Android App – Connecting to SQL Server Guidance

You've run into a problem that many have before you...a database optimized for reading is seldom good for write efficiency and vice versa. One approach that has evolved from this read-write impediment is CQRS (Command Query Responsibility Segregation). Despite Wikipedia linking the two together CQRS and CQS are technically different. CQS just demands that a method either make a change (command) or ask information (query) never both.

CQRS takes it a step further and specifies that you have a separate model for Queries and Commands. This single step enables things like separating your read and write database. Which is what you want to do.

I can't say that I'm an expert on Mongo or configuring it to work with SQL Server. But from my understanding, people use Mongo as a denormalized view of their transactional database. Updating Mongo from the transactional db might come down to running a SQL Agent. Or having a separate service to poll the database.

An even better alternative would be to have your Command service fire an event whenever an update is made. You would then have a service that listened for that event and updated the MongoDB with that information. That is the fundamental approach to Event Sourcing (search for Event Sourcing on the page).

Greg Young, one of the thought leaders in the DDD world is currently writing a book in the Fowler Signature Series on CQRS called Event-Centric (it used to be called CQRS). Fowler has written a post on his bliki describing the approach

Django's admin interface for the CRUD admin website, an RPC-like mechanism for communicating with a server-side API from the clients, probably there are decent libraries to export Django methods over XMLRPC (something like http://pypi.python.org/pypi/django-xmlrpc)