I'm having an issue updating an entity with multiple related entities. I've got a very simple model which consists of an article entity and a list of categories the article can be related to. You can choose from a check box list which of these categories are associated to it...which works fine. The problem crops up when I actually come to update an existing entity using the dbContext. As I am updating this entity, I have already detached it from the context ready to re-attach it later so the update can execute properly. I can see that after I posting the model, the category(s) are being added to the article entity just fine and it looks like it updates in the repository with no errors occurring. When I look in the database the article has updated as normal but the category(s) have not. Here is my (simplified) update code... public virtual bool Attach(T entity) { _dbContext.Entry(entity).State = EntityState.Modified; _dbSet.Attach(entity); return this.Commit(); } Any help will be much appreciated.