failed to lazily initialize a collection of role,..could not initialize proxy - no Session - JPA + SPRING

Question

I am using JPA(with Hibernate 4.3.3 as persistence provider ) along Spring (3.2.2) , all my fields are loading fine but when I am trying to access my Collection it's throwing the error-

Exception in thread "main" org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.br.common.catalog.entity.Category.allParentCategoryXrefs, could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:572)
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:212)
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:551)
    at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:140)
    at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:526)
    at java.lang.String.valueOf(String.java:2827)
    at java.io.PrintStream.println(PrintStream.java:771)
    at test.Test.main(Test.java:30)

When I debugged this I was getting error for every collection defined in my entity class - com.sun.jdi.InvocationException occurred invoking method.

I tried using collection.size() and Hibernate.initialize() but none of this worked. On searching on internet I found that extending Persitence will solve the problem ie.

 @PersistenceContext(type=PersistenceContextType.EXTENDED)

        protected EntityManager em;

this worked fine but through this I found that em will always remain opened , now spring will not handle this. Is there any way to solve this problem using Spring. Any Help is highly appreciated.

My Entities are as -

  @Entity
    @Inheritance(strategy = InheritanceType.JOINED)
    @Table(name="CATEGORY")
    public class Category implements Serializable {
       @Id
        @GeneratedValue(generator= "CategoryId")
         @Column(name = "CATEGORY_ID")
        protected Long id;

        @ManyToOne(targetEntity = Category.class)
        @JoinColumn(name = "DEFAULT_PARENT_CATEGORY_ID")
        @Index(name="CATEGORY_PARENT_INDEX", columnNames={"DEFAULT_PARENT_CATEGORY_ID"})
        protected Category defaultParentCategory;

        @OneToMany(targetEntity = Categoryref.class, mappedBy = "categoryrefPK.category")
        @Cache(usage = CacheConcurrencyStrategy.READ_WRITE, region="test")
        @OrderBy(value="displayOrder")
        @BatchSize(size = 50)

        protected List<Categoryref> childCategoryRefs = new ArrayList<Categoryref>(10);
        @OneToMany(targetEntity = Categoryref.class, mappedBy = "categoryrefPK.subCategory",fetch=FetchType.LAZY)
        @Cascade(value={org.hibernate.annotations.CascadeType.MERGE, org.hibernate.annotations.CascadeType.PERSIST})
        @OrderBy(value="displayOrder")
        @BatchSize(size = 50)
        protected List<Categoryref> parentCategoryRefs = new ArrayList<Categoryref>(10);

    }


@Entity
@Polymorphism(type = PolymorphismType.EXPLICIT)
@Inheritance(strategy = InheritanceType.JOINED)
@Table(name = "CATEGORY_REF")
public class Categoryref implements Serializable {
    /** The category id. */
    @EmbeddedId
    CategoryrefPK categoryrefPK = new CategoryrefPK();

    public CategoryrefPK getCategoryrefPK() {
        return categoryrefPK;
    }

    public void setCategoryrefPK(final CategoryrefPK categoryrefPK) {
        this.categoryrefPK = categoryrefPK;
    }
  }

@Embeddable
public class CategoryrefPK implements Serializable {

    @ManyToOne(targetEntity = Category.class, optional=false)
    @JoinColumn(name = "CATEGORY_ID")
    protected Category category = new Category();

    @ManyToOne(targetEntity = Category.class, optional=false)
    @JoinColumn(name = "SUB_CATEGORY_ID")
    protected Category subCategory = new Category();

}

My Xml Configuration is as -

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/aop
           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-3.0.xsd
           http://www.springframework.org/schema/tx  
           http://www.springframework.org/schema/tx/spring-tx.xsd">

