mongoose count()方法查询的结果如何以数组返回？

Question

我想用mongoose的count方法查询stations集合里各个部门的数量，push进一个数组然后返回给Echarts，可是响应的却是空的数组，请教各位大神应该怎么解决？

router.get('/chart', function (req, res, next) {
  let depts = ['部门1', '部门2', '部门3', '部门4', '部门5',
    '部门6', '部门7', '部门8'];
  let department = [];
  for(let x in depts){
    stations.count({"dept": depts[x]}).exec(function (err, counts) {
      department.push(counts);
    });
  }
  res.json(department);
});

Answer 1

let department = [];
  let asynQuery = () => {
    return new Promise( (resolve, reject) => {
      stations.aggregate([{$group: {_id: "$dept", count: {$sum: 1}}}]).exec(function (err, doc) {
        department.push(doc);
        resolve(department);
      });
    });
  }
  asynQuery().then(department=>{
    res.json(department)
  });

原来是异步的问题，通过Promise解决了

Answer 2

用Aggregation吧，很好实现。你这样得查n次，用aggregation只用一次查出所有。以下是shell示例（并不太熟悉mongoose...）

let department = []
db.stations.aggregate([
    {$group: {_id: "$dept", count: {$sum: 1}}}
]).forEach(doc => {
    department.push(doc.count);
});