how to return data from client.query cb event to function?

[Mathiu]

Hello everyone, i have started my journey with nodejs a couple weeks ago and i have a problem, dont know what exacly is it, issue or what, anyways, I have a function in my lib file getUserData to retrive user data from mysql:

lib.getUserData = function(userId) {
var resultUser = {};
mysqlc.query("SELECT * FROM za_users WHERE id = ?", [userId],
function(err, results) {
if (err) {
throw err;
}
resultUser = results;
});
return resultUser;
}

and when i call that function from my main file i always gets an empty object. I tried a lot of ways but none of them works :/
I know that i can put client.query to my main file without function but i want to have a clean code.

I tried return reuslts to this.variable, i've created function to retrive last results, and i spend tree days on this, and i'am despred. So i really be greatful for any advice here.

[Mathiu]

OK, i'am sorry i didnt know about assynchronous calls, but how can i use this results data? Is one and only way is to use some function inside function(err, results) { } and then execute some instructions?

Sorry for my ignorance, i'am kind of newbie in js, and my english, i'am from Poland.

[davide-scalzo]

I had the same problem, but then I read more in detail the documentation.
that's what I understood:
The client.query returns a Query object that has some events, row, field, end and so on... so if you attach an event listener like

sqlResult = sql.query("SELECT * FROM za_users WHERE id = ?", [userId]);
sqlResult.on('row', function(row) {
  //assuming we are routing a get request, let's publish our result on the browser
  res.write(row.name);
});

What I still need to understand is how to put all this data into a variable that I can manage through the JADE engine :S

[mscdex]

@davodesign84

If you want all of the results at once instead one row at a time, pass in a callback to query(), like so:

sql.query("SELECT * FROM za_users WHERE id = ?", [userId], function(err, rows) {
  // check if err is set first
  // then pass rows to your template
  // where rows is an array of the records returned from the server
  //   i.e.: rows[0].name, rows[0].foo; rows[1].name, rows[1].foo
});

[davide-scalzo]

That works but then we go back to the question that Mathiu was asking, so how do retrieve that array from the callback.

Which is also not a good idea as ideally we should try to keep everything async as possible!
At least to my understanding..

[mscdex]

@davodesign84

In his case, you'd have to pass in a callback instead of using the return value of the function because the query is async:

lib.getUserData = function(userId, cb) {
  mysqlc.query("SELECT * FROM za_users WHERE id = ?", [userId], 
    function(err, results) { 
      if (err)
        return cb(err);
      cb(undefined, results);
  });
}

// Usage:
lib.getUserData(1337, function(err, results) {
  // use results in your template if !err
});

[Mathiu]

At first very thanks for replies guys.

Your code seems great, but i cant check it right now and i will be able
after this weekend, so ill post are they enough for me.

2011/8/12 mscdex <
reply@reply.github.com>

@davodesign84

In his case, you'd have to pass in a callback instead of using the return
value of the function because the query is async:

lib.getUserData = function(userId, cb) {
 mysqlc.query("SELECT * FROM za_users WHERE id = ?", [userId],
   function(err, results) {
     if (err)
       return cb(err);
     cb(undefined, results);
 });
}

// Usage:
lib.getUserData(1337, function(err, results) {
 // use results in your template if !err
});

Reply to this email directly or view it on GitHub:
#81 (comment)

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Dirt Arts CEO

[davide-scalzo]

cool I'll try that as well, seems easier than having a stream of data (guess that for that I need socket.io) and should be perfect for most application, thanks!

[bslayton]

@mscdex

I added a callback function, and I can do console.write(results) and it works. However I cannot do response.write the results.I am passing the response and request vars to my callback but it doesn't write to my screen. If I do console.write(response) it will give me the same data as if I were outside of my callback function.

Any idea on what to do?

[mscdex]

@bslayton can you provide a gist of the code?

[arnoprinz]

I'm working on that interface-problem since i'm working with the mysql-database. The target is an web-application without mvc or something with magic. I'm using jade as template-engine, because i can use dynamic node-code and jquery + jquery-ui for dynamic html.

First of all you must have some rooting to handle the GET form web-client (i use meryl.js).
Jade has an option called locals to inject or interpolate the rendered jade-file.

it could be every-request-response-function with callback:

 .handle('GET /mypartial', function (req, resp) {
     mysqlc.query("SELECT * FROM za_users ", 

       // here begins the callback-function body, witch is drilled down
       // in the depths of the query

       function(err, rows) { 
         if (err) return cb(err);

         // this variables passes the result to jade 
         var elements= { datarows: rows }  
         var options = {locals:{elements:elements}};

         jade.renderFile(__dirname + '/forms/partial.jade', options, function(err, html){
           if (err) throw err;
              //console.log(html)
              resp.write(html);
              resp.end();         
         }); //render 



   });

 })



 partial.jade
 ============

 the code injection should report the transfered rows in the node-console

  - console.log('\n>>>> jade-partial <<<<\n') 
  - console.log('test locals, elements: ', elements)

[mscdex]

What if you take out the jade rendering and try simply doing something like:

 .handle('GET /mypartial', function (req, resp) {
     mysqlc.query("SELECT * FROM za_users ", 

       // here begins the callback-function body, witch is drilled down
       // in the depths of the query

       function(err, rows) { 
         if (err) return cb(err);
         resp.end(JSON.stringify(rows));
   });
 })

If that works, then maybe it's jade-related and nothing to do with node-mysql?

[bslayton]

I figured out my problem. I have created my own mini framework for handling models and controllers. No views since this is housing an API. I couldn't do response.write in my controller when response.end() was in my main app.js file after I call my controller for some reason. It's like it was skipping it or something. No biggy, I just had to put my response.end() in my database callback in the controller.

[felixge]

Closing this, seems resolved. Thanks @mscdex for providing your input.