Recursive Entity Update

Question

I have an entity which holds a list of entities (same as root entity) to represent a Folder structure:

public class SopFolder
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime? LastUpdated { get; set; }
    public int Status { get; set; }
    public virtual ICollection<SopField> SopFields { get; set; }
    public virtual ICollection<SopFolder> SopFolderChildrens { get; set; }
    public virtual ICollection<SopBlock> Blocks { get; set; }
    public virtual ICollection<SopReview> Reviews { get; set; }
}

This entity is stored in my DB using Code-First Approach which is working fine. I then print the entity to a KendoUI Treeview, let the user modify it and on "save" post it back to the Server to an Action as IEnumerable<TreeViewItemModel> items.

I then look for the ROOT entity with all it's children (there is only one root) and convert it back into an SopFolder object.

To get the full object updated in the database I do the following:

 List<SopFolder> sopfolderlist = ConvertTree(items.First());

        SopFolder sopfolder = sopfolderlist[0];

        if (ModelState.IsValid)
        {
            SopFolder startFolder = new SopFolder { Id = sopfolder.Id };

            //db.SopFolders.Attach(startFolder);
           // db.SopFolders.Attach(sopfolder);

            startFolder.Name = sopfolder.Name;
            startFolder.LastUpdated = sopfolder.LastUpdated;
            startFolder.SopFields = sopfolder.SopFields;
            startFolder.SopFolderChildrens = sopfolder.SopFolderChildrens;
            startFolder.Status = sopfolder.Status;

            db.Entry(startFolder).State = EntityState.Modified;

            db.SaveChanges();
            return Content("true");
        }

However this is not working. The model is not updated at all. If I shift the "entityState.Modified" before the modifications, it just creates a complete fresh duplicate of my data in the database (modified of course).

Is my approach correct or do I have to go a different path? What am I missing here? I guess there is another "hidden" id which lets the EF map the entities to the db entries but I am not sure about this. Thanks for help!

UPDATE: Instead of creatinga new instance of SopFolder I also tried db.SopFolders.Find(sopfolder.Id) and this works for entries with no children. If I have entities with children, it creates a duplicate.

Regards, Marcus

Answer 1

This is typical Disconnected Graph scenario. Please see this question for possible solutions: Disconnected Behavior of Entity Framework when Updating Object Graph

You have already figure out the first solution - that is: update entities separately. Actually, what you should do is to fetch the original data from database and then do comparison of what have changed. There are some generic ways of doing that, some of them are described in "Programming EF DbContext" book by J.Lerman, which I strongly recommend to you before doing more coding using EF.

P.S. IMHO this is the worse downside of EF.

Answer 2

I recommend you to create your entity model with ParentId, not children object list. When you need treeview model collect it with recursive function from database.

public class SopFolder
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime? LastUpdated { get; set; }
    public int Status { get; set; }
    public virtual ICollection<SopField> SopFields { get; set; }

    //public virtual ICollection<SopFolder> SopFolderChildrens { get; set; }
    public int? ParentFolderId { get; set; }

    public virtual ICollection<SopBlock> Blocks { get; set; }
    public virtual ICollection<SopReview> Reviews { get; set; }
}

When you create children folders, select it's parent, so collect your data. In childrens case try this :

List<SopFolder> sopfolderlist = ConvertTree(items.First());

        SopFolder sopfolder = sopfolderlist[0];

        if (ModelState.IsValid)
        {
            SopFolder startFolder = new SopFolder { Id = sopfolder.Id };

            //db.SopFolders.Attach(startFolder);
           // db.SopFolders.Attach(sopfolder);

            startFolder.Name = sopfolder.Name;
            startFolder.LastUpdated = sopfolder.LastUpdated;
            startFolder.SopFields = sopfolder.SopFields;
            startFolder.SopFolderChildrens = sopfolder.SopFolderChildrens;

            foreach (var child in sopfolder.SopFolderChildrens)
            {
               db.SopFolders.CurrentValues.SetValues(child);
               db.SaveChanges();
            }

            startFolder.Status = sopfolder.Status;
            db.Entry(startFolder).State = EntityState.Modified;
            db.SaveChanges();
            return Content("true");
        }

Answer 3

Replace SopFolder startFolder = new SopFolder { Id = sopfolder.Id }; with

 SopFolder startFolder = db.SopFolders.FirstOrDefault(s=>s.Id.Equals(sopfolder.Id));

 // then validate if startFolder != null

Answer 4

i have come up with this solution and it has worked remarkably.

