def type_selection
      klasses = klass._types
      if klasses.size > 1
        { _type: { "$in" => klass._types }}
      else
        { _type: klass._types[0] }
      end
    end
def type_selection
      klasses = klass._types
      if klasses.size > 1
        { _type: { "$in" => klass._types }}
      else
        { _type: klass._types[0] }
      end
    end
Get the selector for type selection.

 @api private

 @example Get a type selection hash.
   criteria.type_selection

 @return [ Hash ] The type selection.

 @since 3.0.3