I am trying to developpe an API with NodeJs which accepts an object containing multiple queries to mongdb and answers an object with the different results (in fact Json).
I use express and my code is :
var nb_query=0;
var results;
//api
app.get("/api/:p",api);
function api(req, res) {
var jsonq=decodeURIComponent(req.params.p);
//console.log(jsonq);
var queries=JSON.parse(jsonq);
nb_query=Object.keys(queries).length;
results={};
for(var nq in queries) { // for each query
do_find_query(nq,queries[nq], function() {
//todo : managing head
res.end(JSON.stringify(results));
}
);
}
} // end of api function
function do_find_query (name_query,query,callback) {
var collection=fdb.collection(query.collection);
collection.find(query.find,query.fields,query.options).toArray(function(err,docs) {
if(err) throw err;
results[name_query]=docs;
nb_query--;
if(nb_query==0)
callback();
}
);
}
As you see, I use global vars to store the results and the counter nb_query. And I ask myself if it is a problem or not (now no because I am alone on the server, but when we will be thousands of billions? :-) ).
As I understand Node, there is only one thread and I think Node will finalize a started job unless he encoutered an io access. In this case, he stacks the io with the callback, and begins to answer to a new request.
If this is correct, I think that Node could answer to 2 or more different calls to my api (which need mongo calls) and so store different values in global vars which is shared (there's only one thread).
If this is right, I would also know what is the best way to change it. I have the idea of declaring results and nb_query in api function and pass it to do_find_query, but nb_query isn't an object and is so not changed correctly.
I know I can put nb_query in an object to pass it 'by reference', but I want to know first if it is necessary and if it is a good way or if there is a better one.
Thanks for your help !
Doom.
EDIT : I have change my code and it seems to work without global vars and without async library (which is for me using a hammer to swat a fly)
//api
app.get("/api/:p",api);
function api(req, res) {
var jsonq=decodeURIComponent(req.params.p);
//console.log(jsonq);
var queries=JSON.parse(jsonq);
var query_names=Object.keys(queries);
var results={};
var query_left=query_names.length;
query_names.map( function(query_name) {
var query=queries[query_name];
var collection=fdb.collection(query.collection);
collection.find(query.find,query.fields,query.options).toArray(function(err,docs) {
if(err) throw err; //todo : handle errors in a better way
results[query_name]=docs;
if(--query_left==0)
res.json(results);
}
);
}
);
}
But I still do not know if this is necessary to do or not. (I think so but I am new in Node so ...)
Thanks to mscdex as his answer make me known res.json() and help me understand scope of variable.
Instead of using globals, try this (uses the async module):
var async = require('async');
// ...
app.get('/api/:p', api);
function api(req, res) {
var jsonq = decodeURIComponent(req.params.p),
queries = JSON.parse(jsonq),
keys = Object.keys(queries),
queriesLeft = keys.length,
results = {};
async.each(keys, function(name, cb) {
var query = queries[name],
collection = fdb.collection(query.collection);
collection.find(query.find, query.fields, query.options)
.toArray(function(err, docs) {
if (err) return cb(err);
results[name] = docs;
cb();
}
);
}, function(err) {
if (err) throw err; // TODO: handle better
res.json(results);
});
} // end of api function