我正在使用Hotnate和Kotlin，我在FetchType.LAZY @ManyToOne关系上遇到问题。请考虑以下事项：
@ManyToOne(fetch = FetchType.LAZY)
open var event: Event?
问题是，当使用FetchType.LAZY时，提取的Event将属于Event_$$_jvst_...类JavaassistLazyInitializer。但事件永远不会被初始化，一切都将为null或为空。
FetchType.LAZY后，一切正常。open上添加var，以便Event可以正确代理。没效果。@Entity课程当然也是open。如果删除open关键字，则不会创建任何代理，因此不会出现懒惰。我的猜测是Hibernate无法轻易代理这些默认的kotlin getter。有办法解决吗？
答案 0 :(得分：0)
您可以使用此静态方法来对您的实体进行描述
/**
* Utility method that tries to properly initialize the Hibernate CGLIB
* proxy.
* @param <T>
* @param maybeProxy -- the possible Hibernate generated proxy
* @param baseClass -- the resulting class to be cast to.
* @return the object of a class <T>
* @throws ClassCastException
*/
public static <T> T deproxy(Object maybeProxy, Class<T> baseClass) throws ClassCastException {
if (maybeProxy instanceof HibernateProxy) {
return baseClass.cast(((HibernateProxy) maybeProxy).getHibernateLazyInitializer().getImplementation());
}
return baseClass.cast(maybeProxy);
}
答案 1 :(得分：0)
我写了一个简单的例子来检查你的问题，一切正常。
import org.hibernate.CacheMode
import org.hibernate.Session
import org.hibernate.SessionFactory
import org.hibernate.Transaction
import org.hibernate.boot.MetadataSources
import org.hibernate.boot.registry.StandardServiceRegistryBuilder
import org.hibernate.cfg.Environment
import java.util.*
import javax.persistence.*
fun main(args: Array<String>) {
val standardServiceRegistryBuilder = StandardServiceRegistryBuilder()
val settings = HashMap<String, String>().apply {
put(Environment.DRIVER, "org.h2.Driver")
put(Environment.URL, "jdbc:h2:mem:myDb;DB_CLOSE_DELAY=-1")
put(Environment.USER, "sa")
put(Environment.PASS, "sa")
put(Environment.DIALECT, "org.hibernate.dialect.H2Dialect")
put(Environment.SHOW_SQL, "true")
put(Environment.HBM2DDL_AUTO, "create")
}
val sessionFactory = standardServiceRegistryBuilder.applySettings(settings)
.build()
.let {
MetadataSources(it).apply {
addAnnotatedClass(History::class.java)
addAnnotatedClass(Event::class.java)
}
}
.run { metadataBuilder.build() }
.run { sessionFactoryBuilder.build() }
sessionFactory.inSession {
inTransaction { session ->
session.save(Event(1, "event description"))
session.save(History(1, Event(1), "history description"))
}
}
sessionFactory.inSession {
inTransaction { session ->
val entity = session.get(Event::class.java, 1L)
println("=============1=============")
println(entity)
}
}
sessionFactory.inSession {
inTransaction { session ->
val entity = session.load(History::class.java, 1L)
println("=============2=============")
println(entity)
}
}
}
private fun SessionFactory.inSession(function: Session.() -> Unit) {
val session = this.openSession()
session.function()
session.close()
}
private fun Session.inTransaction(function: Transaction.(s: Session) -> Unit) {
val transaction = this.beginTransaction()
transaction.function(this)
transaction.commit()
}
@Entity
open class History(
@Id
open var id: Long? = null,
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "eventId")
open var event: Event? = null,
open var description: String = ""
) {
override fun toString(): String {
return "History(id=$id, event=$event, description='$description')"
}
}
@Entity
open class Event(
@Id
open var id: Long? = null,
open var description: String? = null,
@OneToMany(fetch = FetchType.LAZY, mappedBy = "event")
open var history: MutableSet<History>? = null
) {
override fun toString(): String {
return "Event(id=$id, description='$description', history=${history?.size})"
}
}
日志如下所示：
2017-12-05 18:43:03 [main] INFO org.hibernate.Version - HHH000412: Hibernate Core {5.2.12.Final}
2017-12-05 18:43:03 [main] INFO org.hibernate.cfg.Environment - HHH000206: hibernate.properties not found
2017-12-05 18:43:03 [main] INFO o.h.annotations.common.Version - HCANN000001: Hibernate Commons Annotations {5.0.1.Final}
2017-12-05 18:43:04 [main] WARN o.hibernate.orm.connections.pooling - HHH10001002: Using Hibernate built-in connection pool (not for production use!)
