cradle

A high-level, caching, CouchDB client for Node.js

introduction

Cradle is an asynchronous javascript client for CouchDB. It is somewhat higher-level than most other CouchDB clients, requiring a little less knowledge of CouchDB's REST API. Cradle also has built-in write-through caching, giving you an extra level of speed, and making document updates and deletion easier. Cradle was built from the love of CouchDB and Node.js, and tries to make the most out of this wonderful marriage of technologies.

philosophy

The key concept here is the common ground shared by CouchDB and Node.js, that is, javascript. The other important aspect of this marriage is the asynchronous behaviors of both these technologies. Cradle tries to make use of these symmetries, whenever it can. Cradle's API, although closely knit with CouchDB's, isn't overly so. Whenever the API can be abstracted in a friendlier, simpler way, that's the route it takes. So even though a large part of the Cradle <--> CouchDB mappings are one to one, some Cradle functions, such as save(), can perform more than one operation, depending on how they are used.

synopsis

var cradle = require('cradle');
var db = new(cradle.Connection)().database('starwars');

db.get('vador', function (err, doc) {
    doc.name; // 'Darth Vador'
    assert.equal(doc.force, 'dark');
});

db.save('skywalker', {
    force: 'light',
    name: 'Luke Skywalker'
}, function (err, res) {
    if (err) {
        // Handle error
    } else {
        // Handle success
    }
});

installation

$ npm install cradle

API

Cradle's API builds right on top of Node's asynch API. Every asynch method takes a callback as its last argument. The return value is an event.EventEmitter, so listeners can also be optionally added.

Opening a connection

new(cradle.Connection)('http://living-room.couch', 5984, {
    cache: true,
    raw: false
});

Defaults to 127.0.0.1:5984

Note that you can also use cradle.setup to set a global configuration:

cradle.setup({host: 'http://living-room.couch',
              options: {cache: true, raw: false}});
var c = new(cradle.Connection),
   cc = new(cradle.Connection)('173.45.66.92');

creating a database

var db = c.database('starwars');
db.create();

You can check if a database exists with the exists() method.

fetching a document (GET)

db.get('vador', function (err, doc) {
    sys.puts(doc);
});

If you want to get a specific revision for that document, you can pass it as the 2nd parameter to get().

Cradle is also able to fetch multiple documents if you have a list of ids, just pass an array to get:

db.get(['luke', 'vador'], function (err, doc) { ... });

Querying a view

db.view('characters/all', function (err, res) {
    res.forEach(function (row) {
        sys.puts(row.name + " is on the " +
                 row.force + " side of the force.");
    });
});

creating/updating documents

In general, document creation is done with the save() method, while updating is done with merge().

creating with an id (PUT)

db.save('vador', {
    name: 'darth', force: 'dark'
}, function (err, res) {
    // Handle response
});

creating without an id (POST)

db.save({
    force: 'dark', name: 'Darth'
}, function (err, res) {
    // Handle response
});

updating an existing document with the revision

db.save('luke', '1-94B6F82', {
    force: 'dark', name: 'Luke'
}, function (err, res) {
    // Handle response
});

Note that when saving a document this way, CouchDB overwrites the existing document with the new one. If you want to update only certain fields of the document, you have to fetch it first (with get), make your changes, then resave the modified document with the above method.

If you only want to update one or more attributes, and leave the others untouched, you can use the merge() method:

db.merge('luke', {jedi: true}, function (err, res) {
    // Luke is now a jedi,
    // but remains on the dark side of the force.
});

Note that we didn't pass a _rev, this only works because we previously saved a full version of 'luke', and the cache option is enabled.

bulk insertion

If you want to insert more than one document at a time, for performance reasons, you can pass an array to save():

db.save([
    {name: 'Yoda'},
    {name: 'Han Solo'},
    {name: 'Leia'}
], function (err, res) {
    // Handle response
});

creating views

Here we create a design document named 'characters', with two views: 'all' and 'darkside'.

db.save('_design/characters', {
    all: {
        map: function (doc) {
            if (doc.name) emit(doc.name, doc);
        }
    },
    darkside: {
        map: function (doc) {
            if (doc.name && doc.force == 'dark') {
                emit(null, doc);
            }
        }
    }
});

These views can later be queried with db.view('characters/all'), for example.

removing documents (DELETE)

To remove a document, you call the remove() method, passing the latest document revision.

db.remove('luke', '1-94B6F82', function (err, res) {
    // Handle response
});

If remove is called without a revision, and the document was recently fetched from the database, it will attempt to use the cached document's revision, providing caching is enabled.

Changes API

For a one-time _changes query, simply call db.changes with a callback:

db.changes(function (list) {
    list.forEach(function (change) { console.log(change) });    
});

Or if you want to see changes since a specific sequence number:

db.changes({ since: 42 }, function (list) {
    ...
});

The callback will receive the list of changes as an Array. If you want to include the affected documents, simply pass include_docs: true in the options.

Streaming

You can also stream changes, by calling db.changes without the callback:

db.changes({ since: 42 }).on('response', function (res) {
    res.on('data', function (change) {
        console.log(change);
    });
    res.on('end', function () { ... });
});

In this case, it returns an EventEmitter, which behaves very similarly to node's Stream API.

Other API methods

CouchDB Server level

new(cradle.Connection)().*

• databases(): Get list of databases
• config(): Get server config
• info(): Get server information
• stats(): Statistics overview
• activeTasks(): Get list of currently active tasks
• uuids(count): Get count list of UUIDs

database level

new(cradle.Connection)().database('starwars').*

• info(): Database information
• all(): Get all documents
• allBySeq(): Get all documents by sequence
• compact(): Compact database
• viewCleanup(): Cleanup old view data