def add_constraints(list)
      list = Array.wrap(list).select { |m| m.is_a?(Parse::Constraint) }
      @where = @where + list
      self
    end
def add_constraints(list)
      list = Array.wrap(list).select { |m| m.is_a?(Parse::Constraint) }
      @where = @where + list
      self
    end
Combine a list of {Parse::Constraint} objects
 @param list [Array<Parse::Constraint>] an array of Parse::Constraint subclasses.
 @return [self]