[Spring] QueryDSL Introduction ( w/ Spring Data JPA, Kotlin )

Dependency

QueryDSL generates QClass that used to write typesafe query.
then, We should add annotation processor to generate QClass from entity.

 

plugins {
  ...
  kotlin("kapt") version "1.6.10"
}

dependencies {
  ...

  implementation("com.querydsl:querydsl-core")
  implementation("com.querydsl:querydsl-jpa")
  kapt(group = "com.querydsl", name = "querydsl-apt", classifier = "jpa")
  sourceSets.main {
        withConvention(org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet::class) {
            kotlin.srcDir("build/generated/source/kapt/main")
        }
  }
}

QueryDSL Configuration

To use QuerydslRepositorySupport after, We need JPAQueryFactory type Bean.

 

@Configuration
class QuerydslConfig(
    @PersistenceContext val entityManager: EntityManager
) {
  @Bean
  fun jpaQueryFactory() = JpaQueryFactory(entityManager)
}

 

If We have more than one datasource, We should qualify bean for disambiguation. ( Using @Qualifier Annotation ? )

Now Ready to use QuerydslRepositorySupport in Spring App.

Build : Generate QClass

 

gradle build

Predicate : QuerydslPredicateExecutor

 

Spring Data JPA supports QueryDSL Integration ( org.springframework.data.querydsl )

Using QuerydslPredicateExecutor interface, you can write typesafe query using Predicate.

QuerydslPredicateExecutor interface use Predicate to execution query.

For Example...

 

Optional<T> findOne(Predicate predicate)
Page<T> findAll(Predicate predicate, Pageable pageable)
Iterable<T> findAll(Predicate predicate, OrderSpecifier<?>... orders)

 

extends QuerydslPredicateExecutor interface

 

interface UserRepository: JpaRepository<User, Long>, QuerydslPredicateExecutor<User> {
  ...
}

 

then you can use Predicate in Repository.

 

fun findByUsername(username: String) {
    val predicate = QUser.user.username.like("%foo%")
    val pageable = PageRequest.of(page = 0, size = 10)
    val users = userRepository.findAll(predicate, pageable)
    users.forEach {
        it.username shouldContain "foo"
    }
}

QuerydslRepositorySupport : JpaQueryFactory

 

write complicate query in type-safe way.

 

You can write query without QuerydslRepositorySupport. just Inject JpaQueryFactory Bean.

@Repository
class UserRepositorySupport(
    @Autowired val query: JPAQueryFactory
): QuerydslRepositorySupport(User::class.java) {
  private val user = QUser.user

  fun findByUsername(username: String): User {
      val where = BooleanBuilder()
    where.and(user.username.like("%$username%")
    return query.select(user).from(user).where(where).fetchFirst()
  }
}

fetchFirst method shorten limit(1).fetchOne()