How to do a sync SQL query in node.js [duplicate]

Question

Possible Duplicate:
Synchronous database queries with Node.js

Usually, we execute a SQL query and get the result in a callback. like this:

sqlExec('SELECT COL FROM TBL;', function (err, results, fields) {
    doSomething(results);
});

But if we need to do more complicated job with the SQL results, the code will be more uglier, like this:

var tmp = '';
sqlExec('SELECT COL1 FROM TBL1;', function (err, results, fields) {
    tmp = doSomething(results);
    sqlExec('SELECT COL2 FROM TBL2 WHERE CONDITION2 = ' + tmp +  ';', function (err, results, fields) {
        tmp = doSomething2(results);
        sqlExec('SELECT COL3 FROM TBL3 WHERE CONDITION3 = ' + tmp  + ';', function (err, results, fields) {
            ....
        });
    });
});

Do we have a idea to make it sync? like this:

var tmp = '', result = ''; 
result = sqlExec('SELECT COL1 FROM TBL1;');
tmp = doSomething(result);
sqlExec('SELECT COL2 FROM TBL2 WHERE CONDITION2 = ' + tmp  + ';');
tmp = doSomething(result);
sqlExec('SELECT COL3 FROM TBL3 WHERE CONDITION3 = ' + tmp  + ';');
...

Thanks, Gcaufy

It looks like the main thing that you're struggling with is chaining the async requests to be a little more manageable without all the nesting, right? — jcolebrand
– jcolebrand, Commented Aug 6, 2012 at 17:49
yes, if we can do these requests without nesting, that should be better. — Gcaufy
– Gcaufy, Commented Aug 7, 2012 at 5:22

Roest · Accepted Answer · 2012-08-06 17:59:56Z

1

A nice pattern is described here http://stella.laurenzo.org/2011/03/bulletproof-node-js-coding/ paragraph 2, with your example it would be something like this:

sqlExec('SELECT COL1 FROM TBL1;', function (err, results, fields) {
    var tmp = doSomething(results);
    nextStep( tmp );
}

function nextStep( tmp ) {
    sqlExec('SELECT COL2 FROM TBL2 WHERE CONDITION2 = ' + tmp +  ';', function (err, results, fields) {
    var othertmp = doSomething2(results);
    nextNextStep( othertmp );
    }
}

function nextNextStep( tmp ) {
    sqlExec('SELECT COL3 FROM TBL3 WHERE CONDITION3 = ' + tmp  + ';', function (err, results, fields) {
        ....
 }

now it almost looks like your desired result

answered Aug 6, 2012 at 17:59

Roest

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1 Comment

jcolebrand Over a year ago

Even with these functions you should be doing callbacks for the other functions

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