LazyLoadingTest.kt

import javax.persistence.*

@Entity
@Table(name = "member")
class Member(
    @Id
    @Column(name = "member_id")
    var id: String,

    var username: String,

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "team_id")
    var team: Team?,
)

@Entity
@Table(name = "team")
class Team(
    @Id
    @Column(name = "team_id")
    var id: String,

    var name: String,
)

fun logic(em: EntityManager, puu: PersistenceUnitUtil) {
    val member = em.find(Member::class.java, "member1")
    println(puu.isLoaded(member.team)) // 즉시 로딩 되었는지 확인
    println(member.team?.name) // 필드 접근 (지연 로딩 유발)
    println(puu.isLoaded(member.team)) // 지연 로딩 되었는지 확인
}

fun main() {
    val emf = Persistence.createEntityManagerFactory("pu")
    val persistenceUnitUtil = emf.persistenceUnitUtil
    var em = emf.createEntityManager()
    var tx = em.transaction

    try {
        tx.begin()
        logic(em, persistenceUnitUtil)
        tx.commit()
    } catch (e: Exception) {
        e.printStackTrace()
        tx.rollback()
    } finally {
        em.clear()
    }
    em.close()
    emf.close()
}