Why not mongodb?

Question

I recently used MongoDB for the first time and found it exceptionally easy to use and high-performing. Which leads to my question - why not MongoDB?

Lets say I am implementing a Q & A app. My approach would be to implement the User data in a MySQL database and then use MongoDB for the question and answer storage - one collection storing a question and all responses.

Is there anything wrong with this approach?

Answer 1

MongoDB sounds like a fine application for your problem, but there are plenty of reasons why you would not use it.

MongoDB would not be well suited for applications that need:

1. Multi-Object Transactions: MongoDB only supports ACID transactions for a single document.
2. SQL: SQL is well-known and a lot of people know how to write very complex queries to do lots of things. This knowledge is transferrable across a lot of implementations where MongoDB's queries language are specific to it.
3. Strong ACID guarantees: MongoDB allows for things like inconsistent reads which is fine in some applications, but not in all.
4. Traditional BI: A lot of very powerful tools exist that allow for OLAP and other strong BI applications and those run against traditional SQL database.