Combining individual Entity Framework objects

I have a scenario where I am using Entity Framework in a WCF service and the changes are happening on an untracked instance of a type that maps to the database by code (non-trivial updates and deletions in all the instance object tree). When I try to hook up an untracked instance in context, EF only recognizes changes to simple value types in the root object.

Does anyone know of an elegant solution for this scenario? I'm looking for a way to do this by using a shared repository and avoiding having to run through the entire object tree managing the "attach / detach" state of each object. I suggested that it might be possible to use ValueInjecter or AutoMapper to trigger changes on a fully moistened and tracked "old" state instance so that the context can carry over the changes. Also, how does Nhibernate handle this situation?

Thanks in advance for logging in!

UPDATE (7/31/2012): I've updated the code to handle typed keys and some typing issues with EF Proxies. Also added some helper extensions when working with IEntity types. This implementation is not perfect, but it is very functional.

UPDATE (3/13/2012): I added a feature request for cleaner merge in EF. The request is here: http://data.uservoice.com/forums/72025-ado-net-entity-framework-ef-feature-suggestions/suggestions/2679160-better-merging-change-tracking

UPDATE (3/12/2012): I posted my solution below. It uses FubuCore , ValueInjecter , and requires objects to be tagged with one of two interfaces , either IEntity or IRecursiveEntity for recursive classes. The solution will handle recursive, self-linked objects.

Also, I link to a shared repository (repository) that allows me to get a link to the IDbSet that EF provides. This can be complemented by any other general or specific repository. Finally, does IEntity interface use int? id, however you can define what you want (Guid / Guid?). The solution itself is not as elegant as we would like, however it allows for much more elegant data access code when outside the physical WCF boundary.

public class DomainMergeInjection : ConventionInjection
{
    private readonly Repository _repository;
    private readonly Dictionary<string, object> _potentialParentObjectDump;
    private readonly Cache<Type, Type> _entityTypesAndKeysCache;

    public DomainMergeInjection(Repository repository)
    {
        _repository = repository;
        _potentialParentObjectDump = new Dictionary<string, object>();
        _entityTypesAndKeysCache = new Cache<Type, Type>();
    }

    protected override bool Match(ConventionInfo c)
    {
        return c.SourceProp.Name == c.TargetProp.Name;
    }

    protected override object SetValue(ConventionInfo c)
    {
        if(c.SourceProp.Value == null)
            return null;

        //for value types and string just return the value as is 
        if(c.SourceProp.Type.IsSimple())
            return c.SourceProp.Value;

        //TODO: Expand on this to handle IList/IEnumerable (i.e. the non-generic collections and arrays).
        //handle arrays
        if(c.SourceProp.Type.IsArray)
        {
            var sourceArray = c.SourceProp.Value as Array;
            // ReSharper disable PossibleNullReferenceException
            var clonedArray = sourceArray.Clone() as Array;
            // ReSharper restore PossibleNullReferenceException

            for(int index = 0; index < sourceArray.Length; index++)
            {
                var sourceValueAtIndex = sourceArray.GetValue(index);

                //Skip null and simple values that would have already been moved in the clone.
                if(sourceValueAtIndex == null || sourceValueAtIndex.GetType().IsSimple())
                    continue;

                // ReSharper disable PossibleNullReferenceException
                clonedArray.SetValue(RetrieveComplexSourceValue(sourceValueAtIndex), index);
                // ReSharper restore PossibleNullReferenceException
            }

            return clonedArray;
        }

        //handle IEnumerable<> also ICollection<> IList<> List<>
        if(c.SourceProp.Type.IsGenericEnumerable())
        {
            var t = c.SourceProp.Type.GetGenericArguments()[0];

            if(t.IsSimple())
                return c.SourceProp.Value;

            var tlist = typeof(List<>).MakeGenericType(t);
            dynamic list = Activator.CreateInstance(tlist);

            var addMethod = tlist.GetMethod("Add");

            foreach(var sourceItem in (IEnumerable)c.SourceProp.Value)
            {
                addMethod.Invoke(list, new[] { RetrieveComplexSourceValue(sourceItem) });
            }

            return list;
        }

        //Get a source value that is in the right state and is tracked if needed.
        var itemStateToInject = RetrieveComplexSourceValue(c.SourceProp.Value);
        return itemStateToInject;
    }

    private object RetrieveComplexSourceValue(object source)
    {
        //If the source is a non-tracked type, or the source is a new value, then return its value.
        if(!source.ImplementsIEntity(_entityTypesAndKeysCache) || source.IsEntityIdNull(_entityTypesAndKeysCache))
            return source;

        object sourceItemFromContext;

