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I'm not sure if this is possible, I'm assuming something like this is. I've got a couple of JSON files containing a series of JSON objects, each with a unique ID. I'd like to be able to use a Node application to read these objects and return all of the objects with an ID greater than a parameter provided.

ie. /after/20 would return all of the JSON objects from the file whose ID is greater than 20.

These requests will be happening very frequently, by lots of different users. Therefore, I was wondering if there is a way to store or cache these files in some way which means they don't need to be repeatedly loaded. Therefore making the process both quicker and more efficient.

Luke Smith
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2 Answers2

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Here is a solution that will keep the whole dataset in memory. I am assuming you have at least node 0.5 (to require json), that the two json files are named json1 and json2 and I will use express because of its routing.

var express = require('express'),
http = require('http'),
json1 = require('./json1.json'),
json2 = require('./json2.json');

var app = express();

//Express config

app.configure(function(){
    app.set('port', 8080 );
    //...
    app.use(express.bodyParser());
    app.use(express.methodOverride());
    //Right before the router, add a middleware to expose your objects
    app.use(function(err, req, res, next){
        req.json1 = json1;
        req.json2 = json2;
        next();
    });
    app.use(app.router);
    //...
});

Finally, any router will have access to both json objects.

app.get('/after/:id', function(req, res){
    var objects = req.json1,
        id = req.params.id,
        result = objects.filter(function(obj){ return obj.id >= id; });
    res.json(200, result);
});
Community
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verybadalloc
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  • That's perfect, thanks. I'll have a dabble with this tomorrow morning. Looks ideal for my requirements. – Luke Smith Dec 23 '13 at 17:30
  • Worked perfectly. I had to make some minor alterations to fit the structure of the file but that was pretty much exactly what I needed. Thanks. – Luke Smith Dec 23 '13 at 20:07
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As far as I know, if you use node.js's "require" function to load a module (or JSON file, in your case), it is cached based on its filename.

See Node.JS API Doc about this.

I am using this technique in a project with many small files and they all get cached after their first load.

andy137
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