Make EntityEntryGraphIterator publicly usable

[voroninp]

Currently EntityEntryGraphNode constructor is internal and depends on internal types.

---

I want to automatically change concurrency token of an aggregate root when any of its entities changes.
It's is possible that AR entity has no changes, but child entities do. So I'd like to traverse the graph and check whether there are modified, added, or deleted entities. And if yes, Version property should be incremented.

There's is a TrackGraph method to adjust tracking for disconnected entities, but I want to traverse already attached graph. Do I have to write this functionality myself using EntityEntry api for accessing navigations?

I am also curious how I detect additions and removals of child entities? Is NavigationEntry.IsModified enough for this?

[voroninp]

Ended up having such implementation (not tested yet):

private bool GraphHasChanges(TAggregateRoot aggregateRoot) => GraphHasChangesRecursive(aggregateRoot, new HashSet<object>());

private bool GraphHasChangesRecursive(object rootEntity, HashSet<object> checkedEntities)
{
    // prevents cycles.
    if (checkedEntities.Contains(rootEntity))
    {
        return false;
    }

    var rootEntityEntry = _dbContext.Entry(rootEntity);
    if (rootEntityEntry.State == EntityState.Detached)
    {
        throw new InvalidOperationException($"Root entity of type '{rootEntity.GetType()}' is not tracked.");
    }

    checkedEntities.Add(rootEntityEntry);

    if (rootEntityEntry.State != EntityState.Unchanged)
    {
        return true;
    }

    var changesInChildEntities = rootEntityEntry.Navigations.Any(_ => _.IsModified || _.CurrentValue switch
    {
        IEnumerable seq => seq.OfType<object>().Any(entity => GraphHasChangesRecursive(entity, checkedEntities)),
        object entity => GraphHasChangesRecursive(entity, checkedEntities)
    });

    if (changesInChildEntities)
    {
        return true;
    }

    return false;
}

[ajcvickers]

@voroninp Have you considered using the IEntityEntryGraphIterator service?

[voroninp]

@ajcvickers I was not aware of it, thanks. Should I resolve it with service provider, or is it accessible through DbContext?

[voroninp]

@ajcvickers

handleNode:

Func<EntityEntryGraphNode<TState>,Boolean>

Is returned bool for signaling whether to continue traversal?

[ajcvickers]

context.GetService. Yes.

[voroninp]

you won't get rid of me that easy =)

Constructor of EntityEntryGraphNode has this documentation:

This is an internal API that supports the Entity Framework Core infrastructure and not subject to the same compatibility standards as public APIs. It may be changed or removed without notice in any release. You should only use it directly in your code with extreme caution and knowing that doing so can result in application failures when updating to a new Entity Framework Core release.

And not much about its arguments. =(
Could you elaborate on them, please?

[ajcvickers]

@voroninp Don't call the constructor. Use CreateNode.

[voroninp]

Where can CreateNode method be found? It's virtual on EntityEntryGraphNode, so I need to have a node firts.

[ajcvickers]

@voroninp You are right. We should look into making this available publicly. For now, you can use TrackGraph, without actually tracking anything. Here's an example, based on this test:

public class Blog
{
    public int Id { get; set; }
    public string Name { get; set; }

    public ICollection<Post> Posts { get; } = new List<Post>();
}

public class Post
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }

    public Blog Blog { get; set; }
}

public class SomeDbContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer(Your.ConnectionString)
            //.LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

    public virtual DbSet<Blog> Blogs { get; set; }
}

public class Program
{
    public static void Main()
    {
        using (var context = new SomeDbContext())
        {
            context.Database.EnsureDeleted();
            context.Database.EnsureCreated();

            context.Add(new Blog {Posts = {new(), new()}});

            context.SaveChanges();
        }

        using(var context = new SomeDbContext())
        {
            var blog = context.Blogs.Include(e => e.Posts).Single();

            var visited = new HashSet<object>();
            var traversal = new List<string>();

            context.ChangeTracker.TrackGraph(
                blog,
                visited,
                node =>
                {
                    if (node.NodeState.Contains(node.Entry.Entity))
                    {
                        return false;
                    }

                    node.NodeState.Add(node.Entry.Entity);

                    traversal.Add(NodeString(node));

                    return true;
                });

            foreach (var visit in traversal)
            {
                Console.WriteLine(visit);
            }
        }
    }

    private static string NodeString(EntityEntryGraphNode node)
        => EntryString(node.SourceEntry)
           + " ---"
           + node.InboundNavigation?.Name
           + "--> "
           + EntryString(node.Entry);

    private static string EntryString(EntityEntry entry)
        => entry == null
            ? "<None>"
            : entry.Metadata.DisplayName()
              + ":"
              + entry.Property(entry.Metadata.FindPrimaryKey().Properties[0].Name).CurrentValue;
}

Output:

<None> -----> Blog:1
Blog:1 ---Posts--> Post:1
Blog:1 ---Posts--> Post:2