2017-12-05 18:43:04 [main] INFO o.hibernate.orm.connections.pooling - HHH10001005: using driver [org.h2.Driver] at URL [jdbc:h2:mem:myDb;DB_CLOSE_DELAY=-1]
2017-12-05 18:43:04 [main] INFO o.hibernate.orm.connections.pooling - HHH10001001: Connection properties: {password=****, user=sa}
2017-12-05 18:43:04 [main] INFO o.hibernate.orm.connections.pooling - HHH10001003: Autocommit mode: false
2017-12-05 18:43:04 [main] INFO o.h.e.j.c.i.DriverManagerConnectionProviderImpl - HHH000115: Hibernate connection pool size: 20 (min=1)
2017-12-05 18:43:04 [main] INFO org.hibernate.dialect.Dialect - HHH000400: Using dialect: org.hibernate.dialect.H2Dialect
2017-12-05 18:43:04 [main] INFO o.h.validator.internal.util.Version - HV000001: Hibernate Validator 5.3.5.Final
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by javassist.util.proxy.SecurityActions (file:/Users/evgenyzaharov/.gradle/caches/modules-2/files-2.1/org.javassist/javassist/3.20.0-GA/a9cbcdfb7e9f86fbc74d3afae65f2248bfbf82a0/javassist-3.20.0-GA.jar) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
WARNING: Please consider reporting this to the maintainers of javassist.util.proxy.SecurityActions
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Hibernate: drop table Event if exists
2017-12-05 18:43:04 [main] INFO org.hibernate.orm.connections.access - HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@56913163] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Hibernate: drop table History if exists
Hibernate: create table Event (id bigint not null, description varchar(255), primary key (id))
2017-12-05 18:43:04 [main] INFO org.hibernate.orm.connections.access - HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@e8e0dec] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Hibernate: create table History (id bigint not null, description varchar(255), eventId bigint, primary key (id))
Hibernate: alter table History add constraint FK2yaqfgh2x1lsxcpbuifmd245k foreign key (eventId) references Event
2017-12-05 18:43:04 [main] INFO o.h.t.s.internal.SchemaCreatorImpl - HHH000476: Executing import script 'org.hibernate.tool.schema.internal.exec.ScriptSourceInputNonExistentImpl@6c15e8c7'
Hibernate: select event_.id, event_.description as descript2_0_ from Event event_ where event_.id=?
Hibernate: insert into Event (description, id) values (?, ?)
Hibernate: insert into History (description, eventId, id) values (?, ?, ?)
Hibernate: update History set description=?, eventId=? where id=?
Hibernate: select event0_.id as id1_0_0_, event0_.description as descript2_0_0_ from Event event0_ where event0_.id=?
=============1=============
Hibernate: select history0_.eventId as eventId3_1_0_, history0_.id as id1_1_0_, history0_.id as id1_1_1_, history0_.description as descript2_1_1_, history0_.eventId as eventId3_1_1_ from History history0_ where history0_.eventId=?
Event(id=1, description='event description', history=1)
=============2=============
Hibernate: select history0_.id as id1_1_0_, history0_.description as descript2_1_0_, history0_.eventId as eventId3_1_0_ from History history0_ where history0_.id=?
Hibernate: select event0_.id as id1_0_0_, event0_.description as descript2_0_0_ from Event event0_ where event0_.id=?
Hibernate: select history0_.eventId as eventId3_1_0_, history0_.id as id1_1_0_, history0_.id as id1_1_1_, history0_.description as descript2_1_1_, history0_.eventId as eventId3_1_1_ from History history0_ where history0_.eventId=?
History(id=1, event=Event(id=1, description='event description', history=1), description='history description')
Lazy初始化仅在显式获取值后开始加载字段数据。
希望这会对你有所帮助。