guide repository

Table of Contents

• Spring Data
  • Motivation
  • Dependency
  • Repository
  • Custom method implementation
    • Example
    • Integration of Spring Data in devon4j-spring
    • Custom methods without fragment approach
  • Drawbacks
  • Limitations in Quarkus

Spring Data

Spring Data JPA is supported by both Spring and Quarkus. However, in Quarkus this approach still has some limitations. For detailed information, see the official Quarkus Spring Data guide.

Motivation

The benefits of Spring Data are (for examples and explanations see next sections):

• All you need is one single repository interface for each entity. No need for a separate implementation or other code artifacts like XML descriptors, NamedQueries class, etc.

• You have all information together in one place (the repository interface) that actually belong together (where as in the classic approach you have the static queries in an XML file, constants to them in NamedQueries class and referencing usages in DAO implementation classes).

• Static queries are most simple to realize as you do not need to write any method body. This means you can develop faster.

• Support for paging is already build-in. Again for static query method the is nothing you have to do except using the paging objects in the signature.

• Still you have the freedom to write custom implementations via default methods within the repository interface (e.g. for dynamic queries).

Dependency

In case you want to switch to or add Spring Data support to your Spring or Quarkus application, all you need is to add the respective maven dependency:

spring

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

quarkus

<dependency>
  <groupId>io.quarkus</groupId>
  <artifactId>quarkus-spring-data-jpa</artifactId>
</dependency>

Repository

For each entity «Entity»Entity an interface is created with the name «Entity»Repository extending JpaRepository. Such repository is the analogy to a Data-Access-Object (DAO) used in the classic approach or when Spring Data is not an option.

Repository

public interface ProductRepository extends JpaRepository<ProductEntity, Long> {

}

The Spring Data repository provides some basic implementations for accessing data, e.g. returning all instances of a type (findAll) or returning an instance by its ID (findById).

Custom method implementation

In addition, repositories can be enriched with additional functionality, e.g. to add QueryDSL functionality or to override the default implementations, by using so called repository fragments:

Example

The following example shows how to write such a repository:

Repository

public interface ProductRepository extends JpaRepository<ProductEntity, Long>, ProductFragment {

  @Query("SELECT product FROM ProductEntity product" //
      + " WHERE product.title = :title")
  List<ProductEntity> findByTitle(@Param("title") String title);

  @Query("SELECT product FROM ProductEntity product" //
      + " WHERE product.title = :title")
  Page<ProductEntity> findByTitlePaginated(@Param("title") String title, Pageable pageable);
}

Repository fragment

public interface ProductFragment {
  Page<ProductEntity> findByCriteria(ProductSearchCriteriaTo criteria);
}

Fragment implementation

public class ProductFragmentImpl implements ProductFragment {
  @Inject
  EntityManager entityManager;

  public Page<ProductEntity> findByCriteria(ProductSearchCriteriaTo criteria) {
    QProductEntity product = QProductEntity.productEntity;
    JPAQuery<ProductEntity> query = new JPAQuery<ProductEntity>(this.entityManager);
    query.from(product);

    String title = criteria.getTitle();
    if ((title != null) && !title.isEmpty()) {
      query.where(product.title.eq(title));
    }

    List<ProductEntity> products = query.fetch();
    return new PageImpl<>(products, PageRequest.of(criteria.getPageNumber(), criteria.getPageSize()), products.size());
  }
}

This ProductRepository has the following features:

• CRUD support from Spring Data (see JavaDoc for details).

• Support for QueryDSL integration, paging and more.

• A static query method findByTitle to find all ProductEntity instances from DB that have the given title. Please note the @Param annotation that links the method parameter with the variable inside the query (:title).

• The same with pagination support via findByTitlePaginated method.

• A dynamic query method findByCriteria showing the QueryDSL and paging integration into Spring via a fragment implementation.

You can find an implementation of this ProductRepository in our Quarkus reference application.

Note	In Quarkus, native and named queries via the @Query annotation are currently not supported

Integration of Spring Data in devon4j-spring

For Spring applications, devon4j offers a proprietary solution that integrates seamlessly with QueryDSL and uses default methods instead of the fragment approach. A separate guide for this can be found here.

Custom methods without fragment approach

The fragment approach is a bit laborious, as three types (repository interface, fragment interface and fragment implementation) are always needed to implement custom methods. We cannot simply use default methods within the repository because we cannot inject the EntityManager directly into the repository interface.

As a workaround, you can create a GenericRepository interface, as is done in the devon4j jpa-spring-data module.

public interface GenericRepository<E> {

  EntityManager getEntityManager();

  ...
}

public class GenericRepositoryImpl<E> implements GenericRepository<E> {

  @Inject
  EntityManager entityManager;

  @Override
  public EntityManager getEntityManager() {

    return this.entityManager;
  }

  ...
}

Then, all your repository interfaces can extend the GenericRepository and you can implement queries directly in the repository interface using default methods:

public interface ProductRepository extends JpaRepository<ProductEntity, Long>, GenericRepository<ProductEntity> {

  default Page<ProductEntity> findByTitle(Title title) {

    EntityManager entityManager = getEntityManager();
    Query query = entityManager.createNativeQuery("select * from Product where title = :title", ProductEntity.class);
    query.setParameter("title", title);
    List<ProductEntity> products = query.getResultList();
    return new PageImpl<>(products);
  }

  ...
}

Drawbacks

Spring Data also has some drawbacks:

• Some kind of magic behind the scenes that are not so easy to understand. So in case you want to extend all your repositories without providing the implementation via a default method in a parent repository interface you need to deep-dive into Spring Data. We assume that you do not need that and hope what Spring Data and devon already provides out-of-the-box is already sufficient.

• The Spring Data magic also includes guessing the query from the method name. This is not easy to understand and especially to debug. Our suggestion is not to use this feature at all and either provide a @Query annotation or an implementation via default method.

Limitations in Quarkus

• Native and named queries are not supported using @Query annotation. You will receive something like: Build step io.quarkus.spring.data.deployment.SpringDataJPAProcessor#build threw an exception: java.lang.IllegalArgumentException: Attribute nativeQuery of @Query is currently not supported

• Customizing the base repository for all repository interfaces in the code base, which is done in Spring Data by registering a class the extends SimpleJpaRepository