懒惰获取的一对一关系

Question

In our java application we have two entities: A main account and the settings for this account. We use hibernate for providing persistence. We want the account settings to be lazy loaded. So we did this:

AccountMain:

@OneToOne(optional = false, cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true)
private AccountMainSettings        accountMainSettings;

@JoinColumn(name = AccountMainSettings.ACCOUNT_MAIN_SETTINGS_ID, unique = true, nullable = false, updatable = false, insertable = true)
public final AccountMainSettings getAccountMainSettings() {
return this.accountMainSettings;
}

AccountMainSettings:

@OneToOne(mappedBy = "accountMainSettings")
private AccountMain        accountMain;

public final AccountMain getAccountMain() {
return this.accountMain;
}

When we load the AccountMainSettings object in AccountMain it is proxied as it should be. But when we call a method of AccountMainSettings, the object is not loaded from the database an an NPE is thown of course. Having read Making-a-onetoone-relation-lazy didn't help much. We neither have a nullable association nor do we want to convert it to a ManyToOne association. When we switch to eager loading the problem is "solved", as the settings are loaded but they contain many fields so we don't want them to be unnecessarily loaded.

How can we implement lazy loading in this context?

Update: Here our jUnit Test:

@Test
public final void getMainAccountByAccountId() {
final AccountMain accountMain = this.accountMainDAO.getMainAccountByAccountId(PersistTestCaseConstants.SAVED_MAIN_ACCOUNT_ID);
final AccountMainSettings accountMainSettings = accountMain.getAccountMainSettings();
final String imprint = accountMainSettings.getImprint();
assertEquals(PersistTestCaseConstants.OBJECT_SUCESSFUL_ADDED, imprint.length(), 1000);
}

And the Stacktrace:

java.lang.NullPointerException
                at com.persolog.eport.service.dao.AccountMainDAOTest.getMainAccountByAccountId(AccountMainDAOTest.java:418)
                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:45)
                at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
                at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
                at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
                at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
                at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
                at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
                at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231)
                at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
                at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
                at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
                at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
                at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
                at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
                at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
                at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
                at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
                at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174)
                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:467)
                at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
                at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
                at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Answer 1

Getter shouldn't be final. And use @JoinColumn annotation on field, not on getter. Or use all mapping for getter, then you should add @Access(AccessType.PROPERTY)

Answer 2

I have this and it works for me in my code.

@JoinColumn(name = "contract_id", referencedColumnName = "id")
@OneToOne(fetch = FetchType.LAZY)
private Contract contract;

Are you missing the referencedColumnName in your code? you are specifying the name of the join column but not the name of the column on the other side of the relationship

Note all my annotations are on the field and my getter and setter are just plain old getters and setters in this class