Rendering multiple query results in NodeJS

Question

I want to render results from multiple queries to my template from NodeJS.

  connection.query("select * from table1",function(err,rows){

        if(!err) {

            var data1 = JSON.parse(JSON.stringify(rows));
            var data2 = fetchDataFromOtherTable(connection); //returns rows from another table
            console.log(data2); //prints undefined

            res.render('template-page',{data1:data1,data2:data2});
        }          
    });

This behaviour is obvious due to the async nature of javascript, and can be solved if I pass data1 to 'fetchDataFromOtherTable' and then render from that function :

 fetchDataFromOtherTable(res,data1,connection);

 /*In fetchDataFromOtherTable */

 data2 = JSON.parse(JSON.stringify(rows));
 res.render('template-page',{data1:data1,data2:data2});

However, for multiple queries, this technique will involve cumulative passing of returned 'rows' at each function call (Also, a lot of function redirects).

Is there a better way to achieve this?

Andrius · Accepted Answer · 2015-11-14 08:04:25Z

1

since NodeJS is asynchronous, you are kind of out of luck doing anything that would work in a large application without using additional modules.

The most popular modules to handle asynchronous calls are async and Q (promises).

Here's an example how to handle asynchronous operations with async:

async.auto({
    get_data: function(callback){
        console.log('in get_data');
        // async code to get some data
        callback(null, 'data', 'converted to array');
    },
    make_folder: function(callback){
        console.log('in make_folder');
        // async code to create a directory to store a file in
        // this is run at the same time as getting the data
        callback(null, 'folder');
    }]
}, function(err, results) {
    console.log('err = ', err);
    console.log('results = ', results);
});

It's fairly straightforward but you'll need to edit your function to run a callback function.

answered Nov 14, 2015 at 8:04

Andrius

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2 Comments

user2473779 Over a year ago

Thanks. I will give both of them a shot. As i see, these are essentially doing the same thing as redirects, but presented in a more organised way. Any thoughts on performance issues of async and promises though?

Andrius Over a year ago

There isn't any other solution if you want to do multiple async calls so I would not worry about it.

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