Add `EntityInformationAware` interface to get `EntityInformation<T, ID>` in custom repository

[ars-java]

I wanna create MyBaseRepository<T,ID> having custom JPA methods but I wanna use it as base repository just for few repositories, not all because I don't wanna use @EnableJpaRepositories(repositoryBaseClass = ...) for it. But there's a problem when I try to implement generic methods in such custom repository.

interface MyEntityRepository: JpaRepository<MyEntity, MyId>, MyCustomJpaRepository<MyEntity, MyId>

@NoRepositoryBean
interface MyCustomJpaRepository<T, ID : Serializable> : JpaRepository<T, ID> {
    fun myMethod(id: ID): T?
}

class MyCustomJpaRepositoryImpl<T, ID : Serializable>(
    @Autowired private val entityManager: EntityManager,
) : MyCustomJpaRepository<T, ID> {

    override fun myMethod(id: ID): T? {
        val entity = entityManager.find(clazz, albumId) ?: return null // No Class<T> here and no way to get it in runtime
        entityManager.remove(entity)
        return entity as T
    }
}

We can add to Spring Data interface to solve this problem (analog of other Spring Aware interfaces):

interface EntityInformationAware<T, ID> {
    void setEntityInformation(entityInformation: EntityInformation<T, ID>);
}

and process its existence during repository instance creation.

Then everybody can use EntityInformation, not framework implementations.

class MyCustomJpaRepositoryImpl<T, ID : Serializable>(
    @Autowired private val entityManager: EntityManager,
) : MyCustomJpaRepository<T, ID>, EntityInformationAware<T, ID> {
    private lateinit val entityInformation: EntityInformation<T, ID>

    override fun setEntityInformation(entityInformation: EntityInformation<T, ID>) {
        this.entityInformation = entityInformation
    }

    override fun myMethod(id: ID): T? {
        val type = entityInformation.javaType as JpaEntityInformation<T, ID>
        val entity = entityManager.find(type, albumId) ?: return null // Now we know Class<T> of Entity
        entityManager.remove(entity)
        return entity as T
    }
}

[mp911de]

That's not going to work as the lifecycle scope of a fragment is different than the one of the SimpleJpaRepository. Fragments are beans in the application context while a repository is being created as instance for a particular repository interface. Multiple repositories therefore can use the same fragment instance. You can however use RepositoryMethodContext.getContext() to obtain method-call-level metadata by either letting your fragment implement the RepositoryMetadataAccess interface or enabling metadata access on the repository factory.