奇怪的延迟加载异常(Strange lazy loading exception)

 我有一个基于Spring的webapp，我的问题是在我的代码发生变化之后，我开始得到延迟加载异常。 下面我详细描述一下情况： 
 
 在一开始的时候 
 
 我有一个帐户和Word实体。 一个帐户可以有多个单词，一个Word可以分配给多个帐户。 
 
 Account.class 
 
@ManyToMany(targetEntity = Word.class, fetch = FetchType.LAZY)
@JoinTable(name = "account_word", joinColumns = {@JoinColumn(name="account_id")}, inverseJoinColumns = {@JoinColumn(name="word_id")})
@OrderBy("word")
private List<Word> words;
 
 Word.class 
 
@ManyToMany(targetEntity = Account.class, fetch = FetchType.LAZY, mappedBy = "words")
@JsonIgnore
private List<Account> accounts;
 
 除了每个帐户只能有一个“WordForToday”，它由在Account.class中映射的Word实体表示，如下所示： 
 
@OneToOne
@JoinColumn(name="word_for_today")
private Word wordForToday;
 
 一切都运转正常。 特别是我有一个@Scheduled方法，每天调用一次以更改每个帐户的“WordForToday”： 
 
 WordServiceImpl.class 
 
@Transactional
@Service
public class WordServiceImpl implements WordService {

@Autowired
AccountDao accountDao;

@PersistenceContext
EntityManager entityManager;

@Override
@Scheduled(cron="0 0 0 * * ?")
public void setNewWordsForToday() {
    logger.info("Starting setting new Words For Today");
    List<Account> allAccounts = accountDao.listAccounts();
    for(Account account : allAccounts) {    
        if(hasListAtLeastOneWordWithDefinitionWhichIsNotSetAsWordForToday(account.getWords(), account.getUsername())) {
            account.setWordForToday(getUserRandomWordWithDefinition(account.getUsername()));
            entityManager.persist(account);
        }
    }
    logger.info("Setting new Words For Today ended");
}

@Override
@Transactional
public List<Word> listUserWords(String username) {
    try {
        Account foundAccount = accountDao.findUserByUsername(username);
        List<Word> userWords = foundAccount.getWords();
        userWords.size();
        return userWords;
    } catch (UserNotFoundException unf) {
        logger.error("User not found: " + username, unf.getMessage());
        return Collections.emptyList();
    }
}
}
 
 AccountDaoImpl.class 
 
@Override
public Account findUserByUsername(String username) throws UserNotFoundException {
    CriteriaQuery<Account> c = cb.createQuery(Account.class);
    Root<Account> r = c.from(Account.class);
    try {
        c.select(r).where(cb.equal(r.get("username"), username));
        Account foundAccount = entityManager.createQuery(c).getSingleResult();
        return foundAccount;
    } catch(NoResultException nre){
        throw new UserNotFoundException();
    }
}

@Override
public List<Account> listAccounts() {
    CriteriaQuery<Account> cq = cb.createQuery(Account.class);
    Root<Account> account = cq.from(Account.class);
    cq.select(account);
    TypedQuery<Account> q = entityManager.createQuery(cq);
    List<Account> accounts = q.getResultList();
    return accounts;
}
 
 上面的代码没有延迟加载异常。 懒惰取得正确的词。 
 
 
 那么 
 
 我必须为每个帐户实现单词组，所以我在项目中添加了新的Group实体。 现在除了“WordForToday”没有改变之外，Account和Word之间没有直接关系。 现在一个帐户可以有多个组，并且只能将一个组分配给一个帐户[具有连接表的单向一对多]。 
 
 Account.class 
 
@OneToMany(fetch = FetchType.LAZY)
@JoinTable(name = "account_wordgroup", joinColumns = {@JoinColumn(name="account_id")}, inverseJoinColumns = {@JoinColumn(name="wordgroup_id")})
@OrderBy("name")
private List<Group> groups;
 
 另外，一个组可以有多个单词，一个单词可以分配给许多组。 
 
 Group.class 
 
@ManyToMany(targetEntity = Word.class, fetch = FetchType.EAGER)
@OrderBy(value="word")
@JoinTable(name = "wordgroup_word", joinColumns = {@JoinColumn(name="wordgroup_id")}, inverseJoinColumns = {@JoinColumn(name="word_id")})
private List<Word> words;
 
 Word.class 
 
@ManyToMany(targetEntity = Group.class, fetch = FetchType.LAZY, mappedBy = "words")
@JsonIgnore
private List<Group> groups;
 
 并且使用上述实体的每个CRUD方法都能正常工作。 我只对上面提到的setNewWordsForToday（）方法有问题，现在看起来像这样（我重构了一些代码）： 
 
 WordServiceImpl.class 
 
@Transactional
@Service
public class WordServiceImpl implements WordService {

@Autowired
AccountDao accountDao;

@PersistenceContext
EntityManager entityManager;

@Autowired
GroupService groupService;

