WCF RIA Services Compositions with Entity Framework
I haven't been working on anything outside Genexus, Deklarit and Genexus Server for a while, so when my friend Mateo asked to help him on a new project for a client of his, based on brand new Microsoft technologies, I was saying yes before the end of the sentence.
This blog post and probably some more to come will be related to our experience with Entity Framework 4, RIA Services 1 and Silverlight 4.
But in this particular case I wanted to blog about a problem we had with Compositions. Compositions are very useful when you have an Association where a Parent entity needs to have its children all the time.
The Update method of parent entities is a bit different than regular entities. I took the patter from this article (Compositional Hierarchies) but things didn’t work as expected. I have to add that “m generating POCO entities and using the Unit Of Work pattern so it wasn’t easy just copy and paste the code for the article. I posted a few questions to the RIA services forum and found out that that pattern exposed a bug :(
Fortunately I was redirected this post from Brett Samblament which described the new pattern to follow to write a fully functional UpdateParent method. But again, I can’t just copy and paste, so here’s the code I wrote for it. Also, by using generic, I’m able to call the exact pattern for every composition in my model, cool uh?!
public void UpdateParent(Parent parent)
{
EntityHelper.UpdateParentEntity(parent, ObjectContext.Parents, ChangeSet, ObjectContext);
foreach (Child child in ChangeSet.GetAssociatedChanges(parent, o => o.Children))
EntityHelper.UpdateChildEntity(child, ObjectContext.Children, ChangeSet, ObjectContext);
}
And my EntityHelper class has the following methods:
public static void UpdateParentEntity<T>(T entity, IRepository<T> repository, ChangeSet chgSet, IUnitOfWork oc)
where T : class
{
try
{
ObjectContext ctx = oc as ObjectContext;
repository.ObjectSet.AddObject(entity);
T originalEntity = chgSet.GetOriginal<T>(entity);
if (originalEntity == null)
ctx.ObjectStateManager.ChangeObjectState(entity, EntityState.Unchanged);
else
repository.ObjectSet.AttachAsModified(entity, originalEntity);
}
catch (Exception ex)
{
TraceManager.Error(string.Format("An error occurred updating a {0}", typeof(T)), ex);
throw;
}
}
public static void UpdateChildEntity<T>(T entity, IRepository<T> repository, ChangeSet chgSet, IUnitOfWork oc)
where T : class
{
try
{
ObjectContext ctx = oc as ObjectContext;
ChangeOperation change = chgSet.GetChangeOperation(entity);
switch (change)
{
case ChangeOperation.Delete:
if (GetEntityState(entity, ctx) == EntityState.Detached)
repository.ObjectSet.Attach(entity);
ctx.DeleteObject(entity);
break;
case ChangeOperation.Insert:
// do nothing
break;
case ChangeOperation.None:
ctx.ObjectStateManager.ChangeObjectState(entity, EntityState.Unchanged);
break;
case ChangeOperation.Update:
T original = chgSet.GetOriginal<T>(entity);
if (original == null) { throw new Exception("Update with no original value found"); }
if (GetEntityState(entity, ctx) == EntityState.Detached)
repository.ObjectSet.Attach(entity);
repository.ObjectSet.AttachAsModified(entity, original);
break;
default:
break;
}
}
catch (Exception ex)
{
TraceManager.Error(string.Format("An error occurred updating a {0}", typeof(T)), ex);
throw;
}
}
public static EntityState GetEntityState(object entity, ObjectContext ctx)
{
System.Data.Objects.ObjectStateEntry ose;
if (ctx.ObjectStateManager.TryGetObjectStateEntry(entity, out ose))
return ose.State;
else
return EntityState.Detached;
}
I hope this helps someone clear the way… and I promise I’ll post more (and more often) about this.
As usual, this code is ‘works on my machine’ certified.
I never get tired of this
![works-on-my-machine-starburst_3_thumb[1]](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhw9-ej4g_575HRJAXgQvxdILF1jmHbpOVxoNne9b6VDRjuZzoDRzPaTAC2rG4pdLOG44NPRk6i5bJCH0FQ3QwnFqLk7zRgYnDOYVjznT_VDt1cGbvBA1emTBaRxkyPRybdGpTWww/s1600-h/works-on-my-machine-starburst_3_thumb%5B1%5D%5B3%5D.png "works-on-my-machine-starburst_3_thumb[1]")
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