This shows how to add a simple datasource to the project.

To have this working, we'll need to import the starter-data-jpa dependency. It adds DB support, JPA and autoconfigured datasources. Moreover adds HikariCP connection pool, preferred by Spring Boot by its high performance.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

An in memory DB is very useful for tests. In Booter it's also used as a default database for the application - unless a different datasource is defined.

If Spring Boot developer tools are in the classpath the H2 web console will be enabled at the endpoint /h2-console, with the user and password defined in the datasource.

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
</dependency>`

A real DB could be MySQL. Importing the connector allows defining a datasource for this DB.

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

Spring Data JPA it's configured as shown below. Maybe the most important property is ddl-auto which says what to do with the DB at application startup: update it, create new tables and relationships, or drop them all and create everything after that.

spring:
  jpa:
    hibernate:
      show-sql: false # Hide Hibernate logs but if log level is DEBUG this will be ignored.
      format-sql: true # Beautify ugly Hibernate queries.
      ddl-auto: update # none, update, create, create-drop.

By default, only a single datasource is configured in a Spring Boot application and it will be on a bean of type Datasource, with the name datasource. It can be injected where needed.

spring:
  datasource:
    url: jdbc:h2:mem:~/test
    username: sa
    password:
    driver-class-name: org.h2.Driver

This extract from the logging configuration shows how to do to make Hibernate to log SQL queries and besides log the real values used in the query parameters.

logging:
  level:
    org.hibernate.SQL: DEBUG # To show SQL queries.
    org.hibernate.type.descriptor.sql.BasicBinder: TRACE # And their param values.