In the previous two chapters, we talked extensively about our options as Drupal 8 module developers for modeling and storing data in Drupal 8. We also saw some examples of how to use things such as the State, Configuration, and Entity APIs, going into greater detail about the latter by using it to build something useful. One of the key takeaways from those chapters is that the need for custom database tables and/or direct queries against them and the database has become minimal.

The Entity system is much more flexible and robust, the combination of configuration and content entities providing much of the needs for storing data. Moreover, the Entity query and loading mechanisms have also made finding them easy. Odds are, this is enough for most of your use cases.

Furthermore, storage subsystems such as the State API (key/value) and UserData have also removed much of the need to create custom tables to store that kind of "one-off" data. Also, the Configuration API provides a unified way to model exportable data, leaving no need for anything else.

However, apart from these features, Drupal also has a strong Database API that actually powers them under the hood. This API is made available to us in case we need it. For example, we can create our own database tables and then run queries against them however we want, all through a secure layer that can work on top of multiple types of databases.

Creating custom database tables is not something you will do very often— maybe never— but in this chapter, you will still learn how the API works in order to do so. There are contributed modules out there that have legitimate uses for them, and who knows, you might also. So, it is still important to understand this system. However, even more pertinent is the API for running queries (particularly select queries), because you may need to run these, even against entities. There are times in which the entity query does not provide all you need, so looking up entities based on complex queries can, in fact, be more common. Hence, we will cover how to do that in this chapter, as well.

More concretely, in this chapter, we will start by creating a couple of database tables so that we can see how the Schema API works in Drupal 8. For D7 developers, this will look strikingly familiar. Then, we will see the various ways we can perform queries against these tables by using the database abstraction layer. We can make two different types of select query, and we will practice both. For the others (INSERT, UPDATE, and DELETE), there is a standard way of doing it. Next, we will take a look at how queries can be altered and how we can tag them for better targeting. Finally, we will look at the database update hooks, which were one of the principal ways configuration was deployed in previous versions of Drupal. In reality, the purpose of these hooks is to make database updates once the tables have already been created.