Spring Data JPA with embedded database and Spring Boot

In this post, we will create a Restful web-services which will use JPA to persist the data in the embedded database(h2). Also, you can read more on Restful web-services.

Adding pom.xml dependencies

We will add spring-boot-starter-jpa to manage dependencies. We will use h2 embedded database server for persistence.

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
  <groupId>com.h2database</groupId>
  <artifactId>h2</artifactId>
  <scope>runtime</scope>
</dependency>

Creating entities

We have three entities in the example project viz. Product, Rating, User.

@Entity
@Table(name = "product_ratings", schema = "product")
public class Rating {
  @Id
  @GeneratedValue
  @Column(name="rating_id")
  private Long ratingId;
 
  private double rating;
 
  @Column(name="product_id")
  private String productId;
 
  @Column(name="user_id")
  private String userId;
 
  public Rating() {
  
  }
 
  public Rating(Long ratingId, double rating, String productId, String userId) {
    super();
    this.ratingId = ratingId;
    this.rating = rating;
    this.productId = productId;
    this.userId = userId;
  }
  //getters, setters, toString, hashCode, equals
}

@Entity annotation specifies that this is an entity class. @Table annotation specifies the primary table for an entity class. You can configure the table_name and schema using this annotation for the entity class. @Id specifies that this field is the primary key of the entity. @GeneratedValue specifies how primary key will be generated. @Column is used to specify the mapped column for the property or field. You can also configure if the property is unique, nullable, length, precision, scale and/or if you want to insert or update it in the table.

Creating Repositories

You can extend the JpaRepository, CrudRepository interface to create your repository.

@Transactional
public interface ProductRepository extends JpaRepository<Product, String> {

}

Here, I created a ProductRepository interface which extends JpaRepository interface. You may wonder that instead of writing a repository class, we have created an interface and where will this get the implementation? The simple answer is SimpleJpaRepository class. A Proxy is generated by Spring and all the request is catered by the SimpleJpaRepository.

This contains all the basic methods like find, delete, save, findAll and few sort related/ criteria based search methods. Could be a case that you need to write your own specific method and in my case finding all the ratings of product. This could be done as follows.

@Transactional
public interface RatingRepository extends JpaRepository<Rating, Long> {
  public Iterable<Rating> getRatingsByProductId(final String productId);
}

@EnableJpaRepositories annotation

This annotation will enable JPA repositories. This will scan for Spring Data repositories in annotated configuration class by default. You can also change the basePackages to scan in this annotation.

@SpringBootApplication
@EnableJpaRepositories
public class App {
  public static void main(String[] args) {
    SpringApplication.run(App.class, args);
  }
}

In our example, we have used this annotation in our App class, so it will scan all the packages in and under com.gauravbytes.gkart

These are the few steps to create a simple JPA project. You can get the full code on Github.

Few important points

If you are using embedded server in the above example, then you may need to set the following configurations.

  • Adding schema.sql in the classpath, if you are using schema in your tables(entity classes). You can get sample here.
  • You can change the datasource name(by default testdb) and other properties. See org.springframework.boot.autoconfigure.jdbc.DataSourceProperties for full list of properties that you can configure.

No comments :

Post a Comment