    <context:component-scan base-package="com.br" />

    <bean id="dataSource"
        class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        ....
    </bean>
<!--  this is also used we can used this also  -->
  <tx:annotation-driven transaction-manager="transactionManager" />  
    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="entityManagerFactory" />
    </bean>
    <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="persistenceXmlLocation" value="classpath:META-INF/persistence.xml" />
        <property name="dataSource" ref="dataSource" />
         <property name="persistenceUnitName" value="abc" />   
        <property name="packagesToScan" value="com.br.common.*" />
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                <property name="showSql" value="true" />
                <property name="databasePlatform" value="org.hibernate.dialect.MySQLDialect" />
            </bean>
        </property>
    </bean>  


</beans>  

Persitence.xml

    <?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
    xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
    <persistence-unit name="abc">
        transaction-type="RESOURCE_LOCAL">
          <mapping-file>META-INF/category.orm.xml</mapping-file>
        <class>com.br.common.Category</class>
        <class>com.br.common.Categoryref</class>
        <class>com.br.common.CategoryrefPK</class>

        <properties>
            <property name="javax.persistence.jdbc.user" value="user"
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"></property>
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/test>
            <property name="javax.persistence.jdbc.password" value="...">
            <property name="hibernate.show_sql" value="true" />

            <property name="hibernate.transaction.flush_before_completion"
                value="false" />
            <property name="hibernate.connection.autocommit" value="true" />
            <property name="hibernate.cache.region.factory_class" value="org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory"/>
            <property name="hibernate.cache.use_second_level_cache" value="true" /> 
            <property name="hibernate.cache.use_query_cache" value="true"/>
            <property name="hibernate.generate_statistics" value="false" />
            <property name="hibernate.archive.autodetection" value="false" />
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" />
            <property name="hibernate.id.new_generator_mappings" value="true" />
        </properties>
    </persistence-unit>
</persistence>

this is my dao i am calling dao through service layer

@Repository("categoryDaoImpl")
public class CategoryDaoImpl implements ICategoryDAO {

    @PersistenceContext
    protected EntityManager em;


    public Category save(Category category) {
      Category category2=   em.merge(category);

         em.flush();
         return category2;
  }
    public Category readCategoryById(Long categoryId) {
        return em.find(Category.class, categoryId);
    }


}

servie layer

    @Service("blCatalogService")
@Transactional(propagation=Propagation.REQUIRED)
public class CatalogServiceImpl implements ICatalogService {

    @Resource(name="categoryDaoImpl")
    protected ICategoryDAO categoryDao;

    @Transactional
    public Product saveProduct(Product product) {
        return productDao.save(product);
    }

    public Category findCategoryById(Long categoryId) {
        return categoryDao.readCategoryById(categoryId);
    }

}

this is main

public class Test {


        public static void main(String[] args) {
                ApplicationContext context = new ClassPathXmlApplicationContext(
                    "applicationContext-persistence.xml");
            ICatalogService serviceCategory= (ICatalogService) context
                    .getBean("blCatalogService");
                Category parentCategory=serviceCategory.findCategoryById(2l);
    System.out.println(parentCategory.getAllParentCategoryrefs());//here error is coming while accessing collection
    }
    }

Answer 1

The problem is that when this method call returns:

Category parentCategory=serviceCategory.findCategoryById(2l);

Here you are no longer in a @Transactional context. this means that the session linked to parentCategory got closed. now when you try to access a collection linked to a closed session, the No Session error occurs.

One thing to notice is that the main method runs outside any spring bean and has no notion of persistence context.

The solution is to call the parentCategory.getAllParentCategoryrefs() from a transactional context, which can never be the main method of your application.

Then reattach the parentCategory to the new persistence context, and then call the getter.

Try for example to pass the parentCategory back to a transactional method of the same service:

serviceCategory.nowItWorks(parentCategory);

where the method on the service is transactional:

@Transactional(readOnly=true)
public void nowItWorks(Category category) {
    dao.nowItWorks(category);
}

And in the DAO:

public void nowItWorks(Category category) {
    Category reattached = em.merge(category);
    System.out.println("It works: " + reattached.getAllParentCategoryrefs());
}