Question

我正在尝试使用hibernate注释从数据库中获取数据，但它不能像我预期的那样工作。我有两个表Employee和Department。 java代码如下：

员工类

 @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 
    }

系类：

@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：

<?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>

当我尝试从员工和部门表中获取所有数据时，它只返回员工表中的数据，我的代码为hq查询，如下所示：

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

以上查询在数据库中命中如下。

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_

但我希望员工表和部门表的所有数据都使用Eager抓取。

Answer 1

它按预期工作。 EmployeeBO包含一个DepartmentBO。当您访问时，DepartmentBO将自动填充。

如果包含EmployeeBO的Hibernate会话已结束，则情况并非如此。然后EmployeeBO是瞬态的，而hibernate将不会获取丢失的对象。

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

HQL

from EmployeeBO join fetch EmployeeBO.department

应该完成这项工作（将EmployeeBO替换为实际的实体名称）。

请参阅hibernate docs：https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/queryhql.html以及此处的提取策略https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/performance.html#performance-fetching

从评论中，你实际上想要了解关系，所以你需要声明fetchtype是急切的：

@ManyToOne(fetch=FetchType.EAGER)

应该修复它。在此处添加其他文档：https://docs.oracle.com/javaee/6/api/javax/persistence/ManyToOne.html

Answer 2

有两种方法可以做到这一点： 1）使用EAGER获取类型 2）获得员工后，在每个员工上调用getDepartmentBO（）

Answer 3

我认为你错过了延迟加载的注释。

您必须在要延迟加载的关联上使用（fetch = FetchType.LAZY）

Answer 4

默认情况下，Hibernate具有延迟加载功能。即它不会获取另一个表的数据。在您的情况下，如果您想要部门表的数据，如果您在休眠会话中，则必须调用 departmentBO 的getter。注意：它将触发另一个查询。否则你也可以使用

Hibernate.initialize(entity.getdepartmentBO())

如果您希望默认获取部门数据。使用以下代码

@ManyToOne(fetch=FetchType.EAGER)

Hibernate多对一渴望获取不工作

4 个答案: