Entity Framework Code First - Orphaning solutions? - entity-framework-4.1

Question

I have searched around for a good amount of time trying to find a satisfactory solution to the orphan issue common in EF.
One of the simplest forms of orphaning is the clearing of a collection of entities. The relationship between the entities is removed but the child entities still remain in the database.
My requirements: -
The clearing of the collection occurs in the domain and I want to simply be able to call clear and no more.
Any logic to figure out whether the relationship between the parent and child has been broken resulting in the delete needs to be encapsulated within the repository / DbContext.
I don't want to have to 'dirty' the domain with anything additional in order to solve this problem. This includes back references.
I suspect that this can't be solved as I have have spent considerable time looking for solutions but I ask out of hope!
Areas I have looked at are the ChangeTracker and any possible events which I can hook into, similar to AssociationChanged event which has popped up in various places. Something, somewhere in the DbContext must know that this relationship has been broken. How to access it, that is the question?
Thanks.

Answer 1

Can you try the following solution? Mb it fits your needs. The DeleteOrphans extension method must be called between DetectChanges and SaveChanges methods.
public static class DbContextExtensions
{
private static readonly ConcurrentDictionary< EntityType, ReadOnlyDictionary< string, NavigationProperty>> s_navPropMappings = new ConcurrentDictionary< EntityType, ReadOnlyDictionary< string, NavigationProperty>>();
public static void DeleteOrphans( this DbContext source )
{
var context = ((IObjectContextAdapter)source).ObjectContext;
foreach (var entry in context.ObjectStateManager.GetObjectStateEntries(EntityState.Modified))
{
var entityType = entry.EntitySet.ElementType as EntityType;
if (entityType == null)
continue;
var navPropMap = s_navPropMappings.GetOrAdd(entityType, CreateNavigationPropertyMap);
var props = entry.GetModifiedProperties().ToArray();
foreach (var prop in props)
{
NavigationProperty navProp;
if (!navPropMap.TryGetValue(prop, out navProp))
continue;
var related = entry.RelationshipManager.GetRelatedEnd(navProp.RelationshipType.FullName, navProp.ToEndMember.Name);
var enumerator = related.GetEnumerator();
if (enumerator.MoveNext() && enumerator.Current != null)
continue;
entry.Delete();
break;
}
}
}
private static ReadOnlyDictionary<string, NavigationProperty> CreateNavigationPropertyMap( EntityType type )
{
var result = type.NavigationProperties
.Where(v => v.FromEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many)
.Where(v => v.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.One || (v.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.ZeroOrOne && v.FromEndMember.GetEntityType() == v.ToEndMember.GetEntityType()))
.Select(v => new { NavigationProperty = v, DependentProperties = v.GetDependentProperties().Take(2).ToArray() })
.Where(v => v.DependentProperties.Length == 1)
.ToDictionary(v => v.DependentProperties[0].Name, v => v.NavigationProperty);
return new ReadOnlyDictionary<string, NavigationProperty>(result);
}
}