Spring 4 Hibernate 4 JPA LazyInitializationException：无法延迟初始化角色集合

Question

I made a database connection with spring 4 used with hibernate 4 and JPA. When I try to get a lazy initializated field I got an LazyInitializationException.

My applicationContext.xml:

<context:annotation-config />
<context:component-scan base-package="xy" />

<jpa:repositories base-package="xy.repositories" />

<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />
<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="persistenceUnitName" value="punit" />
    <property name="dataSource" ref="dataSource" />

    <property name="jpaVendorAdapter">
        <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <property name="showSql" value="true" />
        </bean>
    </property>
    <property name="jpaPropertyMap">
        <map>
            <entry key="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect" />
            <entry key="hibernate.hbm2ddl.auto" value="update" />
            <entry key="hibernate.format_sql" value="true" />
        </map>
    </property>
</bean>

<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="entityManagerFactory" />

</bean>


<tx:annotation-driven transaction-manager="transactionManager" proxy-target-class="true" />

<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver" />
    <property name="url" value="jdbc:mysql://localhost:3306/keysystem" />
    <property name="username" value="username" />
    <property name="password" value="password" />
</bean>

<bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"/>

Model:

@Entity
@Table
public class Employee {
    @Id
    @GeneratedValue
    private long employeeId;
    private String firstName;
    private String lastName;
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "employee")
    @Cascade(CascadeType.ALL)
    @Fetch(FetchMode.SELECT)
    private Set<Legitimacy> legitimacies;
    ...

I found only MVC filter solution, but I don't use MVC. I tried Hibernate.initialize(...) and @Transational, @Fetch annotations but these didn't solved my problem.

Here is the stacktrace:

Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: xy.Employee.legitimacies, could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:575)
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:214)
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:554)
    at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:142)
    at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:180)
    ... 64 more

Answer 1

Guillaume is right, you are using a proxy managed by Hibernate in some location in your code which is outside a transactional context.

Because of that, when you call getLegitimacies() that has not been initialized yet, Hibernate try to populate its proxy by graping a session and make a database call.

If you are in a controller for example and no session is available, an exception is thrown. You have to fetch your legitimacies set at some point in your dao (by using FETCH keyword in your HQL query for example) :

FROM Employee e LEFT JOIN FETCH e.legitimacies WHERE <your_predicate>;

You should also not manipulate your entities if not in service/dao layer but use a DTO instead to avoid those problems.

Answer 2

Lazy exceptions occurs when you try to access a referenced object outside of the original session.

Basically, you are doing this :

* Open a session
* Fetch an object, let's say X
* Close the session
* Try to access X.getY()

A solution is to fetch X and Y at the same time, while the session is open.