    /// <summary>
/// simple update method that will help you to do a full update to an aggregate graph with all related entities in it.
/// the update method will take the loaded aggregate entity from the DB and the passed one that may come from the API layer.
/// the method will update just the eager loaded entities in the aggregate "The included entities"
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="context"></param>
/// <param name="newEntity">The De-Attached Entity</param>
public static void UpdateGraph<T>(this DbContext context, T newEntity) where T : class
{
    var existingEntity = context.Set<T>().FindAttachedEntry(newEntity);
    UpdateGraph(context, newEntity, existingEntity, null);
}
private static T? FindAttachedEntry<T>(this DbSet<T> set, T entity) where T : class
{
    var primaryKeys = set.EntityType.FindPrimaryKey()!.Properties
        .Select(x => new { getter = x.GetGetter(), comparer = x.GetKeyValueComparer() })
        .ToArray();

    return set.Local
        .FirstOrDefault(local => primaryKeys.All(comparer =>
                comparer.comparer.Equals(comparer.getter.GetClrValue(local), comparer.getter.GetClrValue(entity))
            )
        );
}
private static void UpdateGraph<T>(this DbContext context, T? newEntity, T? existingEntity,
    string? parentAggregateTypeName)
    where T : class
{
    if (existingEntity == null && newEntity != null)
    {
        context.Entry(newEntity).State = EntityState.Added;
        return;
    }

    if (newEntity == null && existingEntity != null)
    {
        context.Entry(existingEntity).State = EntityState.Deleted;
        return;
    }

    if (existingEntity is null || newEntity is null)
    {
        throw new UnreachableException();
    }

    var existingEntry = context.Entry(existingEntity);
    existingEntry.CurrentValues.SetValues(newEntity);

    foreach (var navigationEntry in existingEntry.Navigations.Where(n =>
                 n.IsLoaded && n.Metadata.ClrType.FullName != parentAggregateTypeName))
    {
        var entityTypeName = existingEntry.Metadata.ClrType.FullName;
        var newValue = existingEntry.Entity.GetType().GetProperty(navigationEntry.Metadata.Name)
            ?.GetValue(newEntity);

        var existingValue = navigationEntry.CurrentValue;
        //if (navigationEntry.Metadata.IsCollection()) causes Error CS1929  'INavigationBase' does not contain a definition for 'IsCollection' and the best extension method overload 'NavigationExtensions.IsCollection(INavigation)' requires a receiver of type 'INavigation'   
        //use instead https://learn.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.changetracking.collectionentry?view=efcore-7.0
        if (navigationEntry is CollectionEntry)
        {
            var newItems = newValue as IEnumerable<object> ?? Array.Empty<object>();
            var existingItems = (existingValue as IEnumerable<object>)?.ToList() ?? new List<object>();

            // get new and updated items
            foreach (var newItem in newItems)
            {
                var key = context.Entry(newItem).GetPrimaryKeyValues();
                var existingItem =
                    existingItems.FirstOrDefault(x => context.Entry(x).GetPrimaryKeyValues().SequenceEqual(key));
                if (existingItem is not null)
                {
                    existingItems.Remove(existingItem);
                }

                UpdateGraph(context, newItem, existingItem, entityTypeName);
            }

            foreach (var existingItem in existingItems)
            {
                UpdateGraph(context, null, existingItem, entityTypeName);
            }
        }
        else
        {
            // the navigation is not a list
            UpdateGraph(context, newValue, existingValue, entityTypeName);
        }
    }
}

this is how i would normally use it:

// fetch the entity from the db and load it into the changes tracker
    var model = _db.Foos.FirstOrDefault(x => x.Id == dto.Id);
    var updatedModel = dto.Map();
    // the update graph method will find the loaded entity and 
    // compare its properties against the updatedModel. If the 
    // model was not loaded (it does not exist) it will perform an
    // insertion instead of an update
    _db.UpdateGraph(updatedModel); 
    await _db.SaveChangesAsync();