为什么await / async的结果未定义？

Question

I have a route like:

router.get("/my_resource", myController.getResult);

Then my controller is like:

getResult: async (req, res, next) => {
    try {
      const param = req.query.param;
      let response = {};
      if (param) {
        let [result1, result2] = await Promise.all([myModel.getResult1(param), myModel.getResult2(param)]);
        console.log(result1);
        console.log(result2);
      }
      res.send(response);
    } catch (e) { 
        next(e);
    }
  }

And my model (which is querying a mongodb) looks like:

getResult1: (param) => {
    new Promise((resolve, reject) => {
      MongoSchema1.findById(param, (error, result) => {
        if (error) return reject(error);
        resolve(result ? result : {});
      }).select("field1 field2");
    })
  }

getResult2: (param) => {
  new Promise((resolve, reject) => {
    MongoSchema2.findById(param, (error, result) => {
      if (error) return reject(error);
      resolve(result ? result : {});
    }).select("field1 field2");
  })
}

Here, when I try to console.log() in the model functions I can see that the result is not undefined . I get the correct result. However, I can see that the console.log() in the controller method gets executed before the console.log() in the model methods.

In the code above, I'm making the async calls in parallel with Promise.all() . However, even if I try to run one at a time, I still get my result to be undefined in the controller method. What am I doing wrong? Do I need import any module before I can await ? Thanks.

Answer 1

The problem is that your methods getResult1 and getResult2 do not return Promises objects.

Replace

  getResult1: (param) => {
    new Promise((resolve, reject) => {
      MongoSchema1.findById(param, (error, result) => {
        if (error) return reject(error);

        resolve(result ? result : {});
      }).select("field1 field2");
    })
  }

By

  getResult1: (param) => {
    return new Promise((resolve, reject) => {
      MongoSchema1.findById(param, (error, result) => {
        if (error) return reject(error);
        resolve(result ? result : {});
      }).select("field1 field2");
    });
  }

Or

  getResult1: param => new Promise((resolve, reject) => {
      MongoSchema1.findById(param, (error, result) => {
        if (error) return reject(error);

        resolve(result ? result : {});
      }).select("field1 field2"));
  }

Or

getResult1: async param => (await MongoSchema1.findById(param).select('field1 field2')) || {};

Or

getResult1: async param => (await MongoSchema1.findById(param, 'field1 field2')) || {};