If I have a database for node. node has different type. and I want to put some new node in to database. the same type node put the same list. if the node type is new.and create a new list . pseudo code : node = getnode(); for (nodetype in typelist) if(nodetype==node.type) push(node)into map[nodetype]. else create nodetype; map[newtype]=node; My method is not good .Give me some good tip or code sample.