key]
    public int      ProjectID   { get; set; }
    public string   Name        { get; set; }
    public string   Description { get; set; }        

    public virtual  Logo Logo   { get; set; }
}

public class Logo
{
    [Key]
    public int    LogoID          { get; set; }
    public string LogoName        { get; set; }
    public byte[] LogoContent     { get; set; }
    public string LogoContentType { get; set; }
}

Each project can have 0 or 1 logo attached.

When my database (sql server) is created, I see that a field is created in the table Project for referencing the logo.

Whenever I have a project in my Project table referencing a logo,I have the Logo_LogoID filled with the corresponding key in the logo table. That’s ok for me. What seems strange to me is when I delete the logo, sql server show me the error below:

So in order to be able to delete a logo from my Logo table, I need first to break the reference from the Project table (by replacing the LogoID with NULL) and next delete the row from Logo.

Maybe there is a better way of referencing things?

This may seems a stupid question.

I think a better solution would be to have the inverse relation: the ProjectID field added in the Logo table. So whenever I need to delete a logo, I can easily delete the Logo.

What do you think?

Thanks.

EDIT

Like Mark Oreta suggest, I tried with:

        modelBuilder.Entity<Project>()
            .HasOptional(p => p.Logo)
            .WithOptionalPrincipal(); 

But I got a double reference to ProjectID:

Any idea why?

Answer 1

You can change the mapping by overwriting your OnModelCreating in your DbContext with this:

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Project>()
            .HasOptional(p => p.Logo)
            .WithOptionalPrincipal();
    }

This will create a Project_ProjectID on your Logo entity.

If you want to customize the name – you said you were ok with it, but you might want to change it later, you can add this to the end:

.Map(m => m.MapKey("ProjectId")

and it will map to ProjectId on your Logo entity.