未能懶惰地初始化一個角色的集合，..無法初始化代理 - 沒有會話 - JPA + SPRING

Question

我沿着Spring（3.2.2）使用JPA（與Hibernate 4.3.3一起作爲持久性提供者），我的所有字段加載罰款，但是當我試圖進入我的收藏它拋出的錯誤 -

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) 

當我調試在我的實體類中定義的每個收集這個，我得到錯誤 - com.sun.jdi.InvocationException occurred invoking method.

我試圖用收集.size（）和Hibernate.initialize（），但沒有一個工作。 在互聯網上搜索我發現擴展Persitence將解決問題即。

@PersistenceContext(type=PersistenceContextType.EXTENDED) 

     protected EntityManager em; 

這個工作不錯，但通過這次我發現，EM會一直保持打開，現在春天不會處理這個問題。有沒有什麼辦法可以用Spring來解決這個問題。任何幫助，高度讚賞。

我的實體是爲 -

@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(); 

} 

我的XML配置是 -

<?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> 

通過服務層，這是我的道我打電話道

@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); 
    } 


} 

役層

@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); 
    } 

} 

這是主要

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

像@Zeus說，這之前已經很多很多，時間回答。因爲你的事務開始，併爲您服務呼叫結束您在你的測試類這一問題：從Hibernate文檔

Category parentCategory=serviceCategory.findCategoryById(2l); 

回想一下，延遲加載只有Hibernate的Session內有效（在這種情況下，Hibernate的Session開始，以您的服務電話結束）。你不能重新連接到休眠會話（簡單地）來初始化集合。

我不完全確定你的意思，當你想解決它「春天」。由於這不是春季問題。從本質上來說，解決這個問題的兩種方法是在加載父進程的hibernate會話中加載集合，或者在原始休眠會話之外執行單獨的提取。

Answer 2

的問題是，當這個方法調用返回：

Category parentCategory=serviceCategory.findCategoryById(2l); 

在這裏，你是在一個@Transactional方面不再。這意味着鏈接到parentCategory的會話已關閉。現在當您嘗試訪問鏈接到已關閉會話的集合時，會發生No Session錯誤。

需要注意的一件事是，主要方法在任何spring bean之外運行，並且沒有持久化上下文的概念。

解決方法是從事務性上下文中調用parentCategory.getAllParentCategoryrefs()，該事務永遠不會成爲應用程序的主要方法。

然後將parentCategory重新掛接到新的持久性上下文，然後調用getter。

嘗試例如傳遞parentCategory回相同的服務的一個事務性方法：

serviceCategory.nowItWorks(parentCategory); 

而使用該服務的方法是事務：

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

而在DAO：

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

Answer 3

嘗試使用fetch=FetchType.EAGER，它會工作

Answer 4

你的域集收集使用@Fetch(FetchMode.SELECT)和@LazyCollection(LazyCollectionOption.FALSE)，它會工作