Hibernate:org.hibernate.LazyInitializationException:无法初始化代理 - 没有Session

Question

对数据库有以下查询:

        Session session = EmployeesDAO.getSessionFactory().getCurrentSession();
        List<Employee> employees = new ArrayList<Employee>();
        try {
            session.beginTransaction();
            String hqlQuery = "from Employee emp "
                    + "left join fetch emp.employeesOffices employeesOffice "
                    + "left join fetch employeesOffice.office employeesOfficeOffice "
                    + "left join fetch employeesOfficeOffice.company "
                    + "left join fetch emp.address empAddress "
                    + "left join fetch empAddress.city empAddressCity "
                    + "left join fetch empAddressCity.country";
            Query empQuery = session.createQuery(hqlQuery);
            empQuery.setMaxResults(maxResult);
            employees = (List<Employee>) empQuery.list();
            session.getTransaction().commit();

        } catch (HibernateException e) {
            session.getTransaction().rollback();
            e.printStackTrace();
        }

在获取employee.address.street,employee.address.houseNumber或employee.address.city时,它失败并出现异常:

org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:164)
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:285)
    at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
    at com.employees.model.Address_$$_javassist_6.getCity(Address_$$_javassist_6.java)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:87)
    at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:67)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:169)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
    at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:985)
    at org.apache.jsp.WEB_002dINF.listEmployees_jsp._jspx_meth_c_005fout_005f3(listEmployees_jsp.java:306)
    at org.apache.jsp.WEB_002dINF.listEmployees_jsp._jspx_meth_c_005fforEach_005f1(listEmployees_jsp.java:248)
    at org.apache.jsp.WEB_002dINF.listEmployees_jsp._jspx_meth_c_005fforEach_005f0(listEmployees_jsp.java:155)
    at org.apache.jsp.WEB_002dINF.listEmployees_jsp._jspService(listEmployees_jsp.java:89)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:690)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:477)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:402)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:329)
    at com.employees.controller.EmployeeController.processRequest(EmployeeController.java:69)
    at com.employees.controller.EmployeeController.doGet(EmployeeController.java:30)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1001)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

员工映射:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.employees.model.Employee" table="employees">
        <id column="employee_id" name="employeeId" type="int">
            <generator class="sequence">
                <param name="sequence">EMP_SEQ</param>
            </generator>
        </id>
        <property column="first_name" name="firstName" type="java.lang.String" />
        <property column="last_name" name="lastName" type="java.lang.String" />

        <many-to-one name="address" column="address_id" 
            class="com.employees.model.Address"/>
        <set name="employeesOffices" >
            <key column="employee_id" />
            <one-to-many class="com.employees.model.EmployeeOffice"/>
        </set>

    </class>
</hibernate-mapping>

地址映射:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.employees.model.Address" table="addresses">
        <id column="address_id" name="addressId" type="int">
            <generator class="sequence">
                <param name="sequence">ADDRESS_SEQ</param>
            </generator>
        </id>
        <property column="street" name="street" type="java.lang.String" />
        <property column="house_number" name="houseNumber" type="int" />
        <many-to-one name="city" column="city_id"
            class="com.employees.model.City"/>
    </class>

</hibernate-mapping>

其他课程(办公室,公司等)绝对正常.如果注释在jsp应用程序中加载地址字段的行没有任何例外.怎么了？顺便说一下,它显示了有关jsp的所有信息,尽管有例外.

Answer 1

您的对象内部employee已lazy初始化.这意味着,他们只是根据非封闭会话的需求进行初始化.所以你必须在从DB获取之后在循环内手动初始化它们:

Query empQuery = session.createQuery(hqlQuery);
empQuery.setMaxResults(maxResult);
employees = (List<Employee>) empQuery.list();
for (Employee emp : employees) {
    Hibernate.initialize(emp.address);
}

Answer 2

Sinche Hibernate 4.2你可以使用

.setProperty("hibernate.enable_lazy_load_no_trans", "true");

这个选项解决了可怕的问题

org.hibernate.LazyInitializationException: could not initialize proxy -
no Session

这花了很多时间让程序员离开.

Answer 3

与映射无关.当你在一个对象上提供延迟加载时,你接受了一个让ORM世界迷惑了十年的责任:你加载对象的会话将与发出延迟请求时出现的会话相同.

在您的情况下,看起来会话已完全消失.

您必须有一些方法来维护会话(这通常会导致需要会话范围,这意味着Seam或CDI(在EE 6中))或者您必须使用您拥有的新会话重新同步对象(通常再看一遍).