Dynamically creating spring EnversRevisionRepository from a Java Class

Question

How does one create an EnversRevisionRepository dynamically given a Java Class object?

Thanks to this answer https://stackoverflow.com/a/22342025/3771679 one can successfully create a JpaRepository dynamically, but I would like to achieve the same for a repository that is equivalent to:

public interface MyRevisionedRepository extends RevisionRepository<X,Y,Z>, JpaRepository<X,Y> {

}

Answer 1

Spring Data provides EnversRevisionRepositoryImpl as the default RevisionRepository implementation.

As you can see in the repository constructor:

    /**
     * Creates a new {@link EnversRevisionRepositoryImpl} using the given {@link JpaEntityInformation},
     * {@link RevisionEntityInformation} and {@link EntityManager}.
     *
     * @param entityInformation must not be {@literal null}.
     * @param revisionEntityInformation must not be {@literal null}.
     * @param entityManager must not be {@literal null}.
     */
    public EnversRevisionRepositoryImpl(JpaEntityInformation<T, ?> entityInformation,
            RevisionEntityInformation revisionEntityInformation, EntityManager entityManager) {

        Assert.notNull(revisionEntityInformation, "RevisionEntityInformation must not be null!");

        this.entityInformation = entityInformation;
        this.entityManager = entityManager;
    }

you need three things to create a new instance of that repository:

• An EntityManager, which you can easily obtain using @PersistenceContext or probably (I never tested it) by @Autowiring.

• A JpaEntityInformation. Following the example of SimpleJpaRepository:

final JpaEntityInformation<T, ?> entityInformation =
  JpaEntityInformationSupport.getEntityInformation(domainClass, em)

• A RevisionEntityInformation. It is curious, as the object is being asserted to not be null but actually it seems unused in the rest of the implementation code. Here, we can follow the example of EnversRevisionRepositoryFactoryBean:

final RevisionEntityInformation revisionEntityInformation =
  Optional.ofNullable(revisionEntityClass) //
    .filter(it -> !it.equals(DefaultRevisionEntity.class))//
    .<RevisionEntityInformation> map(ReflectionRevisionEntityInformation::new) //
    .orElseGet(DefaultRevisionEntityInformation::new); 

DefaultRevisionEntityInformation is package scoped, but you can easily reproduce it:

import org.hibernate.envers.DefaultRevisionEntity;
import org.springframework.data.repository.history.support.RevisionEntityInformation;

/**
 * {@link RevisionEntityInformation} for {@link DefaultRevisionEntity}.
 */
public class DefaultRevisionEntityInformation implements RevisionEntityInformation {

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.history.support.RevisionEntityInformation#getRevisionNumberType()
     */
    public Class<?> getRevisionNumberType() {
        return Integer.class;
    }

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.history.support.RevisionEntityInformation#isDefaultRevisionEntity()
     */
    public boolean isDefaultRevisionEntity() {
        return true;
    }

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.history.support.RevisionEntityInformation#getRevisionEntityClass()
     */
    public Class<?> getRevisionEntityClass() {
        return DefaultRevisionEntity.class;
    }
}

In summary:

// Obtain a reference to the underlying EntityManager
final EntityManager entityManager = ...;
// Provide JpaEntityInformation
final JpaEntityInformation<User, ?> entityInformation =
  JpaEntityInformationSupport.getEntityInformation(User.class, entityManager);
// Provide RevisionEntityInformation. The solution is based on 
// DefaultRevisionEntity but you can provide your custom revision entity
// if appropriate
final RevisionEntityInformation revisionEntityInformation =
  new DefaultRevisionEntityInformation();
// Build your custom revision repository, for example:
final RevisionRepository userRevisionRepository =
  new EnversRevisionRepositoryImpl<User, Integer, DefaultRevisionEntity>(
    entityInformation, revisionEntityInformation, entityManager
  )
;