从投影列表获取子实体时出现间歇性惰性异常

Question

In my spring project, I'm getting lazy intialization exception intermittently when i try to fetch the child entity from the object got via projection list in dao layer

    public class TestMapping extends PersistentEntity {

    private static final long serialVersionUID = 1L;

    private TestModel testModel = new TestModel();

    private String testMappingString;

    private String testModelCategory;

    private Boolean active;

    }

<hibernate-mapping>
    <class name="com.domain.TestModel"
        dynamic-insert="true" dynamic-update="true"
        table="ref_manufacturermodel">

        <id name="id" column="testmodelid" type="long"
            unsaved-value="-1">
            <generator class="seqhilo">
                <param name="max_lo">1</param>
                <param name="sequence">
                    testmodel_seq
                </param>
            </generator>
        </id>

        <version name="version" column="version"
            type="java.lang.Integer" unsaved-value="null" />

        <component name="auditInfo"
            class="com.domain.AuditInfo">

            <many-to-one name="createdBy"
                class="com.domain.User" cascade="none" outer-join="auto"
                update="false" insert="true" 
                column="createdby" not-null="true" />

            <property name="createdDate" type="java.util.Date"
                update="false" insert="true" column="createddate" not-null="true" />

            <property name="lastUpdatedDate" type="java.util.Date"
                update="true" insert="true" column="lastupdateddate" />

            <many-to-one name="updatedBy"
                class="com.domain.User" cascade="none" outer-join="auto"
                update="true" insert="true" 
                column="updatedby" />

        </component>

        <property name="modelNumber" type="java.lang.String"
            update="true" insert="true" column="modelnumber" not-null="true" />

        <property name="modelTitle"
            type="com.hibernate.userType.LabelUserType" update="true"
            insert="true" column="title" />

        <property name="modelCode" type="java.lang.String"
          update="true" insert="true" column="modelcode"/>

        <property name="active" type="java.lang.Boolean" not-null="true"
            update="true" insert="true" column="active" />

        <many-to-one name="model" class="com.domain.Model"
            cascade="none" update="true" insert="true" foreign-key="fk_model_modelid"
            column="modelid" />  

        .................................................
        .................................................
        .................................................

    </class>    

</hibernate-mapping>


    public class TestModel extends PersistentEntity {


     private Model model;
     ........
     ........//Number of child objects

    }


    public interface TestModelDAO extends DAO<TestModel, Long> {
       public List<TestModel> findTestModelByMapping(String testString, String tester,String testModelCategory);
    }

    public class TestModelDaoImpl extends BaseDAOImpl<TestModel, Long> implements TestModelDAO {
    @Override
    public List<TestModel> findTestModelByMapping(String testString, String tester,String testModelCategory) {
        DetachedCriteria dc = DetachedCriteria.forClass(TestMapping.class);
        dc.setProjection(Projections.property("testModel"));
        dc.createAlias("testModel", "tm");
        dc.createAlias("tm.categorytester", "cm");
        dc.createAlias("cm.category", "category");
        dc.add(Restrictions.sqlRestriction("lower(testString) in (?)", testString.toLowerCase(),
                Hibernate.STRING));
        dc.add(Restrictions.eq("testModelCategory", testModelCategory));
        return getHibernateTemplate().findByCriteria(dc);
    }
    }


    public interface TestMappingService {
        public ManufacturerModel getMappedModels();
    }


    @Service("testMappingService")
    public class TestMappingServiceImpl implements TestMappingService {
       public ManufacturerModel getMappedModels() {
        ......................
        ......................
        List<TestModel> modelList=testModelDao.findTestModelByMapping("abc", "test1", "category1");
        TestModel testModel = modelList.size()>0?modelList.get(0):null;
        Workflow workflow = testModel.getModel().getWorkflow;
        **// When i put debugger point on testmodel object it shows me the com.sun.jdi.InvocationException on the child entity *Model*. So as soon as getWorkflow is called, lazy exception is thrown. ** 
       }
    }

1. In one of my service class, i am getting the List The above method returns me the list of TestModel and when i try to access the child objects of the TestModel then i got the lazy initialization exception in the logs.

2. When i debug the code and mouse over the TestModel object, the debugger popup displays the com.sun.jdi.InvocationException for child objects of the TestModel object.

3. I don't get this exception every time. Some times its displaying

Not sure why we are seeing such a weired behavior. Why the lazy exception is displaying for the child oject? Any suggestions?

Answer 1

The default thing for Hibernate to do is being lazy, and not load child objects, but only do that when needed.

But for this to work the parent object has to be in persisted state, with an active persistent context.

You are making a detached query, and therefore the parent is in detached state.

You need to have get a Criteria from the Session object.

Answer 2

Is your method ,which is manipulating the objects returned from DAO, running in a transaction. If not you can try using @Transactional on the method of getMappedModels() TestMappingService interface , see if that solves your problem.