@Override
@Scheduled(cron="0 0 0 * * ?")
@Transactional
public void setNewWordsForToday() {
    logger.info("Starting setting new Words For Today");
    List<Account> allAccounts = accountDao.listAccounts();
    for(Account account : allAccounts) {    
        if(hasListAtLeastOneWordWithDefinitionWhichIsNotSetAsWordForToday(listUserWords(account), account)) {
            account.setWordForToday(getUserRandomWordWithDefinition(account));
            entityManager.persist(account);
        }
    }
    logger.info("Setting new Words For Today ended");
}

@Override
@Transactional
public List<Word> listUserWords(Account account) {
    List<Group> userGroups = groupService.listUserGroups(account);
    List<Word> userWords = new ArrayList<Word>();
    for(Group userGroup : userGroups) {
        userWords.addAll(userGroup.getWords());
    }
    return userWords;
}
}
 
 GroupServiceImpl.class 
 
@Transactional
@Service
public class GroupServiceImpl implements GroupService {

@Override
@Transactional
public List<Group> listUserGroups(Account account) {
    List<Group> userGroups = account.getGroups();
    userGroups.size();
    return userGroups;
}
 
 } 
 
 AccountDaoImpl.class没有改变。 现在，当调用@Scheduled方法时，我有这个延迟加载异常： 
 
 ERROR [org.springframework.scheduling.support.MethodInvokingRunnable] - Invocation of method 'setNewWordsForToday' on target class [class pl.net.grodek.snd.service.WordServiceImpl] failed
 org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: pl.net.grodek.snd.model.Account.groups, no session or session was closed
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:394)
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:386)
at org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:126)
at org.hibernate.collection.internal.PersistentBag.size(PersistentBag.java:242)
at pl.net.grodek.snd.service.GroupServiceImpl.listUserGroups(GroupServiceImpl.java:63)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
at $Proxy48.listUserGroups(Unknown Source)
at pl.net.grodek.snd.service.WordServiceImpl.listUserWords(WordServiceImpl.java:83)
at pl.net.grodek.snd.service.WordServiceImpl.setNewWordsForToday(WordServiceImpl.java:333)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:273)
at org.springframework.scheduling.support.MethodInvokingRunnable.run(MethodInvokingRunnable.java:65)
at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:51)
at org.springframework.scheduling.concurrent.ReschedulingRunnable.run(ReschedulingRunnable.java:81)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:98)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:206)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
 
 我想我尝试了一切，我不知道该怎么做。 它现在阻挡了我几天所以请任何人帮我这个:( 
 
 PS：我当然正在使用OpenEntityManagerInViewFilter。 

I have a Spring-based webapp and my problem is after a change in my code I started to get lazy loading exception. Below I describe the situation in details:
 
In the beginning 
 
I had an Account and Word entities. One account can have many words and one Word can be assigned to many Accounts. 
 
Account.class
 
@ManyToMany(targetEntity = Word.class, fetch = FetchType.LAZY)
@JoinTable(name = "account_word", joinColumns = {@JoinColumn(name="account_id")}, inverseJoinColumns = {@JoinColumn(name="word_id")})
@OrderBy("word")
private List<Word> words;
 
Word.class
 
@ManyToMany(targetEntity = Account.class, fetch = FetchType.LAZY, mappedBy = "words")
@JsonIgnore
private List<Account> accounts;
 
Except that every Account can have only one "WordForToday" which was represented by Word entity mapped in Account.class like this:
 
@OneToOne
@JoinColumn(name="word_for_today")
private Word wordForToday;
 
Everything was working properly. In particular I had a @Scheduled method which was invoked once a day to change the "WordForToday" for every Account:
 
WordServiceImpl.class
 
@Transactional
@Service
public class WordServiceImpl implements WordService {

@Autowired
AccountDao accountDao;

@PersistenceContext
EntityManager entityManager;

@Override
@Scheduled(cron="0 0 0 * * ?")
public void setNewWordsForToday() {
    logger.info("Starting setting new Words For Today");
    List<Account> allAccounts = accountDao.listAccounts();
    for(Account account : allAccounts) {    
        if(hasListAtLeastOneWordWithDefinitionWhichIsNotSetAsWordForToday(account.getWords(), account.getUsername())) {
            account.setWordForToday(getUserRandomWordWithDefinition(account.getUsername()));
            entityManager.persist(account);
        }
    }
    logger.info("Setting new Words For Today ended");
}

@Override
@Transactional
public List<Word> listUserWords(String username) {
    try {
        Account foundAccount = accountDao.findUserByUsername(username);
        List<Word> userWords = foundAccount.getWords();
        userWords.size();
        return userWords;
    } catch (UserNotFoundException unf) {
        logger.error("User not found: " + username, unf.getMessage());
        return Collections.emptyList();
    }
}
}
 
