EF: Create/Remove relation from Many-to-Many relations when `AutoDetectChangesEnabled` and `ProxyCreationEnabled` are disabled on DbContext

Question

1. Knowning Foo.Id and Bar.Id how can I create their relation without loading the entities from the DB.

   class Foo {
       public in         
   
   
           

Answer 1

Ok, have found the solution and here is the helper method:

static void ChangeRelationship(
    IObjectContextAdapter ctx, 
    T1 a, 
    T2 b, 
    Expression> getNavigationProperty,
    EntityState state) where T1: class
{
    ctx
        .ObjectContext
        .ObjectStateManager
        .ChangeRelationshipState(
            a,
            b,
            getNavigationProperty,
            state
        );
}

And using it in my example from the question:

using (var ctx = new DbCtx())
{
    ctx.Configuration.LazyLoadingEnabled = false;
    ctx.Configuration.ProxyCreationEnabled = false;
    ctx.Configuration.AutoDetectChangesEnabled = false;
    ctx.Database.Log += Console.WriteLine;

    var foo = new Foo {Id = 1, Bars = new List()};
    var bar = new Bar { Id = 3, Foos = new List() };

    ctx.Entry(foo).State = EntityState.Unchanged;
    ctx.Entry(bar).State = EntityState.Unchanged;

    // create
    ChangeRelationship(ctx, foo, bar, x => x.Bars, EntityState.Added);
    ctx.SaveChanges();

    // remove
    ChangeRelationship(ctx, foo, bar, x => x.Bars, EntityState.Deleted);
    ctx.SaveChanges();
}