How it works...

Even though, by default, Spring Boot makes certain assumptions about the database configuration by examining the classpath for the presence of supported database drivers, it provides you with easy configuration options to tweak the database access via a set of exposed properties grouped under spring.datasource.

The things that we can configure are url, username, password, driver-class-name, and so on. If you want to consume the datasource from a JNDI location, where an outside container creates it, you can configure this using the spring.datasource.jndi-name property. The complete set of possible properties is fairly large, so we will not go into all of them. However, we will cover more options in Chapter 5, Application Testing, where we will talk about mocking data for application tests using a database.

If you want to connect to a regular (non-embedded) database, besides just having the appropriate driver library in the classpath, we need to specify the driver of our choice in the configuration. The following code snippet is what the configuration to connect to MySQL would resemble:

    spring.datasource.driver-class-name: com.mysql.jdbc.Driver
    spring.datasource.url:   
    jdbc:mysql://localhost:3306/springbootcookbook
    spring.datasource.username: root
    spring.datasource.password:
  

If we wanted Hibernate to create the schema automatically, based on our entity classes, we would need to add the following line to the configuration:

    spring.jpa.hibernate.ddl-auto=create-drop
  

You can go even further in the abstraction layer and, instead of autowiring a DataSource object, you could go straight for  JdbcTemplate. This would instruct Spring Boot to automatically create a DataSource and then create a JdbcTemplate wrapping the datasource, thus providing you with a more convenient way of interacting with a database in a safe way. The code for JdbcTemplate is as follows:

@Autowired 
private JdbcTemplate jdbcTemplate; 

You can also look in the spring-boot-autoconfigure source at an org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration file to see the code behind the datasource creation magic.