        //Handle recursive entities, this could probably be cleaned up.
        if(source.ImplementsIRecursiveEntity())
        {
            var itemKey = source.GetEntityIdString(_entityTypesAndKeysCache) + " " + ObjectContext.GetObjectType(source.GetType());

            //If we have a context item for this key already, just return it.  This solves a recursion problem with self-linking items.
            if(_potentialParentObjectDump.ContainsKey(itemKey))
                return _potentialParentObjectDump[itemKey];

            //Get the source from the context to ensure it is tracked.
            sourceItemFromContext = GetSourceItemFromContext(source);

            //Add the class into the object dump in order to avoid any infinite recursion issues with self-linked objects
            _potentialParentObjectDump.Add(itemKey, sourceItemFromContext);
        }
        else
            //Get the source from the context to ensure it is tracked.
            sourceItemFromContext = GetSourceItemFromContext(source);

        //Recursively use this injection class instance to inject the source state on to the context source state.
        var itemStateToInject = sourceItemFromContext.InjectFrom(this, source);

        return itemStateToInject;
    }

    private object GetSourceItemFromContext(object source)
    {
        if(source == null)
            return null;

        //Using dynamic here to "AutoCast" to an IEntity<>.  We should have one, but it important to note just in case.
        dynamic sourceEntityValue = source;
        var sourceEntityType = ObjectContext.GetObjectType(source.GetType());
        var sourceKeyType = sourceEntityType.GetEntityKeyType();

        var method = typeof(DomainMergeInjection).GetMethod("GetFromContext", BindingFlags.Instance | BindingFlags.NonPublic);
        var generic = method.MakeGenericMethod(sourceEntityType, sourceKeyType);

        var sourceItemFromContext = generic.Invoke(this, new object[] { new object[] { sourceEntityValue.Id } });
        return sourceItemFromContext;
    }

    // ReSharper disable UnusedMember.Local
    private TItem GetFromContext<TItem, TKey>(object[] keys) where TItem : class, IEntity<TKey>
    // ReSharper restore UnusedMember.Local
    {
        var foundItem = _repository.GetDbSet<TItem>().Find(keys);

        return foundItem;
    }
}

public static class EntityTypeExtensions
{
    /// <summary>
    /// Determines if an object instance implements IEntity.
    /// </summary>
    /// <param name="entity"></param>
    /// <param name="entityCache">A cache to hold types that do implement IEntity.  If the cache does not have the Type and the Type does implement IEntity, it will add the type to the cache along with the </param>
    /// <returns></returns>
    public static bool ImplementsIEntity(this object entity, Cache<Type, Type> entityCache = null)
    {
        //We need to handle getting the proxy type if this is an EF Code-First proxy.
        //Please see for more info: http://msdn.microsoft.com/en-us/library/dd456853.aspx
        var entityType = ObjectContext.GetObjectType(entity.GetType());

        if(entityCache != null && entityCache.Has(entityType))
            return true;

        var implementationOfIEntity = entityType.GetInterfaces().FirstOrDefault(x => x.IsGenericType && x.GetGenericTypeDefinition() == typeof (IEntity<>));

        if(implementationOfIEntity == null)
            return false;

        if(entityCache != null)
        {
            var keyType = implementationOfIEntity.GetGenericArguments()[0];
            entityCache.Fill(entityType, keyType);
        }

        return true;
    }

    /// <summary>
    /// Determines if an object instances implements IRecurisveEntity
    /// </summary>
    /// <param name="entity"></param>
    /// <returns></returns>
    public static bool ImplementsIRecursiveEntity(this object entity)
    {
        //We need to handle getting the proxy type if this is an EF Code-First proxy.
        //Please see for more info: http://msdn.microsoft.com/en-us/library/dd456853.aspx
        var entityType = ObjectContext.GetObjectType(entity.GetType());

