Question

I have a class, and I declare it like this:

public class WhereOrCondition<T> : WhereCondition<T>

The generic type T is the same for both classes. I am not sure how to declare my classes correctly so that the Generic type used for WhereOrCondition is also used in WhereCondition.

Declaring my class in this way gives me the following error:

Error 1 The type 'T' cannot be used as type parameter 'T' in the generic type or method 'BrainStorm.WhereCondition<T>'. There is no boxing conversion or type parameter conversion from 'T' to 'BrainStorm.DatabaseObject'.

Any ideas on how I can declare my class correctly?

EDIT

The WhereCondition class is declared like so:

public class WhereCondition<T> : IEnumerable<KeyValuePair<string, object>> where T : DatabaseObject 

Answer 1

You need to put the same where condition on WhereOrCondition<T> so it looks like

public class WhereOrCondition<T> : WhereCondition<T> where T: DatabaseObject

The rule is a where clause on a sub class must be the same or more restrictive than a where clause on a base class.

What this says is WhereOrCondition<T> has WhereCondition<T> for a sub class and T must be a DatabaseObject (or a subclass).

Your code in the comment public class WhereAndCondition<T> where T: WhereCondition<T> is something completly different. That says that T must be a WhereCondition<T> which cannot be true.