AccountDaoImpl.class
 
@Override
public Account findUserByUsername(String username) throws UserNotFoundException {
    CriteriaQuery<Account> c = cb.createQuery(Account.class);
    Root<Account> r = c.from(Account.class);
    try {
        c.select(r).where(cb.equal(r.get("username"), username));
        Account foundAccount = entityManager.createQuery(c).getSingleResult();
        return foundAccount;
    } catch(NoResultException nre){
        throw new UserNotFoundException();
    }
}

@Override
public List<Account> listAccounts() {
    CriteriaQuery<Account> cq = cb.createQuery(Account.class);
    Root<Account> account = cq.from(Account.class);
    cq.select(account);
    TypedQuery<Account> q = entityManager.createQuery(cq);
    List<Account> accounts = q.getResultList();
    return accounts;
}
 
And this code above was without lazy loading exception. Words where lazy fetched properly. 
 
 
So then
 
I had to implement Groups of Words for every Account, so I added new Group entity in my project. Now there is no direct relationship between Account and Word except "WordForToday" which didn't changed. Now one Account can have many Groups and only one Group can be assigned to one Account [unidirectional one-to-many with join table]. 
 
Account.class
 
@OneToMany(fetch = FetchType.LAZY)
@JoinTable(name = "account_wordgroup", joinColumns = {@JoinColumn(name="account_id")}, inverseJoinColumns = {@JoinColumn(name="wordgroup_id")})
@OrderBy("name")
private List<Group> groups;
 
Additionally one Group can have many words and one Word can be assigned to many groups.
 
Group.class
 
@ManyToMany(targetEntity = Word.class, fetch = FetchType.EAGER)
@OrderBy(value="word")
@JoinTable(name = "wordgroup_word", joinColumns = {@JoinColumn(name="wordgroup_id")}, inverseJoinColumns = {@JoinColumn(name="word_id")})
private List<Word> words;
 
Word.class
 
@ManyToMany(targetEntity = Group.class, fetch = FetchType.LAZY, mappedBy = "words")
@JsonIgnore
private List<Group> groups;
 
And every CRUD methods which use this Entities above are working properly. I only have problem with setNewWordsForToday() method mentioned above which now looks like this (I refactored code a bit):
 
WordServiceImpl.class
 
@Transactional
@Service
public class WordServiceImpl implements WordService {

@Autowired
AccountDao accountDao;

@PersistenceContext
EntityManager entityManager;

@Autowired
GroupService groupService;

@Override
@Scheduled(cron="0 0 0 * * ?")
@Transactional
public void setNewWordsForToday() {
    logger.info("Starting setting new Words For Today");
    List<Account> allAccounts = accountDao.listAccounts();
    for(Account account : allAccounts) {    
        if(hasListAtLeastOneWordWithDefinitionWhichIsNotSetAsWordForToday(listUserWords(account), account)) {
            account.setWordForToday(getUserRandomWordWithDefinition(account));
            entityManager.persist(account);
        }
    }
    logger.info("Setting new Words For Today ended");
}

@Override
@Transactional
public List<Word> listUserWords(Account account) {
    List<Group> userGroups = groupService.listUserGroups(account);
    List<Word> userWords = new ArrayList<Word>();
    for(Group userGroup : userGroups) {
        userWords.addAll(userGroup.getWords());
    }
    return userWords;
}
}
 
GroupServiceImpl.class
 
@Transactional
@Service
public class GroupServiceImpl implements GroupService {

@Override
@Transactional
public List<Group> listUserGroups(Account account) {
    List<Group> userGroups = account.getGroups();
    userGroups.size();
    return userGroups;
}
 
}
 
AccountDaoImpl.class didn't change. And Now i have this lazy loading exception when @Scheduled method is invoked:
 
 ERROR [org.springframework.scheduling.support.MethodInvokingRunnable] - Invocation of method 'setNewWordsForToday' on target class [class pl.net.grodek.snd.service.WordServiceImpl] failed
 org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: pl.net.grodek.snd.model.Account.groups, no session or session was closed
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:394)
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:386)
at org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:126)
at org.hibernate.collection.internal.PersistentBag.size(PersistentBag.java:242)
at pl.net.grodek.snd.service.GroupServiceImpl.listUserGroups(GroupServiceImpl.java:63)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
at $Proxy48.listUserGroups(Unknown Source)
at pl.net.grodek.snd.service.WordServiceImpl.listUserWords(WordServiceImpl.java:83)
at pl.net.grodek.snd.service.WordServiceImpl.setNewWordsForToday(WordServiceImpl.java:333)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:273)
at org.springframework.scheduling.support.MethodInvokingRunnable.run(MethodInvokingRunnable.java:65)
at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:51)
at org.springframework.scheduling.concurrent.ReschedulingRunnable.run(ReschedulingRunnable.java:81)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:98)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:206)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
 
I think that i tried everything and I have no more idea what to do. It is blocking me for a couple of days for now so please anyone help me with this :(
 
PS: I am using OpenEntityManagerInViewFilter of course.

原文：