.Net Entity Framework Updating Objects in N-Tier Environment

Oh, Boy. OK, Phew. This was quite the deal to get Objects with navigation properties to update. The issue with updates is this, when using the method:

yourcontext.ApplyPropertyChanges(key.EntitySetName, o);

It only works on scalar properties in your entity object. Not the navigation properties or the reference objects (Foreign Key Relationships). I composed from the very few resources on the entity framework this method in my WCF Service:
Credits to this blog entry for guiding me in the right direction. Check it out.

private void Update(System.Data.Objects.DataClasses.EntityObject o)
    {
        EntityKey key;
        Object originalItem;

        using (CorporateEntities ce = new CorporateEntities())
        {
            key = ce.CreateEntityKey(o.EntityKey.EntitySetName, o);

            if (ce.TryGetObjectByKey(key, out originalItem))
            {
                ce.ApplyPropertyChanges(
                        key.EntitySetName, o);

                foreach (var entityrelationship in ((IEntityWithRelationships)originalItem).RelationshipManager.GetAllRelatedEnds())
                {
                    var oldRef = entityrelationship as EntityReference;

                    if (oldRef != null)
                    {
                        var newRef = ((IEntityWithRelationships)o).RelationshipManager.GetRelatedEnd(oldRef.RelationshipName, oldRef.TargetRoleName) as EntityReference;
                        oldRef.EntityKey = newRef.EntityKey;
                    }
                }
            }

            ce.SaveChanges();
        }
    }

This method takes the new object and updates the old objects EntityKeys. Why do we have to cast the Entity Object to IEntityWithRelationShips? According to documentation on MSDN it implements IEntityWithRelationShips. Check it out Shouldn’t it be available already. Anyway, Once we do this we can retrieve each navigation property or references; then change the old to the new. However, there is a catch here. If You do not change the entity key on the YourObjectReference it will not update it with new reference object. For example on the client:

Stores updateStore = client.GetStoreByID(666);
/*This has no effect as the updateStore.ConceptsReference will not be updated by the line below*/
updateStore.Concepts = client.GetConcept(3);

“Concepts” is the navigation property and seems logical to assign new object to this, but unfortunately it will have no effect on updating because the updateStore.ConceptReference still points to the original entity. So we need to change the reference. In my WCF Service I have created the following method to do this for me. The not so cool part is that I pass in the navigation properties or objects as a separate parameter on the method. This is to abstract the Presentation Layer from having Entity Framework (EF) specific code in it. Remember ideally the presentation layer should only worry about business objects, not specific Data Access Layer (DAL) nuances.

public void UpDateStore(Stores updatedStore, Concepts concept, StoreStatus status, Distributors distributors, POSSystems pos)
    {
        EntityReference c = new EntityReference();
        c.EntityKey = concept.EntityKey;
        updatedStore.ConceptsReference = c;

        EntityReference s = new EntityReference();
        s.EntityKey = status.EntityKey;
        updatedStore.StoreStatusReference = s;

        EntityReference d = new EntityReference();
        d.EntityKey = distributors.EntityKey;
        updatedStore.DistributorsReference = d;

        EntityReference p = new EntityReference();
        p.EntityKey = pos.EntityKey;
        updatedStore.POSSystemsReference = p;

        updatedStore.ModifiedDate = DateTime.Now;
        this.Update(updatedStore);
    }

So now when I call my private update method in the WCF Service it will indeed update!

Client code:

Stores updateStore = client.GetStoreByID(666);
client.UpDateStore(updateStore, client.GetConcept(2), client.GetStat(2), client.GetDistributor(2), client.GetPOSSystem(2));

Hope this helps anyone else struggling with this situation. Better yet if someone can post a more elegant solution that would be great. There is very little information on real world examples of using Entity Framework, especially in N-Tier environment.

Note and Disclaimer: This is test code and may contain bugs and/or improper error handling, it is for academic purposes only, for sharing knowledge, and collaboratively coming up with better solutions. Please always practice proper security, error handling, and coding best practices in production. I am not liable for any code used here; use @ your own risk. Have fun and share the experience and knowledge. Remember, no question is a stupid question, and failure gives us insight.