DbSet.Remove Method (Object)
Marks the given entity as Deleted such that it will be deleted from the database when SaveChanges is called. Note that the entity must exist in the context in some other state before this method is called.
Assembly: EntityFramework (in EntityFramework.dll)
Note that if the entity exists in the context in the Added state, then this method will cause it to be detached from the context. This is because an Added entity is assumed not to exist in the database such that trying to delete it does not make sense.