EF5 Many To Many update disconnected scenario

Question

I didn't find yet a good solution to this problem (similar ticket here EF5 update disconnected graph (n-tier) one-to-many).

I found and followed this example: http://entityframeworktutorial.net/update-many-to-many-entities-in-entity-framework.aspx#.UTBeTDBhif8.

This works just fine, but it creates a duplicate of the related entities (with sql profiler I saw the Insert into RelatedEntities .. I would expected just an insert / update on the MyEntities_Related join table and I don't understand why EF makes an insert on the RelatedEntities table :(

And here is my code:

public void AddOrUpdate(MyEntity entity) {
    var dbEntity = _context.MyEntities
      .Include(e => e.RelatedEntitis)
      .Where(e => e.ID == entity.ID)
      .SingleOrDefault();

    var newRelated = entity.RelatedEntitis.ToList<RelatedEntity>();
    var dbRelated = dbEntity.RelatedEntity.ToList<RelatedEntity>();

    _context.Entry(dbEntity).CurrentValues.SetValues(entity);

    var comparer = new EqualityComparer();
    var addedRelated = newRelated.Except(dbRelated, comparer).ToList<RelatedEntity>();
    var deletedRelated = dbRelated.Except(newRelated, comparer).ToList<RelatedEntity>();

    addedRelated.ForEach(e => dbEntity.RelatedEntity.Add(e));
    deletedRelated.ForEach(e => dbEntity.RelatedEntity.Remove(e));
}

public class EqualityComparer : IEqualityComparer<RelatedEntity>
{
    public int GetHashCode(RelatedEntity obj)
    {
      return (obj == null) ? 0 : obj.ID.GetHashCode();
    }

    public bool Equals(RelatedEntity x, RelatedEntity y)
    {
      if (ReferenceEquals(x, y)) return true;
      if (x == null || y == null) return false;
      return x.ID == y.ID;
    }
}

the db schema is like the following:

|------------------|
| Table MyEntities |
|------------------| 
| int ID //PK      |
|------------------| 


|--------------------------|
| Table MyEntities_Related |
|--------------------------|
| int MyEntityID           |
| int RelatedID            | 
|--------------------------|


|-----------------------|
| Table RelatedEntities |
|-----------------------|
| int RelatedID //PK    |
| string Name           | 
|-----------------------|

any help is appreciated :)

Answer 1

SOLUTION I don't know if it's the best, but it works for me and I think it has sense. EF creates a duplicate of the relatedentities because they were detached, I changed my code in this way:

public void AddOrUpdate(MyEntity entity) {
    var dbEntity = _context.MyEntities
      .Include(e => e.RelatedEntitis)
      .Where(e => e.ID == entity.ID)
      .SingleOrDefault();

    //replace entities with those taken from the context
    var relatedEntities = _context.RelatedEntities;
    var detachedEntities = entity.RelatedEntities;
    entity.RelatedEntities = new List<RelatedEntity>();
    foreach (var ent in detachedEntities)
    {
      entity.RelatedEntities.Add(relatedEntities .Where(e => e.ID == hop.ID).SingleOrDefault());
    }

    var newRelated = entity.RelatedEntitis.ToList<RelatedEntity>();
    var dbRelated = dbEntity.RelatedEntity.ToList<RelatedEntity>();

    _context.Entry(dbEntity).CurrentValues.SetValues(entity);
    _context.Entry(dbEntity.RelatedEntity).CurrentValues.SetValues(entity.RelatedEntitis);

    var comparer = new EqualityComparer();
    var addedRelated = newRelated.Except(dbRelated, comparer).ToList<RelatedEntity>();
    var deletedRelated = dbRelated.Except(newRelated, comparer).ToList<RelatedEntity>();

    addedRelated.ForEach(e => dbEntity.RelatedEntity.Add(e));
    deletedRelated.ForEach(e => dbEntity.RelatedEntity.Remove(e));
}