code: function (graph, opts, params) {
      var self = this;
      var savedNodes = graph.allNodes.filter(function(node) {
        return node.props[self.db.options.id] != null 
            && !(node.model.uniqueness && node.model.uniqueness.returnOld);
      });
  
      if (!savedNodes.length) return '';
  
      var statements = savedNodes.map(function(node) {
        params[node.name + 'id'] = getId(self.db, node.props);
        return node.name + '=node({' + node.name + 'id})';
      });
  
      return 'START ' + statements.join(',');
    }
docs: get the START statement of a write query this will start with all the pre-existing nodes