Throughout this chapter, we touched upon the basics of querying three very different database systems.
The MySQL database has been around for a very long time, and is likely the number one database for most PHP applications. Its ACID compliance makes it irreplaceable for applications dealing with financial or other sensitive data where atomicity, consistency, isolation, and durability are key factors.
Mongo, on the other hand, tackles data storage through a schema-less approach. This makes it much easier for developers to pace up application development, although the lack of ACID compliance across documents limits its use in certain types of applications.
Finally, the Redis data store serves as a great caching, or even a session-storing solution for our applications.
Moving forward, we will take a closer look at dependency injection, what it is, and...
