Question

我有一组带有express / mongoose的嵌套查询，非常类似：

app.get(..., function(...) {

   Schema1.query(..., function(..., res1) {

      for ( var key in res1 ) {
           Schema2.query(..., function(..., res2) {
             data[key].appendedAttribute = res2.somedata;
            });
      }

      res.render(..., data);
   });

}）;

哪个不起作用，也就是说，additionalAttribute永远不会附加到数据集。我做错了什么？

Answer 1

使用after

app.get(..., function(...) {
    Schema1.query(..., function(..., res1) {
        var cb = after(Object.keys(res1).length, function () {
            res.render(..., data);    
        });

        for (var key in res1) {
            Schema2.query(..., function(..., res2) {
                data[key].appendedAttribute = res2.somedata;
                cb();
            });
        }
    });
});

基本上，您必须在第二个查询完成后才启动res.render调用。

Answer 2

使用Step：

app.get(..., function(...) {
  var data;
  Step(
    function first_query() {
      Schema1.query(...,this);
    },
    function multiple_queries(err, res1) {
      for (var key in res1) {
        Schema2.query(..., function(..., res2) {
          data[key].appendedAttribute = res2.somedata;
          this.parallel(); // make sure callback gets executed only after all the queries are executed
        });
      }     
    },
    function render() {
      res.render(..., data);
    }
  );
});

Node JS，express，Mongoose，嵌套查询

2 个答案: