Question

following function return List of records

 public IList<T> GetAll()
 {
   return db.TabMasters.ToList<T>();
 }

Error:
‘System.Data.Objects.ObjectSet’ does not contain a definition for ‘ToList’ and the best extension method overload ‘System.Linq.Enumerable.ToList(System.Collections.Generic.IEnumerable)’ has some invalid arguments

Answer 1

IList<T> is the Interface that is used by List<T> and several other similar containers. You can’t return an Interface itself – you have to return an object that implements IList<T>. Though I don’t know exactly what your situation is, the best choice is most likely List<T>.

Also, you have a problem with the generic Type T. If you want the method to be generic, then you have to cast all the values in db.TabMasters to Type T. This gets tricky because you’ll have to limit the possible Types used for T to prevent Exceptions caused by an invalid cast (see here). If you only need to return one type, then you should define that as the return type instead of using T. For example, lets say that all the values in db.TabMasters are string. Then you’d use:

public IList<string> GetAll()
{
    return db.TabMasters.ToList();
}

If you really need the method to be generic, then you have to cast the values in db.TabMasters to the type you want to return:

public IList<T> GetAll<T>()
{
    return db.TabMasters.Cast<T>().ToList();
}

Note that if the object type stored in db.TabMasters can’t be cast to T, the method will throw an InvalidCastException.

Happy Coding!