EF Core 2.0 - Circular Dependency with required FK on either end

Question

I have a fairly simple data model consisting of two entities:

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int CurrentLocationId { get; set; }

    public List<Location> Locations { get; set; }
    public Location CurrentLocation { get; set; }
}

and

public class Location
{
    public int Id { get; set; }
    [Required]
    public int UserId { get; set; }
    public string Address { get; set; }

    public User User { get; set; }
}

then in order to get a successful migration to run I needed the following model builder code:

builder.Entity<Location>()
       .HasOne(x => x.User)
       .WithMany(x => x.Locations)
       .HasForeignKey(x => x.UserId);

This has generated a database as I'd expect and how I need it to be. However, I'm unable to save entities due to the following circular dependency error:

InvalidOperationException: Unable to save changes because a circular dependency was detected in the data to be saved: 'ForeignKey: User {'CurrentLocationId'} -> Location {'Id'} ToPrincipal: CurrentLocation, ForeignKey: Location {'UserId'} -> User {'Id'} ToDependent: Locations ToPrincipal: User'.

Is there a way around this in EF Core 2.0?

I have a few options to circumnavigate it by changing my data model, but this is the preferred approach as I can use DB constraints to ensure that all Locations link back to a User, and that every user must have a CurrentLocation set. I know it would solve the issue but I can't really allow nulls on the CurrentLocation field!

The code I'm using to try and store users is as follows (simplified for demo purposes):

var location = new Location
{
    Address = "Some address"
};

_context.Locations.Add(location);

var user = new User
{
    Name = "Stu"
};

_context.Users.Add(user);

user.Locations = new List<Location>
{
    location
};

user.CurrentLocation = location;

await _context.SaveChangesAsync();

and I've also tried

var location = new Location
{
    Address = "Some address"
};

var user = new User
{
    Name = "Stu",
    Locations = new List<Location>
    {
        location
    },
    CurrentLocation = location
};

_context.Users.Add(user);    
await _context.SaveChangesAsync();

But the error remains the same. Can this be fixed by some kind of fancy ModelBuilder overrides? Or am I restricted to changing my data model / allowing nulls where I shouldn't really be allowing nulls?

Thanks in advance!

So... how did you solve this? – Konrad May 03 '18 at 17:16 — Konrad, May 03 '18 at 17:16

score 2 · Answer 1 · answered Nov 15 '17 at 15:05

2

To answer my own question - just checked and SQL server doesn't support deferrable constraints, so nothing EF can do anyway! Change to the data model it is.

answered Nov 15 '17 at 15:05

Stu Ratcliffe

269
3
14

1

Minimally make User.CurrentLocationId nullable so you can insert a user without a Location to break the cycle. – David Browne - Microsoft Nov 15 '17 at 15:09

EF Core 2.0 - Circular Dependency with required FK on either end

1 Answers1