[英]Hibernate many to one eager fetching not working
我正在嘗試使用休眠注釋從數據庫中獲取數據,但是它沒有按我的預期工作。 我有兩個表Employee和Department。 Java代碼如下:
員工階層
@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
}
部門類別:
@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>
當我嘗試從employee和department表中獲取所有數據,但它僅從employee表中返回數據時,我的命中hql查詢的代碼如下:
List<EmployeeBO> empList = null;
empList = sessionFactory.getCurrentSession().createQuery("From "+employeeBO.getClass().getName()).list();
上面的查詢在數據庫上命中如下。
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_
但是我想使用Eager訪存來獲取雇員表和部門表的所有數據。
它按預期工作。 EmployeeBO包含一個DepartmentBO。 當您訪問DepartmentBO時,它會自動填充。
如果包含EmployeeBO的休眠會話已結束,則情況並非如此。 然后,EmployeeBO是瞬態的,休眠狀態將不會獲取丟失的對象。
要強制填充DepartmentBO,可以在hql代碼中添加fetch
子句。 但這不再是懶惰獲取。
總部
from EmployeeBO join fetch EmployeeBO.department
應該做的工作(用實際的實體名稱替換EmployeeBO)。
請參閱hibernate文檔中的此處: https : //docs.jboss.org/hibernate/orm/3.3/reference/en/html/queryhql.html以及此處的獲取策略https://docs.jboss.org/hibernate/ orm / 3.3 / reference / zh-CN / html / performance.html#performance-fetching
從注釋中,您實際上想渴望獲取關系,因此您需要聲明fetchtype渴望:
@ManyToOne(fetch=FetchType.EAGER)
應該修復它。 在此處添加另一個文檔: https : //docs.oracle.com/javaee/6/api/javax/persistence/ManyToOne.html
有兩種方法可以執行此操作:1)使用EAGER訪存類型2)在獲得雇員后,在每個雇員上調用getDepartmentBO()
我認為您已經錯過了延遲加載的注釋。
您必須在要延遲加載的關聯上使用(fetch = FetchType.LAZY)
休眠默認情況下具有延遲加載。 即它不會獲取另一個表的數據。 在這種情況下,如果要獲取部門表的數據,則在休眠會話中必須調用部門 BO的getter。 注意:它將觸發另一個查詢。 否則你也可以使用
Hibernate.initialize(entity.getdepartmentBO())
默認情況下是否要獲取部門數據。 使用以下代碼
@ManyToOne(fetch=FetchType.EAGER)
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