Spring Data JPA

Let’s go over the Spring Data JPA, as well as its setup and integration with the H2 database.

We'll cover the following

What is Spring Data JPA?

The Spring Data JPA provides JPA-based data access layers via generic repositories. By implementing a Repository interface in a Data Access Object (DAO), the DAO can have CRUD features with paginationThe process of dividing a sizeable response into small data chunks called pages, with sequences to move from one page to another. and sorting capabilities.

Therefore, using the Spring Data JPA reduces a lot of boilerplate code, and less configuration is required to create the basic data access layer.

Setup

Let’s quickly refresh our understanding of the dependencies required for the database integration.

To use the Spring Data JPA in our Spring Boot application, todo, we first need to add the spring-boot-starter-data-jpa dependency in our build.gradle. Also, for the database engine, we’ll need to add the H2 dependency.

plugins {
    id 'org.springframework.boot' version '2.6.2'
    id 'io.spring.dependency-management' version '1.0.11.RELEASE'
    id 'java'
}
group = 'io.educative'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'
repositories {
    mavenCentral()
}
dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
    implementation 'org.springframework.boot:spring-boot-starter-validation'
    implementation 'org.springframework.boot:spring-boot-starter-web'
    compileOnly 'org.projectlombok:lombok'
    runtimeOnly 'com.h2database:h2'
    annotationProcessor 'org.projectlombok:lombok'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
}
test {
    useJUnitPlatform()
}

H2 database configuration

In this section, we’ll take a close look at the setup and configuration of the H2 database in our todo application.

The H2 setup

Now that we’ve added the H2 database engine in the build.gradle, let’s discuss a few spring.datasource properties to configure the database URL and credentials.

Let’s look at the application.properties:

spring.datasource.url=jdbc:h2:~/testdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

Alternatively, we can also use application.yml for similar Spring configurations.

spring:
  datasource:
    url: jdbc:h2:~/testdb
    username: sa
    password: password
    driverClassName: org.h2.Driver
  jpa:
    database-platform: org.hibernate.dialect.H2Dialect

To keep this course simple, we’ve integrated the H2 database engine to provide the in-memory data source to our todo application. Of course, we can integrate other databases like MySQL and PostgreSQL by using the relevant database connector dependencies.

The H2 console

Once the configuration for the H2 database is added, we can restart the application and connect it to the database. As an extra feature of our application that proves quite handy in its development, the H2 embedded database also provides an built-in, UI-based console to access the database using the browser.

We can enable the H2 console by using the spring.h2.console.enabled property in the application.properties/application.yml.

spring.datasource.url=jdbc:h2:~/testdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.h2.console.enabled=true

Hibernate setup

Further, let’s discuss a few useful properties to configure extra features of Hibernate in our todo application.

spring.datasource.url=jdbc:h2:~/testdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.h2.console.enabled=true
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true
spring.jpa.hibernate.ddl-auto=create

For instance, by using the spring.jpa.show-sql property we can enable Hibernate to show the underlying SQL. Similarly, SQL formatting is configurable in Hibernate with the spring.jpa.properties.hibernate.format_sql property.

Last, we can enable Hibernate to manage the database schema by using the spring.jpa.hibernate.ddl-auto property. It allows values like create, update, create-drop, and validate to create, update, drop, and validate the database schema automatically (based on the entities available).