Question

I’m used to using relational databases like MySQL or PostgreSQL, and combined with MVC frameworks such as Symfony, RoR or Django, and I think it works great.

But lately I’ve heard a lot about MongoDB which is a non-relational database, or, to quote the official definition,

a scalable, high-performance, open
source, schema-free, document-oriented
database.

I’m really interested in being on edge and want to be aware of all the options I’ll have for a next project and choose the best technologies out there.

In which cases using MongoDB (or similar databases) is better than using a “classic” relational databases?
And what are the advantages of MongoDB vs MySQL in general?
Or at least, why is it so different?

If you have pointers to documentation and/or examples, it would be of great help too.

Answer 1

Here are some of the advantages of MongoDB for building web applications:

1. A document-based data model. The basic unit of storage is analogous to JSON, Python dictionaries, Ruby hashes, etc. This is a rich data structure capable of holding arrays and other documents. This means you can often represent in a single entity a construct that would require several tables to properly represent in a relational db. This is especially useful if your data is immutable.
2. Deep query-ability. MongoDB supports dynamic queries on documents using a document-based query language that’s nearly as powerful as SQL.
3. No schema migrations. Since MongoDB is schema-free, your code defines your schema.
4. A clear path to horizontal scalability.

You’ll need to read more about it and play with it to get a better idea. Here’s an online demo:

http://try.mongodb.org/