ToList method not available for TrackableCollection

问题

We are working with Trackable Entities on top of EF 4.0.

In order to delete an Entity with all its dependent entities I'm writing a generic DeleteDependentEntities to be called from the Delete method in the EntityManager. (We don't, or don't want to, rely on a CASCADE DELETE to be set on the relations in our database.) The DeleteDependentEntities scans recursevly all Children of the subjected entitySet.

In order to keep it generic, so that it can be used for all entities throughout the project I'm using dynamic types.

The method is as follows:

private void DeleteDependentEntities(dynamic entitySet, dynamic context)
{
  if (entitySet != null)
  {
    foreach (dynamic item in entitySet.ToList())
    {
      // 1. Scan object for children and delete children
      ProcessChildren(item, context);

      // 2. Delete this object
      context.DeleteObject(item);
    }
  }
}

It compiles OK, but at runtime I get the following error:

'SLS.AnimalIntakeMgmt.DataTypes.TrackableCollection' does not contain a definition for 'ToList'

Hence the type inference worked OK. Problem with the ToList definition is weird since TrackableCollection is based on ObservableCollection which in its turn is based on Collection.

The ToList is necessary because otherwise the foreach loop fails because the collection is modified within the loop.

All suggestions are welcome!

回答1:

The problem is that dynamics don't work with extension methods. The runtime only looks for methods defined on the dynamic object itself.
You need to call ToList as a static method:

foreach (dynamic item in Enumerable.ToList(entitySet))

But I really think you should use generics if possible at all.

来源：https://stackoverflow.com/questions/6663593/tolist-method-not-available-for-trackablecollection