如何在1个get调用nodejs中运行多个查询

Question

app.get('/projects/:company_id', function(req, res){
    var company_id = req.params.company_id;

    //query1
    db.projects.count({"company_id": company_id },function(err, doc){   
        res.json(doc);
    });
    //query2
    db.projects.find({"company_id": company_id },function(err, doc){    
        res.json(return_data);
    });
});

Basically I want these two queries to run in parallel and then send the output to front end. I am not sure how to achieve that, guys help!. Also is there an easy way to separate these two results in front end. I am using angular js.

Answer 1

You could run them side by side and send the data after both run. Check async library which is one of many libraries to do such operations easily.

var async = require("async");
async.parallel({
    one: function(callback) {
        db.projects.count({"company_id": company_id },function(err, doc){   
            callback(null, doc)
        });
    },
    two: function(callback) {
        db.projects.find({"company_id": company_id },function(err, doc){    
            callback(null, doc);
        });
    }
}, function(err, results) {
    var payload = {
        count : results.one,
        data: results.two
    }
    res.json(payload);
});

Answer 2

If you want to do it without any additional library, you could do something similar to this:

app.get('/projects/:company_id', function(req, res) {
  // Create an object resembling your final response,
  // but replace the values with a promise.
  var futureData = {
    count: new Promise(function(resolve, reject) {
      db.projects.count({'company_id': company_id}, function(err, doc) {
        if (err) {
          return reject(err);
        }
        return resolve(doc);
      });
    }),
    results: new Promise(function(resolve, reject) {
      db.projects.find({'company_id': company_id}, function(err, doc) {
        if (err) {
          return reject(err);
        }
        return resolve(doc);
      });
    }),
  };

  var keys = Object.keys(futureData);

  // Wait until all promises are resolved.
  Promise.all(
    keys.map(key => futureData[key])
  )
    // Get the response object.
    .then(function(values) {
      // Build an object from the results of the promises,
      // using the same key as in `futureData`.
      return values.reduce(function(data, value, i) {
        var key = keys[i];
        data[key] = value;
        return data;
      }, {});
    })
    .then(function(data) {
      // Send final data.
      res.json(data);
    })
    .catch(function(err) {
      // TODO: Handle error.
    });
});

Answer 3

You want to use Promise.all() to wait both queries are finished.

Of course you need promises inside it, so we wrap each of the two function of yours in a promise , which is fulfilled when the callback is called.

If one of the two queries fail, then also Promise.all() fails and we send back to the client the error.

To separate data in the reply I split the data in two fields, count and find . In this way you can read them easily from angularjs and use them as you wish

app.get('/projects/:company_id', function(req, res){
    var company_id = req.params.company_id;

    Promise.all(
      new Promise(resolve, reject) {
        db.projects.count({"company_id": company_id },function(err, doc){   
          if (err) return reject(err);
          resolve(doc);
        });
      },
      new Promise(resolve, reject) {
        db.projects.find({"company_id": company_id },function(err, doc){   
          if (err) return reject(err);
          resolve(doc);
        });
      }
    )
    .then(data) {
      res.json({
        "count": data[0],
        "find": data[1]
      });
    }
    .catch(error) {
      res.json({
        "error": error
      });
    }
});

If you can't use Promises 'cause you're using node.js 0.10.x, you can do something like this:

app.get('/projects/:company_id', function(req, res){
    var company_id = req.params.company_id;
    var reply = {
      find: -1,
      count: -1
    }
    var errorSent = false;

    function sendErr(e) {
      if (errorSent) return; // Do not send twice a reply
      res.json({"error": e});
      errorSent = 1;
    }

    function sendWhenReady() {
      if (reply.count !== -1 && reply.find !== -1) res.send(reply);
    }


    //query1
    db.projects.count({"company_id": company_id },function(err, doc){
        if (err) return sendError(err);
        reply.count = doc;   
        sendWhenReady();
    });
    //query2
    db.projects.find({"company_id": company_id },function(err, doc){ 
        if (err) return sendError(err);   
        reply.find = doc;   
        sendWhenReady();
    });
});