将回调函数传递给 mongoose 聚合函数

Question

我正在形成要在 aggregate() 中执行的查询，如下所示：

query.$project = {};
query.$project.created_at = '$created_at';
query.$project.month = {};
query.$project.month.$month = currentMonth;
query.$match = {};
query.$match.month = currentMonth.getMonth() + 1;
query.$limit = 5;
query.$sort = {};
query.$sort.created_at = -1;
query.callback = function(err, result){
    // do something
};
console.dir(query);

但是当我执行以下操作时：

DataTable.aggregate(query);

我明白了：

Error: Arguments must be aggregate pipeline operators
    at Aggregate.append (C:\myproject\node_modules\mongoose\lib\aggregate.js:87:11)
    at new Aggregate (C:\myproject\node_modules\mongoose\lib\aggregate.js:47:17)
    at Function.aggregate (C:\myproject\node_modules\mongoose\lib\model.js:1889:17)
    at C:\myproject\app\routes.js:179:23
    at C:\myproject\node_modules\async\lib\async.js:570:21
    at C:\myproject\node_modules\async\lib\async.js:249:17
    at C:\myproject\node_modules\async\lib\async.js:125:13

我现在有两个问题：

• 有没有更好的方法来形成这个查询。
• 以及如何在这里指定回调函数。

编辑

我将上面的代码修改如下：

query.$project = {};
query.$project.created_at = '$created_at';
query.$project.month = {};
query.$project.month.$month = currentMonth;
query.$match = {};
query.$match.month = currentMonth.getMonth() + 1;
query.$limit = 5;
query.$sort = {};
query.$sort.created_at = -1;

但是当我执行以下操作时：

DataTable.aggregate(query, function(err, result){
    // do something
});

Answer 1

引用Mongoose's documentation for aggregate，

参数：

1. [...] <Object, Array>聚合管道运算符或运算符数组

2. [callback] <Function>

期待你通过

1. 聚合管道运算符数组

   DataTable.aggregate([{
       $project: {
           created_at: '$created_at',
           month: {
               $month: currentMonth
           }
       }
   }, {
       $match: {
           month: currentMonth.getMonth() + 1
       }
   }, {
       $limit: 5
   }, {
       $sort: {
           created_at: -1
       }
   }], function(err, result) {
   
   });
   

2. 或多个聚合管道运算符作为单独的参数传递

   DataTable.aggregate({
       $project: {
           created_at: '$created_at',
           month: {
               $month: currentMonth
           }
       }
   }, {
       $match: {
           month: currentMonth.getMonth() + 1
       }
   }, {
       $limit: 5
   }, {
       $sort: {
           created_at: -1
       }
   }, function(err, result) {
   
   });
   

我更喜欢管道构建器的方式，

DataTable.aggregate().project({
    created_at: '$created_at',
    month: {
        $month: currentMonth
    }
}).match({
    month: currentMonth.getMonth() + 1
}).limit(5).sort({
    created_at: -1
}).exec(function(err, result) {

});

编辑：如果您喜欢单独准备单个项目，那么您可以使用数组对象，像这样

var query = [];

query.push({
    $project: {
        created_at: '$created_at',
        month: {
            $month: currentMonth
        }
    }
});

query.push({
    $match: {
        month: currentMonth.getMonth() + 1
    }
});

query.push({
    $limit: 5
});

query.push({
    $sort: {
        created_at: -1
    }
});

DataTable.aggregate(query, function(err, result) {

});

或者使用管道生成器，

var aggregator = DataTable.aggregate();
...
aggregator = aggregator.project({...});
...
aggregator = aggregator.match({...});
...
aggregator = aggregator.limit(...);
...
aggregator = aggregator.sort(...);
...
aggregator.exec(function(err, result) {

});