Question

I am trying the EF5 CodeFirst and cannot get the simple setup to work ;(

I have two classes Foo and Bar where Bar represent lookup table.

public class Foo
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual Bar Bar { get; set; }

}

public class Bar
{
    public int Id { get; set; }
    public string Description { get; set; }
}

public class MyDbContext : DbContext
{
    static MyDbContext()
    {
        Database.SetInitializer<MyDbContext>(null);
    }

    public MyDbContext(): base("testEF"){}

    public DbSet<Foo> Foos { get; set; }
    public DbSet<Bar> Bars { get; set; }
}

Now I have created a static class that serves as DataAccess Layer – in real-world application it will be on different physical tier

public static class DataAccess
{
    public static Bar GetBarById(int id)
    {
        using (var db = new MyDbContext())
        {
            return db.Bars.SingleOrDefault(b => b.Id == id);
        }
    }

    public static Foo InsertFoo(Foo foo)
    {
        using (var db = new MyDbContext())
        {
            db.Foos.Add(foo);

            db.SaveChanges();
        }
        return foo;
    }
}

I am initializing the DB with seed method:

internal sealed class Configuration : DbMigrationsConfiguration<testEF.MyDbContext>
{
    public Configuration()
    {
        AutomaticMigrationsEnabled = false;
    }
    protected override void Seed(testEF.MyDbContext context)
    {
            context.Bars.AddOrUpdate(
                new Bar { Description = "Bar_1" },
                new Bar { Description = "Bar_2" }

                );
    }
}

This creates two records in Bars table. So far so good…

Here is my Main function

static void Main(string[] args)
{
    var bar1 = DataAccess.GetBarById(1); 

    var foo = new Foo
    {
        Name = "Foo_1",
        Bar = bar1
    };

    DataAccess.InsertFoo(foo);

}

After the app runes there is a record in the Foos table:

Id       Name    Bar_Id
1        Foo_1   3   

Why Bar_Id is 3? The EF actually inserted new record to Bars table!

Id  Description
1   Bar_1
2   Bar_2
3   Bar_1

What I am doing wrong?

UPDATE:
I have found a workaround – to attach Bar property prior to inserting the record:

public static Foo InsertFoo(Foo foo)
{
    using (var db = new MyDbContext())
    {
        db.Bars.Attach(foo.Bar);

        db.Foos.Add(foo);

        db.SaveChanges();
    }
    return foo;
}

It is working now but this is more like a hack than a valid solution…
In real-world application the complexity of the objects could become a huge problem.
I am open to better solutions

Answer 1

The problem is that bar1 comes from a different data context. Your InsertFoo method implicitly adds it to the second context by building a relationship with the Foo. You want these two to share a context. So use a single context for the whole scope of the Main method.