实体框架再次插入现有的引用实体

Question

I'm not really what is wrong with my code.

I try to use an existing entity (Location) and use it as one of the properties of another entity (ApplicationUser) .

I expect the ApplicationUser to reference the existing Location but it, instead, creates a new Location and reference this instead.

Here are the entities:

public class ApplicationUser : IdentityUser
{
    public int? LocationId { get; set; }
    public Location Location { get; set; } 
}


public class Location
{
    public Location()
    {
        this.Users = new HashSet<ApplicationUser>();
    }

    public int LocationId { get; set; }
    public string Country { get; set; }
    public string Province { get; set; }
    public string Area { get; set; }

    public virtual ICollection<ApplicationUser> Users { get; set; }
}

Here are my configurations:

public class ApplicationUserConfiguration : EntityTypeConfiguration<ApplicationUser>
{
    public ApplicationUserConfiguration()
    {
        this.HasOptional(i => i.Location)
            .WithMany(i => i.Users)
            .HasForeignKey(i => i.LocationId);
    }
}

public class LocationConfiguration : EntityTypeConfiguration<Location>
{
    public LocationConfiguration()
    {
        this.HasKey(i => i.LocationId);
        this.Property(i => i.Country).HasMaxLength(100);
        this.Property(i => i.Province).HasMaxLength(100);
        this.Property(i => i.Area).HasMaxLength(100);
    }
}

Here is how I save locations:

public Task SaveAsync(IUnitOfWork unitOfWork, Location entity)
{
        var context = (ApplicationDbContext)unitOfWork.Context;
        context.Entry(entity).State = entity.LocationId == 0
           ? EntityState.Added
           : EntityState.Modified;
        return context.SaveChangesAsync();
}

On my code, I pre-populate first the locations. And then I call an existing location to be used as the location of a user.

//successfully called an existing location. LocationId is 5
var adminLocation = await this._locationService.FindByArea("Philippines", "Laguna", "Calamba");

admin = new ApplicationUser
            {
               LockoutEnabled = false,
               Email = Settings.Default.DefaultAdminEmail,
               UserName = Settings.Default.DefaultAdminUserName,
               FirstName = "admin",
               LastName = "yow",

               // used here
               Location = adminLocation
             };

// save user
var identityResult = await this._userService.RegisterUserAsync(admin, 
    Settings.Default.DefaultAdminPassword);

After execution, upon checking the database, I get images below.

I'm still wondering why it saved a new Location. When I debug my application, it does not call the Location save method when creating the user.

Is there anything wrong with my configuration perhaps? Thanks guys.

Location Table:

User Table using the wrong Location:

Answer 1

It's giving you duplicates because you're setting the wrong field. You should be setting the LocationID itself with the ID of the Location record you want to use, not the navigational property. EF does this because it pays more attention to the ID, rather than the ID on the navigational property. When it sees a Location record present on the object, but sees that the LocationID is 0 it assumes that the user is intending to create a brand new Location , and will thus put a new one into the database.

It sounds ridiculous, I know, but that's EF for you.

I wrote a blog post about that with more information on this same issue here .