休眠多对一渴望获取不工作 [英] Hibernate many to one eager fetching not working

问题描述

我正在尝试使用休眠注释从数据库中获取数据，但是它没有按我的预期工作.我有两个表Employee和Department. Java代码如下:

I am trying to fetch data from database using hibernate annotation but it is not working as my expected. I have a two table Employee and Department. the java code is as below :

员工类别

 @Entity
    @Table(name = "EMPLOYEE")        
    public class EmployeeBO {

        @Id
        @GeneratedValue(strategy=GenerationType.IDENTITY)
        @Column(name = "EMPID")
        private int empId;
        @Column(name = "EMPNAME")
        private String empName;
        @Column(name = "SALARY")
        private int empSalary;
        @Column(name = "EMPADDRESS")
        private String empAddress;
        @Column(name = "EMPAGE")
        private int empAge;
        @Column(name = "DEPTID")
        private Integer deptId; 
        @ManyToOne(fetch=FetchType.EAGER)
        @JoinColumn(name="DEPTID", nullable = true, insertable = false, updatable = false)
        private DepartmentBO departmentBO;
// getter and setter 
    }

部门课程:

@Entity
@Table(name = "DEPARTMENT")
public class DepartmentBO {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name = "DEPTID")
    private int deptid;

    @Column(name = "DEPTNAME")
    private String deptName;
   // getter and setter.
}

spring-servlet.xml文件:

spring-servlet.xml file :

<?xml version="1.0" encoding="UTF-8"?>
<!--?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:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:mvc="http://www.springframework.org/schema/mvc" 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/context http://www.springframework.org/schema/context/spring-context-3.0.xsd 
    http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">


    <context:annotation-config></context:annotation-config>

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

    <context:property-placeholder location="file:D:/EasyProp/db.properties" ignore-unresolvable="false"/>

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">  
        <property name="prefix" value="/WEB-INF/jsp/" />  
        <property name="suffix" value=".jsp" />  
    </bean>

    <bean id="basicDataSource" 
         class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> 

        <property name="driverClassName" value="${driver.classname}" />
        <property name="url" value="${driver.url}" />
        <property name="username" value="${username}" />
        <property name="password" value="${password}" />
<!--        <property name="initialSize" value="10"/> -->
<!--         <property name="maxActive"  value="25"/> -->
<!--         <property name="maxIdle" value="25"/>   -->
        <!-- <aop:scoped-proxy/> -->
    </bean> 
    <tx:annotation-driven />
    <bean id="transactionManager"
        class="org.springframework.orm.hibernate3.HibernateTransactionManager">
        <property name="sessionFactory" ref="mySessionFactory" />
    </bean>

    <!-- <bean id="dbUtil" class="com.web.utility.OnLoadStartUp" init-method="initialize">
        <property name="dataSource" ref="basicDataSource" />
    </bean> -->

    <!-- <bean id="loadOnStartUp" class="com.web.utility.LoadOnStartUp">
        <property name="baseService" ref="baseService"></property>
    </bean> -->

    <bean id="mySessionFactory"
        class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
        <property name="dataSource" ref="basicDataSource" />
        <property name="annotatedClasses">
            <list>
                <value>com.web.bo.EmployeeBO</value>
                <value>com.web.bo.DepartmentBO</value>  
            </list>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</prop>
                <prop key="hibernate.show_sql">true</prop>
                <prop key="hibernate.hmb2ddl.auto">validate</prop>
                <prop key="hibernate.generate_statistics">true</prop>
                <prop key="hibernate.jdbc.fetch_size">10</prop>
                <prop key="hibernate.jdbc.batch_size">25</prop>
                <prop key="hibernate.jdbc.batch_versioned_data">true</prop>
                <prop key="hibernate.max_fetch_depth">3</prop>
                <prop key="hibernate.default_batch_fetch_size">8</prop>
                <prop key="hibernate.order_updates">true</prop>
                <prop key="hibernate.connection.release_mode">on_close</prop>
                <prop key="hibernate.bytecode.use_reflection_optimizer">true</prop>
                <prop key="hibernate.bytecode.provider">javassist</prop>                
            </props>
        </property>
    </bean>
</beans>

当我尝试从employee和department表中获取所有数据，但它仅从employee表中返回数据时，我的命中hql查询代码如下:

when i trying to fetch all data from employee and department table but it only returns the data from employee table my code for hit hql query as below :

List<EmployeeBO> empList = null; 
        empList = sessionFactory.getCurrentSession().createQuery("From "+employeeBO.getClass().getName()).list();   

上面的查询在数据库中命中如下.

above query is hit as below on database.

select employeebo0_.EMPID as EMPID0_, employeebo0_.DEPTID as DEPTID0_, employeebo0_.EMPADDRESS as EMPADDRESS0_, employeebo0_.EMPAGE as EMPAGE0_, employeebo0_.EMPNAME as EMPNAME0_, employeebo0_.SALARY as SALARY0_ from EMPLOYEE employeebo0_

但是我希望使用Eager访存来获取employee表和Department表的所有数据.

推荐答案

它按预期工作. EmployeeBO包含一个DepartmentBO.当您访问DepartmentBO时，它会自动填充.

It works as expected. The EmployeeBO contains a DepartmentBO. The DepartmentBO will automatically be filled the moment you access it.

如果包含EmployeeBO的Hibernate会话已结束，则情况并非如此.则EmployeeBO是瞬态的，休眠状态将不会获取丢失的对象.

This is not true, if the Hibernate session containing the EmployeeBO has ended. Then the EmployeeBO is transient and hibernate will not fetch the missing object.

要强制填写DepartmentBO，可以在hql代码中添加fetch子句.但这不再是懒惰获取.

To enforce filling the DepartmentBO, you can add a fetch clause to your hql code. But that is not lazy fetching any more.

HQL

from EmployeeBO join fetch EmployeeBO.department 

应执行此工作(将EmployeeBO替换为实际的实体名称).

should do the job (replace the EmployeeBO with the actual entity name).

请参阅此处的休眠文档: https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/queryhql.html ，对于此处的获取策略

See here in the hibernate docs: https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/queryhql.html and for the fetching strategies here https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/performance.html#performance-fetching

从注释中，您实际上希望热切获取关系，因此您需要声明fetchtype是热切的:

From the comments, you actually want eager fetching on the relationship, so you need to declare the fetchtype to be eager:

@ManyToOne(fetch=FetchType.EAGER)

应该修复它.在此处添加另一个文档: https://docs.oracle.com/javaee/6/api/javax/persistence/ManyToOne.html

should fix it. Adding another doc here: https://docs.oracle.com/javaee/6/api/javax/persistence/ManyToOne.html

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