spring-data-jpa-examples

Spring Data JPA Examples

An example of some complicated aspects of Spring Data JPA such as

• fetching strategies of @OneToMany and @ManyToMany collections
• locking strategies
• entity to DTO mapping

Prerequisites

• JDK 11
• Docker at least 1.6.0

How to run tests

To build project and run all tests use command

./gradlew cleanTest test -i

Implementation details

• JDK 11
• Spring Boot 2.2.x
• Spring Data JPA 2.2.x
• MapStruct 1.3.1.Final
• JUnit 5
• Testcontainers

This example has a simple domain model. A book has at least one author and belongs to at least one category. A book can be rated. An average rating and a total number of ratings are tracked.

Simplified UML class diagram

Many-to-many relationship List<Author> authors has javax.persistence.FetchType.EAGER and many-to-many relationship Set<Category> categories has javax.persistence.FetchType.LAZY.

To demonstrate how different org.hibernate.annotations.FetchModes work the hierarchy of book classes used:

• com.example.spring.data.jpa.entity.AbstractBook - @MappedSuperclass
• com.example.spring.data.jpa.entity.Book - no explicit @Fetch
• com.example.spring.data.jpa.entity.BookWithFetchModeJoin - @Fetch(JOIN)
• com.example.spring.data.jpa.entity.BookWithFetchModeSelect - @Fetch(SELECT)
• com.example.spring.data.jpa.entity.BookWithFetchModeSubselect - @Fetch(SUBSELECT)
• com.example.spring.data.jpa.entity.BookWithBatchSize - @BatchSize
• com.example.spring.data.jpa.entity.BookWithMultipleBags - doesn't extend AbstractBook and has List<Category> categories instead of Set like in AbstractBook and its children what leads to MultipleBagFetchException: cannot simultaneously fetch multiple bags when both relations are fetched using join.

To demonstrate locking strategies a com.example.spring.data.jpa.entity.BookRating class has @Version int version field.

Actual UML class diagram

Entity-relationship diagram

Test cases

• Fetching strategies
  • Entity without explicit @Fetch - com.example.spring.data.jpa.BookRepositoryTest
    • CrudRepository.findById
    • Query method
    • Query method with @EntityGraph
    • Query method with @EntityGraph and Pageable
    • Query method with @EntityGraph with multiple attribute nodes (issue HHH-13740)
    • @Query with JPQL join fetch
    • @Query with JPQL join fetch and distinct
    • Custom @Repository with Criteria API query
    • Custom @Repository with Criteria API query with fetch
    • Custom @Repository with Criteria API query with fetch and distinct
    • Mapping from entity to DTO using MapStruct
  • Entity with @Fetch(JOIN) - com.example.spring.data.jpa.BookWithFetchModeJoinRepositoryTest
    • CrudRepository.findById
    • Query method
  • Entity with @Fetch(SELECT) - com.example.spring.data.jpa.BookWithFetchModeSelectRepositoryTest
    • CrudRepository.findById
    • Query method
  • Entity with @Fetch(SUBSELECT) - com.example.spring.data.jpa.BookWithFetchModeSubselectRepositoryTest
    • CrudRepository.findById
    • Query method
  • Entity with @BatchSize - com.example.spring.data.jpa.BookWithBatchSizeRepositoryTest
    • CrudRepository.findById
    • Query method
  • Entity with multiple bags (two @ManyToMany collections with type List) resulting in MultipleBagFetchException - com.example.spring.data.jpa.BookWithMultipleBagsRepositoryTest
• Locking strategies - com.example.spring.data.jpa.BookRatingRepositoryTest
  • Implicit optimistic lock of entity with @Version on modification
  • Explicit optimistic lock @Lock(OPTIMISTIC)
  • Explicit optimistic lock @Lock(OPTIMISTIC_FORCE_INCREMENT)
  • Explicit pessimistic write lock @Lock(PESSIMISTIC_WRITE)
  • Explicit pessimistic read lock @Lock(PESSIMISTIC_READ)