Neat Little Tricks by Anup Bishnoi

Exposing Firebase data as REST-like ORM store in Node.js

16 Oct 2014

A quick and dirty solution for the times when you want to connect to Firebase from the server, and not directly from the client browser, exposing Firebase data as simple asynchronous calls in Node.js.

Proposal

Just provide a Firebase URL and a few resource names to a utility module in order to get REST-like access to those resources (think tables) as simple asynchronous calls.

Example usage

Initialize the db (acting as ORM):

var db = require('./firebase-data')(
  'http://myblog.firebaseio.com',
  [ 'posts', 'comments' ]
);

Use db.create to create new objects of provided resource type:

db.create('posts', {
  title: 'Title',
  body: 'Body'
}, function (e, post) {
  var id = post.id;
  console.log('created with id', id);
});

Use db.read to read back the full list of objects of a particular resource type:

Important note: read does not fetch everything all over again from Firebase, it keeps a local copy and responds from that local copy, and keeps itself in sync with Firebase continuously (using Firebase realtime API).

So calling read again and again does not incur extra Firebase usage charges. Good thing. But it also means you will get an empty array if you try to read before a connection to Firebase has been established.

db.read('posts', function (e, posts) {
  // all posts have unique post.id
  console.log(posts);
});

Use db.update to update a particular object:

db.update('posts', post.id, {
  title: 'New title'
}, function (e, post) {
  console.log('updated', post);
});

Use db.delete to delete a particular object from database:

db.delete('posts', id, function (e, post) {
  console.log('deleted', post);
});

Why did you even make this?

Because Firebase database model is unusual, interesting and not trivial. It’s not obvious how to design an intuitive schema to manage your data in Firebase. This utility takes care of all that for you. It’s a simple ORM.

Alright, now show me the code!

Here is firebase-data.js as required above:

var Firebase = require("firebase"),
  _ = require("underscore");

module.exports = function (fbPath, types) {
  var fbRoot = new Firebase(fbPath);
  
  var db = { data: {}},
    data = db.data;
  
  types.forEach(function (type) {
    data[type] = {};
    data[type].values = [];
    data[type].ids = [];
    data[type].cloud = fbRoot.child(type);
  
    data[type].cloud.on("child_added", function (snap) {
      var remoteItem = snap.val(),
        stringified = JSON.stringify(remoteItem),
        localIndex = data[type].values.length;
      
      data[type].values[localIndex] = remoteItem;
      data[type].ids[localIndex] = snap.name();
    });
    
    data[type].cloud.on("child_removed", function (snap) {
      var remoteItem = snap.val(),
        stringified = JSON.stringify(remoteItem),
        localIds = data[type].ids,
        localItemIndex = localIds.indexOf(snap.name());
      
      if (~localItemIndex) {
        data[type].values.splice(localItemIndex, 1);
        localIds.splice(localItemIndex, 1);
      }
    });
    
    data[type].cloud.on("child_changed", function (snap) {
      var remoteItem = snap.val(),
        stringified = JSON.stringify(remoteItem),
        localIds = data[type].ids,
        localItemIndex = localIds.indexOf(snap.name());
  
      if (~localItemIndex) {
        data[type].values[localItemIndex] = remoteItem;
      }
    });
  });
  
  db.read = function (type, fn) {
    var values = data[type].values;
    fn(null, values.map(function (obj, i) {
      var id = data[type].ids[i];
      return _.extend(_.clone(obj), { id: id });
    }));
  };
  
  db.create = function (type, obj, fn) {
    var ref = data[type].cloud.push(obj, function (e) {
      if (e) return fn(e);
      fn(null, _.extend(_.clone(obj), {
        id: ref.name()
      }));
    });
  };
  
  db.update = function (type, id, attributes, fn) {
    var info = getResource(data[type], id),
      ref = info.ref,
      obj = info.obj;
    
    if (!obj)
      return fn(
        new Error("Resource not found in database"));
    
    // Can't update id
    _.extend(obj, _.omit(attributes, "id"));
    
    ref.set(obj, function (e) {
      if (e) return fn(e);
      fn(null,
        _.extend(_.clone(obj), { id: id }));
    });
  };
  
  db.delete = function (type, id, fn) {
    var info = getResource(data[type], id),
      ref = info.ref,
      obj = info.obj;
      
    if (!obj)
      return fn(
        new Error("Resource not found in database"));
    
    ref.remove(function (e) {
      if (e) return fn(e);
      fn(null,
        _.extend(_.clone(obj), { id: id }));
    });
  };
  
  function getResource(dataObj, id) {
    var index = dataObj.ids.indexOf(id),
      obj = dataObj.values[index];
    
    if (!obj) return {};
    
    return {
      ref: dataObj.cloud.child(id),
      obj: obj
    };
  }

  return db;
};

Taken from Apper source.

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