Conditional mapping with graphdiff

Question

I have following entities in my DbContext :

public class A
{
   public A()
   {
       Bs = new List<B>(); 
   }

   public ICollection<B> Bs { set; get; }
}   

Sometimes I Want to update a graph:

var a = dbContext.As
       .AsNoTracking()
       .Include(x=>x.Bs)
       .firstOrDefault();

var c = new C();
a.Bs.Add(c);

var d = new D();
var e1 = new E();
var e2 = new E();
d.Es.Add(e1); //<-- added new E
d.Es.Add(e2); //<-- added new E

a.Bs.Add(d);

I want to update a with its Bs (update C , D , E too) using graphdiff :

dbContext.UpdateGraph(a,map=>map.OwnedCollection(x=>x.Bs));

This updates A , B s, C s, D s, but not E s.

So I think, I need to define a conditional mapping for graphdiff , to update E s too, somethings like:

dbContext.UpdateGraph(a,map=>map.OwnedCollection(x=>x.Bs.OfType<D>(), 
                                             with =>with.OwnedCollection(t=>t.Es))
                                .OwnedCollection(x=>x.Bs.OfType<C>()));

Is there any way to do this job?

Answer 1

You can use this with graphdiff:

dbContext.UpdateGraph(a, map => map
    .OwnedCollection(b => p.Bs, with => with
    .AssociatedCollection(p => p.Es)));

see this link: GraphDiff Explanation

Answer 2

I don't believe that is possible using your current class structure. However, I found a way to accomplish this, but you have to make some changes in your code.

Update the A :

public class A
{
   public A()
   {
       Cs = new List<C>(); 
       Ds = new List<D>(); 
   }

   //PK
   public int AId { get; set; }

   public ICollection<C> Cs { set; get; }
   public ICollection<D> Ds { set; get; }       
} 

Update B , C , and D :

public class B
{
    public int BId { get; set; }
}

public class C : B
{
    //FK that links C to A
    public int FK_C_AId { get; set; }
}

public class D : B
{
    //FK that links D to A
    public int FK_D_AId { get; set; }

    public ICollection<E> Es { get; set; }

    public D()
    {
        Es = new List<E>();
    }
}

In order to maintain the TPH strategy, some mappings are necessary.

modelBuilder.Entity<A>()
    .HasMany(i => i.Cs)
    .WithRequired()
    .HasForeignKey(i => i.FK_C_AId)
    .WillCascadeOnDelete(false);

modelBuilder.Entity<A>()
    .HasMany(i => i.Ds)
    .WithRequired()
    .HasForeignKey(i => i.FK_D_AId)
    .WillCascadeOnDelete(false);

modelBuilder.Entity<B>()
    .Map<C>(m => m.Requires("Discriminator").HasValue("C"))
    .Map<D>(m => m.Requires("Discriminator").HasValue("D"));

Now, you have almost the same database structure. C and D are still mapped to the same table.

Finally, update the Graph:

context.UpdateGraph(a, map => map
    .OwnedCollection(b => b.Cs)
    .OwnedCollection(b => b.Ds, with => with
        .AssociatedCollection(e => e.Es)));

Hope it helps!