Todd Anderson

I make things for the web, mobile, desktop and land.

Announcing as3couchdb Library

2010 April 13th by todd anderson

The library is available on github at bustardcelly/as3couchdb. You can read more detailed information on the wiki. Continue reading to hear me blab on and on.

When the new year came and i had finally got in my last chapter for Flex 4 Cookbook, it was time to return to my list of things to learn. I started looking into Capuccino and Closure and bought a book on Python. Somewhere along the way i just clicked on some tweet about 5 emerging trends that i must know about. Usually i find these lists are a grain-of-salt bandwagon of buzzery – maybe some truth but can’t cut through the true meaning of why this person is writing about them. But one did stick – NoSQL. I looked into the different implementations and right away i took a fancy to CouchDB. I don’t know why. It seemed quite simple. Working with a database using REST calls. Sounds good. And i could write my own map-reduce views in Javascript. Sign me up.

What also was a big draw to me was the concept of document revisions in CouchDB. I had worked on a couple projects that required online/offline synchronization and it was quite a pain to keep track of last modified entries and cleanup of deleted entries in a SQL database. The revisioning system for documents (entries) is built into CouchDB and what is more is that you are not locked into a rigid data structure and ensure your table relations are scalable. That’s not to say that building relational databases isn’t a fine art. It is. And there are many smarter people than me that get paid more money that have that craft. I don’t. The concept of revisions is familiar to me and i am greatly intrigued by the concept of NoSQL.

Anyway, i started digging into CouchDB and figured the one way for me to see the whole picture was to hook up a client side end to make these requests. See if what i was reading about was something i could use as a different approach to online/offline synchronization in my applications. What came out was a whole library for working with databases and documents of a CouchDB instance – a library which is now available on github at http://github.com/bustardcelly/as3couchdb.

Took me long enough to get talking about the as3couchdb library mentioned in the title, didn’t it? Well, you can read more long-winded explanations about the make-up of the library from the wiki on github, and browse some examples that use the library (currently all Flex examples, but AS3 examples are coming soon).

If you are still around, i can give a brief synopsis of the project:

When i set out on creating the as3couchdb library, i knew i wanted to follow a similar approach to Data Access Objects. I wanted to make all my requests through the object i was working with and have an intermediate layer that communicate with the service and updated the object accordingly. To achieve this, i went about creating a base model class that contains a model entity. The model entity is really only involved in parsing custom metadata and resolving the information to properties held on the base model. Extending the base model are the two core models of CouchDB that you interact with: the Database and the Document.

So the Database and Document models can be though of as the Business Objects and expose methods that related to CRUD operations. Even though CouchDB has a REST API, i chose using simple CRUD method signitures on the models as they seem easier to read and understand. From these methods, the models interact with a service mediator (similar to Data Access Object), which knows how to communicate with the service proxy and has action handlers that know how to modify the model once a successful result is received. To put it in code terms:

I wanted to have the ease of creating and storing a document as such

var contact:ContactDocument = new ContactDocument(); contact.firstName = "Todd"; contact.lastName = "Anderson"; contact.addEventListener(CouchActionType.CREATE, handleContactCreate); contact.create();

And the ease to simply read in for modification as such:

var contact:ContactDocument = new ContactDocument(); contact.addEventListener(CoachActionType.READ, handleContactRead); contact.read( $uid );

In order to make this all work and auto-wire the models with a service mediator, custom annotations were needed. This is where the model entity mentioned earlier comes into play. When extending the core models (as ContactDocument does in the previous examples) you add custom metadata that relates to the CouchDB instance you intend to work with and the fully qualified classnames of the target service mediator and request object.

Now the request object is a different story and was brought into the picture due to the lack of HTTP method types available for the web version of Flash Player. As such, there are a couple different request object types available in as3couchdb: straight-up devil-may-care requests using URLRequest (mainly for AIR or you will get RTEs), one that uses External Interface, and one that uses as3httpclientlib. The as3httpclientlib allows you to make PUT and DELETE requests using a Socket and is the best way to interact with a RESTful service when limited to the Flash web player (imho).

So that is a brief rundown of the model and business layer implementation i strove for when creating as3couchdb. As i mentioned way back in upward-page-scroll land, the original drive to make as3couchdb was to see if i could ease up the pain of developing an application that uses online/offline synchronization. That is in the works and maybe this blog will become a little more active as I dive into that task.

If you made it this far, thank you for reading all this. Wow. You are a trooper. Tell your boss i said it is okay and you can bill that time.

Link-link time!
CouchDB – http://couchdb.apache.org/
CouchDB: The Definitive Guide – http://books.couchdb.org/relax/
CouchDB: Wiki – http://wiki.apache.org/couchdb/FrontPage
Planet CouchDB – http://planet.couchdb.org/
MongoDB, CouchDB and MySQL Compare Grid – http://www.mongodb.org/display/DOCS/MongoDB,+CouchDB,+MySQL+Compare+Grid
as3httpclientlib – http://github.com/gabriel/as3httpclient

More information about the custom metadata, and the inner workings of as3couchdb can be found on the wiki for the project in github.

Posted in AS3, CouchDB, Flash, Flex, as3couchdb.