InvalidOperationException saving entity

I am currently using Beta 8

User model

public class User 
{
     public string Id { get; set; }
     public string Email { get; set; }
}

Saving the entity

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

When i try to save the entity i get the following exception, and i am not sure why and what this means. The entity is created in the DB, so it seems to be working, but EF throws this exception. Not sure if this is a bug, or just me doing something wrong.

An unhandled exception occurred while processing the request. InvalidOperationException: The >property ‘Id’ on entity type ‘User’ has a temporary value while attempting to change the entity’s >state to ‘Unchanged’. Either set a permanent value explicitly or ensure that the database is >configured to generate values for this property.

[rowanmiller]

Hey,

Sounds like you are probably trying to save a User without assigning a primary key value. In the following code the first SaveChanges succeeds, but the second one throws the exception you are seeing.

using Microsoft.Data.Entity;

namespace ConsoleApplication10
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var db  = new UserContext())
            {
                db.Database.EnsureCreated();

                db.Users.Add(new User { Id = "user1", Email = "[e-mail]" });
                db.SaveChanges();

                db.Users.Add(new User { Email = "[e-mail]" });
                db.SaveChanges();
            }
        }
    }

    public class User
    {
        public string Id { get; set; }
        public string Email { get; set; }
    }

    public class UserContext : DbContext
    {
        public DbSet<User> Users { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=Demo;Trusted_Connection=True;");
        }
    }
}

In RC1 we have made some changes in this area to try and make things a little clearer. Instead of that exception during SaveChanges you now get this when you try to add the entity.

System.InvalidOperationException: The instance of entity type ‘ConsoleApplication10.User’ cannot be tracked because it has an invalid (e.g. null or CLR default) primary key. Either set the key explicitly or consider using an IValueGenerator to generate unique key values.

[ajcvickers]

@ppumkin DbContext is not thread-safe. That is, the same instance cannot be used by multiple threads concurrently. Tasks.WaitAll is causing that to happen, so it can’t be used for this kind of thing.