Node JS Synchronous database call

Question

I have a problem using Node JS when making synchronous calls.. Here's my problem:

I have the following code:

async.doWhilst(function(callback) {
    //some code
    callback();
}, function() {
    //make a database call and based on the results I should 
    //return true to continue looping or false to stop here
}, function(err) {
   //do some things when the loop finishes
})

The problem is when calling the database it is asynchronous call and the loop continues before even returning the proper value.

Thank you alot for your comments, I have solved the problem by move the database call to the loop code like this:

var results = []
async.doWhilst(function(callback) {
    //some code
    sequelize.query('some query').success(function(result) {
        results = result;
        callback();
    });
}, function() {
    //use the results variable that is fetched from the database
    //return true to continue looping or false to stop here
}, function(err) {
   //do some things when the loop finishes
})

The test function should be synchronous, it would be really, really, really bad to try to introduce async code and some kind of wait loop in it — Jan Aagaard Meier
– Jan Aagaard Meier, Commented Nov 10, 2014 at 8:33
I tried to make it synchronous but I can't figure out how, the problem is the database call depends on a variable changes in the loop code — Sami
– Sami, Commented Nov 10, 2014 at 8:39
You can't make an async operation behave synchronously. You just can't. It doesn't have the same timing as a synchronous operation and cannot be made to. — jfriend00
– jfriend00, Commented Nov 10, 2014 at 8:45
Thank you a lot @JanAagaardMeier your comment gave me a hint to move the database call to the loop code.. I will right an answer to what I have done. — Sami
– Sami, Commented Nov 10, 2014 at 8:46

Josh Lankford · Accepted Answer · 2014-11-10 08:34:56Z

1

You can have Sequelize return once the data has actually returned using this method:

return sequelize
  .query("Database query here")
  .success(function(result) {
      //Do something with result here
      else {
          //Return error
      }
  });

answered Nov 10, 2014 at 8:34

Josh Lankford

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Comments

matteo · Accepted Answer · 2014-11-10 08:31:14Z

0

Hope the following can help:

(function iterate() {
   executeDatabaseCall(..., function(e,r) {
      if (...conditions to continue looping are verified...)
         iterate();
      else
         ...manage the end of loop...
   });
})();

answered Nov 10, 2014 at 8:31

matteo

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mfrachet · Accepted Answer · 2014-11-10 08:51:00Z

0

If you really want to use sync call, you can use this library :

https://github.com/luciotato/waitfor

It'll permit you to make sync call using :

var syncDataReceived = wait.forMethod(collection,'insert',{data:toinsert});

answered Nov 10, 2014 at 8:51

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mfrachet

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Sami · Accepted Answer · 2014-11-10 09:13:47Z

0

I have solved the problem by move the database call to the loop code like this:

var results = []
async.doWhilst(function(callback) {
    //some code
    sequelize.query('some query').success(function(result) {
        results = result;
        callback();
    });
}, function() {
    //use the results variable that is fetched from the database
    //return true to continue looping or false to stop here
}, function(err) {
   //do some things when the loop finishes
})

answered Nov 10, 2014 at 9:13

Sami

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1 Comment

lin Over a year ago

This is not a synchronous Database call.

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