Hibernate: org.hibernate.LazyInitializationException: could not initialize proxy - no Session [duplicate]

Question

Have following query to the database:

        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();
        }

While fetching employee.address.street, employee.address.houseNumber or employee.address.city it fails with the exception:

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)

Mapping for Employee:

<?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>

Mapping for Address:

<?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>

It's absolutely normal with other classes (Office, Company, etc). If comment the lines which load address fields in jsp application works without any exceptions. What's wrong? By the way it shows all information on jsp despite the exception.

Snakemouth

off topic: I think it's better to specify package attribute in hibernate-mapping tag, after that you have no need to write full name of classes – Borries

Answer 1

Your objects inside employee are lazy initialized. That's mean, they are initializing only on demand on non-closed session. So you have to initialize them all manually inside loop after fetching from DB:

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

Clodhopper

Then what's the point of lazy? Might as well change the semantics to do an eager fetch. – Rufescent

@Rufescent this is not always needed. Sometimes it is convenient to have lazy initialization, and initialize children only if it is needed. – Clodhopper

that's right, that's why my suggestion is that you get the scoping semantics right for each case. :) – Rufescent

Why are they lazy initialized? Why do Office and other associations work correctly? Is it wrong that left join fetch provides eager fetching? – Snakemouth

for (Employee emp : employees) { Hibernate.initialize(emp.getAddress()); } gives me NullPointerException. – Snakemouth

yes if you specify join fetch all data would be get immediately. look at this topic about fetch strategies mkyong.com/hibernate/hibernate-fetching-strategies-examples – Borries

The point here is that you want the mapping to be lazy by default. This gives you the opportunity to load the data if you know you need it but not if you don't. If you need the data you need the data, you can't get away from that! You can use a join fetch or just access the property before closing the session but either way, you need that data so make sure you load it! – Leatherjacket

@Snakemouth add additionally check for null values: ... { if (emp != null) Hibernate.initialize(emp.getAddress()); } .... It this will not help, then post here full stack trace of this NPE exception. – Clodhopper

Thanks a lot, @Alex and @Andremoniy! You really help me to understand and solve this problem! I'll update my question with the code. – Snakemouth

Answer 2

Sinche Hibernate 4.2 you can use

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

this option solves the dreaded

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

which took so many hours of life to programmers away.

Fabre

Doesn't work for me in Hibernate 4.3.11.Final – Pestle

This did the trick on Hibernate 5.0.11.Final – Lailaibach

Worked for me - Hibernate 4.3.6 Final – Protomorphic

You might read this article before doing this. – Shape

it's anti pattern – Untimely

@zond, It's the only solution that has worked with me, what else shall we do to overcome this problem? – Peignoir

Answer 3

Has nothing to do with the mapping. When you provide for lazy loading on an object, you accept a responsibility that has bewitched the ORM world for a decade: that the session you loaded the object with will be the same one as the session that is present when the lazy requests are issued.

In your case, it looks like the session is completely gone.

You have to have some means of either maintaining the session (which often leads to a need for conversation scope, which would mean either Seam or CDI (in EE 6)) or you have to resync your object with the new session that you have (usually by looking it up again).

Rufescent

Answer 4

add laze=false into <class name="com.employees.model.Employee" table="employees"> or you can init your object in Hibernate.init(Object) when you get object from db

Borries

Thanks but lazy=false doesn't help. I answered about Hibernate.initialize under another answer. It doesn't work too. – Snakemouth

oh. I make mistake. specify lazy=false in <class name="com.employees.model.Employee" table="employees">. This make all fields of Employee class not lazy inicialization – Borries

Properties of all hibernate classes are not lazy by default, associations are loaded through left join fetch. Is it not right? I can't really see any lazy loaded attributes. – Snakemouth

By default all properties lazy. – Borries

but if you set lazy=false to all classes in your mapping it makes fetch join automaticly – Borries