Question

I have a generic method in my repository which updates a property common to all the objects in my edmx model:

    private void SetUpdateParams(TEntity entity)
    {
        PropertyInfo prop = typeof(TEntity).GetProperty("CommonProperty");

        prop.SetValue(entity, "Some Value", null);
    }

This property is called by the add, update and delete methods. Example:

    public void Delete(TEntity entity)
    {
        SetUpdateParams(entity);
        _objectSet.DeleteObject(entity);
        txDB.SaveChanges();
    }

This all works fabulously well, until I try to include children in a cascade delete scenario. Since the sprocs I have to use require that this certain property is set, I must now recurse through the relationships and set this property on any loaded children in the ObjectSet. Problem is I can’t seem to figure out any way to do that. Has anyone done something like this before?

Answer 1

It’s not the easiest solution and can be a tad tedious, but I implemented what you’re needing in a project of mine by spanning the object graph, updating the property as I found it, and keeping track of what I’ve visited. It gave great flashbacks to undergrad computer science classes. =)

Essentially, take your object, get its properties, and push them on a stack. For each property on the stack, test if it’s the property you’re looking for. Handle if match, ignore if simple data type, add to stack if complex object.

A couple of things that aided me in my implementation:

• Create an interface containing the property you’re looking for and make all classes that have the property implement it. It makes it easier to interrogate your classes with reflection.
• Try to be smart with the types of complex properties you throw on the stack to be traversed. I used an interface that designates that this complex type may have a property that needs to be updated.
• Use something (I used a HashSet) to mark objects you’ve seen and help prevent circular reference traversals.
• I have this functionality as part of a BaseContext’s (inheriting EF’s ObjectContext) custom Save() method. I call this fixup and then call base.SaveChanges().

Like I said, not an easy, straightforward question, but my code handles deep object graphs and updates multiple property instances. If interested, I can follow-up with some pseudo code.

---

EDIT/UPDATE

As the code shows, I’m interested in updating current UserName and DateTime values for any number of objects that may appear in the graph.

Notes:

• Interface IInsertedInfo contains the properties that we need to update. So if an object implements IInsertedInfo, we know to update its properties.
• An object that implements IRequiresCurrentUserDateTime is one that has, somewhere in its graph, an object that implements IInsertedInfo.
• This is done in context of a save with EF. I’m interrogating the ObjectStateManager for objects that need to be saved/updated.

I don’t claim this to be the most succinct solution, but it works fine for me. Additionally, checks for IRequiresCurrentUserDateTime and other filters (some omitted for clarity’s sake) are used solely to keep the search space manageable and to avoid spanning .NET objects, non-class types, etc.

private void HandleInsertedUserNames(string userName)
{
    // grab any entity that requires a current user value
    var requiresUser = this.ObjectStateManager.GetObjectStateEntries(EntityState.Added | EntityState.Deleted | EntityState.Modified)
                                              .Where(ose => ose.Entity is IRequiresCurrentUserDateTime
                                                            || ose.Entity is IInsertedInfo)
                                              .Select(ose => ose.Entity);

    var now = DateTime.Now;
    object current;
    var seen = new HashSet<object>();
    var stack = new Stack<object>();
    // for each entity requiring a current user value...
    foreach (var obj in requiresUser)
    {
        // traverse its object graph and update any objects that implement IRequiresCurrentUserDateTime
        stack.Push(obj);
        while (stack.Count > 0)
        {
            current = stack.Pop();
            if (current != null && !seen.Contains(current))
            {
                // mark object as seen
                seen.Add(current);
                // if object implements IInsertedInfo, then set its property
                if (current is IInsertedInfo)
                {
                    (current as IInsertedInfo).UserName = userName;
                    (current as IInsertedInfo).DateTime = now;
                    // we can continue on to the next object in the stack if we've hit an IInsertedInfo
                    continue;
                }

    // REMOVED FILTERING TESTS I USED TO REDUCE SEARCH SPACE (e.g.: is modified?)

                if (current is IRequiresCurrentUserDateTime)
                {
                    // push any instance, public properties and push them to the stack
                    current.GetType().GetProperties(BindingFlags.Instance | BindingFlags.Public)
    // HERE YOU CAN FILTER THE PROPERTY COLLECTION VIA WHERE CLAUSES (e.g.: only certain namespace, type, etc)
                           // select the actual value of the property
                           .Select(type => type.GetValue(current, null))
                           // further filter -- only values NOT already in the requiresUser
                           // list and those that implement IRequiresCurrentUserDateTime or IInsertedInfo
                           .Where(value => !requiresUser.Contains(value)
                                           && (value is IRequiresCurrentUserDateTime
                                               || value is IInsertedInfo))
                           .ToList().ForEach(stack.push);
                }
            }
        }
    }

}