Question

您好我正在使用@ManyToOne Annotation进行实体映射。

下面的

是我的实体，它们之间有许多关联

student.java

@Entity
@Table(name = "student")
public class student{

    @Id
    @Column(name = "UserID")
    private String userid;

    @ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.EAGER)
    @JoinColumns({
       @JoinColumn(name = "userrole1", referencedColumnName = "VALUE"),
       @JoinColumn(name = "userrole2", referencedColumnName = "DESCRIPTION")

    })
    private studentdetails1 userrole1;

    @ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.EAGER)
    @JoinColumns({
       @JoinColumn(name = "userrole1", referencedColumnName = "VALUE",insertable=false, updatable=false),
       @JoinColumn(name = "userrole2", referencedColumnName = "DESCRIPTION", insertable=false, updatable=false)

    })
    private studentdetails2 userrole2;

//setters and getters 
//constructor

}

studentdetails1.java

@Data
@Entity
@Table(name = "student_details1")
public class studentdetails1 {

    @Id
    @Column(name = "VALUE")
    private String value;

    @Id
    @Column(name = "DESCRIPTION")
    private String description;

   //setters and getters 
   //constructor
}

studentdetails2.java

@Data
@Entity
@Table(name = "student_details2")
public class studentdetails2 {

    @Id
    @Column(name = "VALUE")
    private String value;

    @Id
    @Column(name = "DESCRIPTION")
    private String description;

   //setters and getters 
   //constructor
}

appmain.java

public static void main()
{

//session configuration
     StudentDetails1  sd1 = new StudentDetails1();
            sd1.setValue("abc");
            sd1.setDescription("abcdef");
        StudentDetails2  sd2 = new StudentDetails2();
            sd2.setValue("abcd");
            sd2.setDescription("abcdefd");

            Student student1 = new Student();
            student1.setUserid("1");
            student1.setUserrole1(sd1);
            student1.setUserrole2(sd2);

            Student student2 = new Student();
            student2.setUserid("2");
            student2.setUserrole1(sd1);
            student2.setUserrole2(sd2);
        session.save(student1 );
        session.save(student2 );

        Student con = (Student ) session.get(Student .class,
                        String.valueOf(1));
        System.out.println(con.getUserid());
    }

获取以下行的错误

student con = (student ) session.get(student .class,
                    String.valueOf(1));

我正在使用EAGER FETCH TYPE，当我保存数据时我可以保存并使用SESSION.GET检索数据但是当我评论session.save方法时，即使数据库中有这些表的值，我也是低于错误

org.hibernate.ObjectNotFoundException: No row with the given identifier exists: [com.studentdetails2e#studentdetails2(value=1, description=null)]

at org.hibernate.impl.SessionFactoryImpl$2.handleEntityNotFound(SessionFactoryImpl.java:447)
at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:233)
at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:285)
at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:152)
at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:1080)
at org.hibernate.impl.SessionImpl.internalLoad(SessionImpl.java:1028)
at org.hibernate.type.EntityType.resolveIdentifier(EntityType.java:623)
at org.hibernate.type.EntityType.resolve(EntityType.java:431)
at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:140)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:898)
at org.hibernate.loader.Loader.doQuery(Loader.java:773)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:270)
at org.hibernate.loader.Loader.loadEntity(Loader.java:1933)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:86)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:76)
at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3270)
at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:496)
at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:477)
at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:227)
at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:285)
at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:152)
at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:1080)
at org.hibernate.impl.SessionImpl.get(SessionImpl.java:997)
at org.hibernate.impl.SessionImpl.get(SessionImpl.java:990)
at com.softsol.test.ActvDayRangeRlTest.AccountValid(ActvDayRangeRlTest.java:74)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

我试图解决这个问题，但它显示出同样的错误。

请建议我如何解决这个问题

Answer 1

从stacktrace开始，它表示hibernate加载了Student实体，当它试图加载StudentDetail实体时，它无法在匹配该复合主键的数据库表中找到记录。

根据堆栈跟踪，我猜问题是这样的：

您在Student表中有一条记录，主键值为1，外键值为userrole1=1和userrole2=null。因此，当您尝试使用hibernate从1表中获取id为Student的记录时，并且获取策略为EAGER，那么它会尝试在Student_Detail表中查找记录复合主键为VALUE=1和DESCRIPTION=null但是hibernate无法找到它并抛出异常说：

No row with the given identifier exists: [com.studentdetails2e#studentdetails(value=1, description=null)]

因此，请检查Student表中的数据库数据，主键为1，外键映射应该不正确。我再次猜测在DB端，表之间没有任何外键关系，因为如果是这种情况，那么DB将不允许不正确的FKeys。

<强>更新

当您使用LAZY进行映射并尝试获取Student的记录时，hibernate将为集合元素分配代理，即StudentDetail。当您尝试访问此集合元素时，只有hibernate将访问数据库以获取StiudentDetail的记录。

如果加载EAGER，当你尝试获取Student的记录时，那么hibernate本身会尝试获取映射StudentDetail实体，因此你在使用{{{{{ 1}}但不适用于EAGER抓取。

Answer 2

以我为例，所有注释均正确无误，但在数据库中，table A fk---> table B之间缺少FK，因此表A中存在一行值为b的行。在表B中不存在（此错误应在迁移中检测到）。

该异常可能使您的注意力从实际问题中转移出来，它“找不到行xxx'，因此无法恢复Entity X，但是问题可能是其他任何实体（作为X的属性），例如X#user或X#person

没有给定标识符的行存在hibernate

2 个答案: