Java 与Kotlin一起休眠：@ManyToOne（fetch=FetchType.LAZY）

我正在将Hibernate与Kotlin一起使用，我在

@manytone

关系上遇到了

FetchType.LAZY

问题。考虑如下：

@ManyToOne(fetch = FetchType.LAZY)
open var event: Event?

问题是，当使用

FetchType.LAZY

时，获取的

事件

将属于类

Event\u$$\ uvst\u……

，其上带有

JavaassistLazyInitializer

。但事件永远不会被初始化，所有内容都将为null或空

删除

FetchType.LAZY

后，一切正常

这在Java中没有发生

我试图在

var

上添加

open

，以便可以正确代理

事件。没有效果

所有的

@实体

类当然也都是

打开的

。如果删除

open

关键字，则不会创建代理，因此不会出现惰性

---

我猜Hibernate不能轻易地代理这些默认的kotlin getter。有办法解决吗？

您可以使用此静态方法来解除实体的代理

/**
 * 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);
}

/**
*尝试正确初始化Hibernate CGLIB的实用程序方法
*代理。
*@param
*@param maybeProxy——可能由Hibernate生成的代理
*@param baseClass--要强制转换到的结果类。
*@返回类的对象
*@ClassCastException
*/
公共静态T deproxy（对象可能是代理，类基类）抛出ClassCastException{
if（可能是HibernateProxy的代理实例）{
返回baseClass.cast（（（HibernateProxy）maybeProxy）.getHibernateLazyInitializer（）.getImplementation（））；
}
返回baseClass.cast（maybeProxy）；
}

我写了一个简单的例子来检查您的问题，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})"
    }
}

Lazy

初始化仅在显式获取值后才开始加载字段数据

希望这对你有帮助

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')