node.js - 如何在 Mongoose 中将一个查询的对象用于嵌套查询

Question

我是 MongoDb 和 NodeJs 的新手，我在 NodeJS 中使用 Mongoose，但我面临一个问题，我将第一个查询的结果对象使用到嵌套查询中，但第一个查询对象未定义。请给我任何建议。谢谢。

LuckyLunch.find(criteria, function (err, lunches) {   // First Query
   if (err) 
       return;
   var allLunches = lunches;   // Accurate result here
   for (var i = 0; i < allLunches.length; i++)
       {
         if (typeof allLunches[i].luckyMatch != 'undefined') {
              var usernames = [];
              Match.findOne(criteria2, function (err, singleMatch) {   // Second Query
                if (singleMatch != null) {
                     var userids = [];
                   for (var k = 0; k < singleMatch.participants.length; k++)
                   {
                      userids.push(ObjectId(singleMatch.participants[k]));
                   }
                      User.find(criteria, function (err, getusers) {  // Third Query
                      for (var j = 0; j < getusers.length; j++)
                          usernames.push(getusers[j].name);

                      allLunches[i].luckyUsers = usernames;  // allLunches[i] is undefined here.

                   });
                 }
              });
            }
          } 
      });

Answer 1

试试这个，

 var getData = function(callback) {
     LuckyLunch.find(criteria, function (err, lunches) {   // First Query
      if (err) {
         callback(err); 
         return;
      }        
      var len =   lunches.length; // try to use lenches only, Accurate result here
      for (var i = 0; i < len; i++)
       {
        (function(i) { 
         if (typeof lunches[i].luckyMatch != 'undefined') {
          var usernames = [];
          Match.findOne(criteria2, function (err, singleMatch) {   // Second Query
            if (singleMatch) {
                 var userids = [];
               for (var k = 0; k < singleMatch.participants.length; k++)
               {
                  userids.push(ObjectId(singleMatch.participants[k]));
               }
                  User.find(criteria, function (err, getusers) {  // Third Query
                  for (var j = 0; j < getusers.length; j++)
                      usernames.push(getusers[j].name);

                  lunches[i].luckyUsers = usernames;  // allLunches[i] is undefined here.

               });
             }
          });
        }
        })(i);
      }

      callback(null, "put here need data to return"); //this must be end of the ur loop
  });

 }

 getData(function(err, result){

   if(err)
     console.log(err);
     else
     console.log(result); 
 });