Pass-Thru Node.js and CouchDB

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Up tonight, I try to get started with a simple node.js / CouchDB application. I am a big fan of CouchDB with node.js because CouchDB speaks HTTP natively. There is no need for middleware or data drivers with CouchDB—I can just make HTTP requests and process the response or send it along to the client.

I already have the latest node.js installed and a CouchDB server running.

My first step is to create a simple express.js application to play with:

➜  repos  express calendar   
   create : calendar
   create : calendar/package.json
   create : calendar/app.js
   create : calendar/public/stylesheets
   create : calendar/public/stylesheets/style.css
   create : calendar/public/javascripts
   create : calendar/public/images
   create : calendar/views
   create : calendar/views/layout.jade
   create : calendar/views/index.jade

In the new "calendar" app directory, I need to install the express and jade packages from npm:

➜  calendar git:(master) ✗ npm install express jade
jade@0.14.2 ./node_modules/jade 
express-unstable@2.4.3 ./node_modules/express
├── mime@1.2.2
├── connect@1.6.0
└── qs@0.3.1

My next step is to use the Futon admin interface to create a database. I fancy a calendar app, so I name my database accordingly:

Next, I create a calendar event:

And an event for tomorrow:

To allow my simple express.js app to pass those events back to the browser, I need to establish a route for all events. In that route, I access the special _all_docs resource in CouchDB to pull back all records in the calendar DB (I prolly would not do that in a larger DB). Once the Couch DB response comes back, I write the data back to the browser:

app.get('/events', function(req, res){
  var options = {
    host: 'localhost',
    port: 5984,
    path: '/calendar/_all_docs'
  };

  http.get(options, function(couch_response) {
    console.log("Got response: %s %s:%d%s", couch_response.statusCode, options.host, options.port, options.path);

    res.contentType('json');

    // Send all couch data to the client
    couch_response.on('data', function (chunk) {
      res.write(chunk);
    });

    // When couch is done, so is this request
    couch_response.on('end', function (chunk) {
      res.end();
    });
  }).on('error', function(e) {
    console.log("Got error: " + e.message);
  });
});

That's a bit of work establishing 'data' and 'end' listeners. Fortunately, node has an answer for this case in the pipe method for all stream objects:

  http.get(options, function(couch_response) {
    console.log("Got response: %s %s:%d%s", couch_response.statusCode, options.host, options.port, options.path);

    couch_response.pipe(res)
  })

Any events emitted by couch_response will be sent to the original Response object. The result of calling accessing the /events resource is:

As can be seen in the screen shot, the actual event data is not being returned—just IDs and other metadata. To get the full event, I can create another express.js route with a similar callback:

app.get('/events/:id', function(req, res){
  var options = {
    host: 'localhost',
    port: 5984,
    path: '/calendar/' + req.params.id
  };

  http.get(options, function(couch_response) {
    console.log("Got response: %s %s:%d%s", couch_response.statusCode, options.host, options.port, options.path);

    couch_response.pipe(res);
  }).on('error', function(e) {
    console.log("Got error: " + e.message);
  });
});

This route makes use of some nifty parameter assignments in express.js. Named parameters in the route (the :id in /events/:id) are made available in the request params object (e.g. req.params.id). That bit of coolness aside, this is nearly identical to the all-events route from above.


That is all well and good, but I do not think that I want my client making dozens of calls to this resource for each event on a particular calendar. Instead, I go back into my /events route and add include_docs=true to the URL. This includes the documents (which are relatively small) along with the meta data:

Cool beans. That is a good stopping point for tonight. Tomorrow I will hook those into jQuery Ajax calls to build a month-view calendar. And then the fun begins with a backbone.js equivalent.

Day #124