Entity Framework Collection was modified; enumeration operation may not execute

Question

I'm currently using EF 4.0. My objective is to delete a child collection and add new ones to same parent.

 public void AddKids(int parentId, Kids newKids)  {     using (ModelContainer context = new ModelContainer(connectionString))     {         using (TransactionScope scope = new TransactionScope())         {             var query = from Parent _parent in context.Parents                         where _parent.ParentId == parentId select _parent;              Parent parent = query.Single();             while (parent.Kids.Any())             {                 context.Kids.DeleteObject(parent.Kids.First());             }              if (newKids != null)             {                 foreach (Kid _kid in newKids)                 {                     parent.Kids.Add(new Kid                     {                         Age = _kid.Age,                         Height = _kid.Height                     });                 }             }             scope.Complete();         }         context.SaveChanges(); //Error happens here     } } 

The error is as from the title: Collection was modified; enumeration operation may not execute.

Any help would be appreciated.

Answer 1

You are seeing this because you delete objects from a collection that currently has active operations on. More specifically you are updating the Kids collection and then executing the Any() operator on it in the while loop. This is not a supported operation when working with IEnumerable instances. What I can advice you to do is rewrite your while as this:

parent.Kids.ToList().ForEach(r => context.Kids.DeleteObject(r)); 

I hope that helps.