Sails JS - Nested .query method doesn't run sequence

Question

I beginner in Sails JS. I try to make multiple .query("SELECT ... "). I have a problem when looks like it not run sequence. I will explain my problem, look to My snippet code :

var isSuccess = true;
for(var loc = 0 ; loc < decode.length ; loc++){
    Location.query('SELECT * FROM abc', function (err, res){
      if (err) {
        isSuccess = false;
        return res.json(200, {
          data: {

          },
          status: {
            id: 0,
            message: err.message
          }
        });
      } else {
        var validate = res.rows;
        sails.log(validate);

      secondQuery.query('SELECT * FROM def', function (err, seconResult) {
        if (err) {
          isSuccess = false;
          sails.log("Update is Success : "+isSuccess);
          return res.json(200, {
            data: {

            },
            status: {
              id: 0,
              message: err.message
            }
          });
        } else {


        }
      });
      }
    });

    if(isSuccess){
      return res.json(200, {
        data: {

        },
        status: {
          id: 1,
          message: "Successful",
          isSuccess: isSuccess
        }
      });
    }
  }

When i request the API via POST method and the result is :

On Console Node JS Server :

Update is Success : false So it means the request is failed and must be return status = 0 in postman

But in the Postman, it show :

  data: {

        },
        status: {
          id: 1,
          message: "Successful",
          isSuccess: true
        }

My Question :

Can anyone help me to explain why and how to make it a sequence process, not like "multi thread" ? (In my case, i need to use RAW query cause i will face with really complex query)

Thank you.

Needing to do queries in a for-loop will always feel "multi-threaded", there is no avoiding that complication. Can you be more specific about the nature of your queries? You may be able to combine then into one, or if not, there may be a way to trigger some code to run when they are all complete. — arbuthnott, Dec 20 '17 at 12:32
Combine into one? Can you explain more how to combine into one ? Thank you. — Mr. Mike, Dec 21 '17 at 01:44
Can you give a more specific example than `SELECT * FROM abc`? — arbuthnott, Dec 21 '17 at 10:50

score 1 · Accepted Answer · answered Jan 15 '18 at 11:00

1

A for loop is synchronous while Location.query() method is not. So if you want to do it in sequence, you'll have to use Bluebird Promise.

Example (not tested) :

const Bluebird = require('bluebird');

const promises = [];
for(let loc = 0 ; loc < decode.length ; loc++) {
  promises.push(Location.query('SELECT ...'));
}

Bluebird.each(promises, (result) => res.json(200, {/* your payload data */}))
        .catch((err) => res.json(200, {/* your error data */}));

NB : Be careful when you use res variable in your callbacks when you use it in Sails controllers.

answered Jan 15 '18 at 11:00

Martial

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How about nested loop? can you give example for nested loop with promise? – Mr. Mike Jan 16 '18 at 15:55
@Michael Can you provide an example of the nested loop you want to use so that I can show you how to change your code with promises ? – Martial Jan 16 '18 at 16:06

Sails JS - Nested .query method doesn't run sequence

1 Answers1