        var implementsIRecursiveEntity = entityType.GetInterfaces().Any(x => x.IsGenericType && x.GetGenericTypeDefinition() == typeof(IRecursiveEntity<>));

        return implementsIRecursiveEntity;
    }

    /// <summary>
    /// Determines whether or not an Entity Id is null.  Will throw an exception if a type that does not implement IEntity is passed through.
    /// </summary>
    /// <param name="entity"></param>
    /// <param name="entityCache"></param>
    /// <returns></returns>
    public static bool IsEntityIdNull(this object entity, Cache<Type, Type> entityCache = null)
    {
        bool isEntityIdNull = ExecuteEntityIdMethod<bool>("IsEntityIdNull", entity, entityCache);

        return isEntityIdNull;
    }

    /// <summary>
    /// Determines whether or not an Entity Id is null.  Will throw an exception if a type that does not implement IEntity is passed through.
    /// </summary>
    /// <param name="entity"></param>
    /// <param name="entityCache"></param>
    /// <returns></returns>
    public static string GetEntityIdString(this object entity, Cache<Type, Type> entityCache = null)
    {
        string entityIdString = ExecuteEntityIdMethod<string>("GetEntityIdString", entity, entityCache);

        return entityIdString;
    }

    private static T ExecuteEntityIdMethod<T>(string methodName, object entityInstance, Cache<Type, Type> entityCache = null)
    {
        if(!entityInstance.ImplementsIEntity(entityCache))
            throw new ArgumentException(string.Format("Parameter entity of type {0} does not implement IEntity<>, and so ist not executable for {1}!", entityInstance.GetType(), methodName));

        //We need to handle getting the proxy type if this is an EF Code-First proxy.
        //Please see for more info: http://msdn.microsoft.com/en-us/library/dd456853.aspx
        var entityType = ObjectContext.GetObjectType(entityInstance.GetType());
        var keyType = entityCache != null ? entityCache[entityType] : entityType.GetEntityKeyType();

        var method = typeof(EntityTypeExtensions).GetMethod(methodName, BindingFlags.Static | BindingFlags.NonPublic);
        var generic = method.MakeGenericMethod(keyType);

        T returnValue = (T)generic.Invoke(null, new[] { entityInstance });

        return returnValue;
    }

    private static string GetEntityIdString<TKey>(IEntity<TKey> entity)
    {
        var entityIdString = entity.Id.ToString();

        return entityIdString;
    }

    private static bool IsEntityIdNull<TKey>(IEntity<TKey> entity)
    {
        //We need to handle getting the proxy type if this is an EF Code-First proxy.
        //Please see for more info: http://msdn.microsoft.com/en-us/library/dd456853.aspx
        var entityType = ObjectContext.GetObjectType(entity.GetType());

        if(entityType.IsPrimitive)
            return false;

        //NOTE:  We know that this entity type is NOT primitive, therefore we can cleanly test for null, and return properly.
        // ReSharper disable CompareNonConstrainedGenericWithNull
        var entityIdIsNull = entity.Id == null;
        // ReSharper restore CompareNonConstrainedGenericWithNull

        return entityIdIsNull;
    }

    public static Type GetEntityKeyType(this Type typeImplementingIEntity)
    {
        var implementationOfIEntity = typeImplementingIEntity.GetInterfaces().FirstOrDefault(x => x.IsGenericType && x.GetGenericTypeDefinition() == typeof(IEntity<>));

        if(implementationOfIEntity == null)
            throw new ArgumentException(string.Format("Type {0} does not implement IEntity<>", typeImplementingIEntity));

        var keyType = implementationOfIEntity.GetGenericArguments()[0];
        return keyType;
    }
}

public interface IEntity<TKey>
{
    TKey Id { get; set; }
}


public interface IRecursiveEntity<TKey> : IEntity<TKey>
{
    IRecursiveEntity<TKey> Parent { get; }
    IEnumerable<IRecursiveEntity<TKey>> Children { get; }
}