Springboot - 如何保存多对多关系数据

Question

嗨，我有一个角色表和一个权限表，它们具有多对多的关系。 我已经创建了下面链接中提到的实体

https://www.baeldung.com/jpa-many-to-many

角色实体

@Entity
@Table(name="role")
@NamedQuery(name="Role.findAll", query="SELECT r FROM Role r")
public class Role implements Serializable {

    @ManyToMany
    @JoinTable(name="role_permission", joinColumns=@JoinColumn(name="role_id"),inverseJoinColumns=@JoinColumn(name="permission_id"))
    private Set<Permission> permissions = new HashSet<>();
}

权限实体

@Entity
@Table(name="permission")
@NamedQuery(name="Permission.findAll", query="SELECT p FROM Permission p")
public class Permission implements Serializable {

    @ManyToMany(mappedBy="permissions")
    private Set<Role> roles = new HashSet<>();
}

我已经为每个实体创建了 JPA 存储库，并且正在尝试将权限保存到角色。 我已经在表中有一组权限/列表，我正在尝试将它们 map 分配给某个角色。我正在尝试使用 Spring Z9CE3D1BD8890F16A0C448093595087C6 存储库执行以下代码。

        Role r = new Role();
        r.setName("New Admin Role");

        for(int i=1; i<=3; i++) {
            Permission p = permissionCrudRepository.getOne(i);
            r.getPermissions().add(p);
            p.getRoles().add(r);
        }

        roleCrudRepository.save(r);

执行代码时，我得到

org.hibernate.LazyInitializationException：无法初始化代理 [aaa.entity.Permission#1] - 没有 Session

跟踪日志

org.hibernate.LazyInitializationException: could not initialize proxy [aaaa.entity.Permission#1] - no Session
    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:170)
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:310)
    at org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor.intercept(ByteBuddyInterceptor.java:45)
    at org.hibernate.proxy.ProxyConfiguration$InterceptorDispatcher.intercept(ProxyConfiguration.java:95)
    at aaaa.entity.Permission$HibernateProxy$Tm4WEubz.getRoles(Unknown Source)
    at aaaa.UserTests.saveRolePermission(UserTests.java:126)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74)
    at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
    at org.junit.vintage.engine.execution.RunnerExecutor.execute(RunnerExecutor.java:40)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
    at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
    at java.util.Iterator.forEachRemaining(Iterator.java:116)
    at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
    at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
    at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
    at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
    at org.junit.vintage.engine.VintageTestEngine.executeAllChildren(VintageTestEngine.java:80)
    at org.junit.vintage.engine.VintageTestEngine.execute(VintageTestEngine.java:71)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:170)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:154)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:90)
    at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:89)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)

application.properties文件

server.port = 8090
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql = true
spring.datasource.url=jdbc:mysql://localhost:3306/abc
spring.datasource.username=root
spring.datasource.password=root
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialect

知道为什么会出现这个问题，以及我可以采取什么样的行动。

Answer 1

ManyToMany 关系默认是惰性的。

这意味着您对 getRoles() 的调用会进行数据库查询以实际获取角色。

因此，您需要进行交易才能实现这一目标。 注释 @Transactionnal 您的方法，其中包含以下代码以设置事务：

@Transactionnal 
public void yourMethod(){

        [...]

        Role r = new Role();
        r.setName("New Admin Role");

        for(int i=1; i<=3; i++) {
            Permission p = permissionCrudRepository.getOne(i);
            r.getPermissions().add(p);
            p.getRoles().add(r);
        }

        roleCrudRepository.save(r);
}

您也可以将关系设置为获取类型 EAGER，但这通常在性能方面是个坏主意。