def valid_columns(valid_columns, columns)
			columns.each do |col|

				if col.is_a?(String)
					if !valid_columns.value?(col)
						raise Exception.new("Invalid column value '#{col}'")
					end 
				elsif col.is_a?(Symbol)
					if !valid_columns.key?(col.to_s)
						raise Exception.new("Invalid column name '#{col}'")
					end
				end
			end
			return true
		end
def valid_columns(valid_columns, columns)
			columns.each do |col|

				if col.is_a?(String)
					if !valid_columns.value?(col)
						raise Exception.new("Invalid column value '#{col}'")
					end 
				elsif col.is_a?(Symbol)
					if !valid_columns.key?(col.to_s)
						raise Exception.new("Invalid column name '#{col}'")
					end
				end
			end
			return true
		end
Internal : Validates the specified columns at the ReporRequest initialization
 At the first invalid column detected this method raises Exception.
 If all column values are ok, this method returns true
 Valid columns are validated against COLUMNS constant

 Author:: jlopezn@neonline.cl

 valid_columns - Hash with the valid names and values for columns
 columns - Hash with the columns specified in the initialization

 Returns:: true if all columns are ok
 Raises:: Exception at the first invalid column detected