Hibernate的一对一映射

一、创建Java工程，新建Lib文件夹，加入Hibernate和数据库（如MySql、Oracle、SqlServer等）的Jar包，创建 hibernate.cfg.xml 文件，并配置，配置项如下：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-configuration PUBLIC
 3         "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 4         "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 5 <hibernate-configuration>
 6     <session-factory>
 7     
 8         <!-- 配置连接数据库的基本信息 -->
 9         <property name="connection.username">root</property>
10         <property name="connection.password"></property>
11         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
12         <!-- <property name="connection.url">jdbc:mysql:///mis</property> -->
13         <property name="connection.url">
14             <!-- 解决Mysql插入中文乱码的问题 -->
15             <![CDATA[jdbc:mysql://localhost:3306/mis?useUnicode=true&characterEncoding=utf8]]>
16         </property>
17 
18 
19         <!-- 配置 hibernate 的基本信息 -->
20         <!-- hibernate 所使用的数据库方言 -->
21         <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>
22 
23         <!-- 执行操作时是否在控制台打印 SQL -->
24         <property name="show_sql">true</property>
25 
26         <!-- 是否对 SQL 进行格式化 -->
27         <property name="format_sql">true</property>
28 
29         <!-- 指定自动生成数据表的策略 -->
30         <property name="hbm2ddl.auto">update</property>
31         
32         <!-- 设置 Hibernate 的事务隔离级别 2:读已提交的记录-->
33         <property name="connection.isolation">2</property>
34         
35         <!-- 删除对象后, 使其 OID 置为 null -->
36         <property name="use_identifier_rollback">true</property>
37         
38         <!-- 配置 C3P0 数据源 -->
39         <property name="hibernate.c3p0.max_size">10</property>
40         <property name="hibernate.c3p0.min_size">5</property>
41         <property name="c3p0.acquire_increment">2</property>
42         
43         <property name="c3p0.idle_test_period">2000</property>
44         <property name="c3p0.timeout">2000</property>
45         
46         <property name="c3p0.max_statements">10</property>
47         
48         <!-- 设定 JDBC 的 Statement 读取数据的时候每次从数据库中取出的记录条数 -->
49         <property name="hibernate.jdbc.fetch_size">100</property>
50         
51         <!-- 设定对数据库进行批量删除，批量更新和批量插入的时候的批次大小 -->
52         <property name="jdbc.batch_size">30</property>
53 
54         <!-- 指定关联的 .hbm.xml 文件 -->
55         <!-- 
56         <mapping resource="com/mcs/hibernate/entities/News.hbm.xml" />
57         <mapping resource="com/mcs/hibernate/entities/Worker.hbm.xml" />
58         
59         <mapping resource="com/mcs/hibernate/entities/n21/Customer.hbm.xml" />
60         <mapping resource="com/mcs/hibernate/entities/n21/Order.hbm.xml" />
61          -->
62          
63         <mapping resource="com/mcs/hibernate/entities/n21/both/Customer.hbm.xml" />
64         <mapping resource="com/mcs/hibernate/entities/n21/both/Order.hbm.xml" />
65 
66     </session-factory>
67 
68 </hibernate-configuration>

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二、基于外键的一对一映射

1、创建Java实体类

 1 package com.mcs.hibernate.entities.onetoone.foreign;
 2 
 3 public class Department {
 4     
 5     private Integer departmentId;
 6     private String departmentName;
 7     
 8     private Manager manager;
 9 
10     public Integer getDepartmentId() {
11         return departmentId;
12     }
13 
14     public void setDepartmentId(Integer departmentId) {
15         this.departmentId = departmentId;
16     }
17 
18     public String getDepartmentName() {
19         return departmentName;
20     }
21 
22     public void setDepartmentName(String departmentName) {
23         this.departmentName = departmentName;
24     }
25 
26     public Manager getManager() {
27         return manager;
28     }
29 
30     public void setManager(Manager manager) {
31         this.manager = manager;
32     }
33     
34     
35 
36 }

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 1 package com.mcs.hibernate.entities.onetoone.foreign;
 2 
 3 public class Manager {
 4     
 5     private Integer managerId;
 6     private String managerName;
 7     
 8     private Department department;
 9 
10     public Integer getManagerId() {
11         return managerId;
12     }
13 
14     public void setManagerId(Integer managerId) {
15         this.managerId = managerId;
16     }
17 
18     public String getManagerName() {
19         return managerName;
20     }
21 
22     public void setManagerName(String managerName) {
23         this.managerName = managerName;
24     }
25 
26     public Department getDepartment() {
27         return department;
28     }
29 
30     public void setDepartment(Department department) {
31         this.department = department;
32     }
33     
34     
35 
36 }

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2、根据实体类创建对应的 hbm.xml文件

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2015-10-28 13:38:17 by Hibernate Tools 3.5.0.Final -->
 5 <hibernate-mapping>
 6     <class name="com.mcs.hibernate.entities.onetoone.foreign.Department" table="DEPARTMENTS">
 7         <id name="departmentId" type="java.lang.Integer">
 8             <column name="DEPARTMENT_ID" />
 9             <generator class="native" />
10         </id>
11         <property name="departmentName" type="java.lang.String">
12             <column name="DEPARTMENT_NAME" />
13         </property>
14         
15         <!-- 使用 many-to-one 的方式来映射 1-1 关联关系 -->
16         <many-to-one name="manager" 
17             class="com.mcs.hibernate.entities.onetoone.foreign.Manager"
18             column="MANAGER_ID"
19             unique="true"></many-to-one>
20     </class>
21 </hibernate-mapping>

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 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2015-10-28 13:38:17 by Hibernate Tools 3.5.0.Final -->
 5 <hibernate-mapping>
 6     <class name="com.mcs.hibernate.entities.onetoone.foreign.Manager" table="MANAGERS">
 7         <id name="managerId" type="java.lang.Integer">
 8             <column name="MANAGER_ID" />
 9             <generator class="native" />
10         </id>
11         <property name="managerName" type="java.lang.String">
12             <column name="MANAGER_NAME" />
13         </property>
14         
15         <!-- 映射 1-1 的关联关系: 在对应的数据表中已经有外键了, 当前持久化类使用 one-to-one 进行映射 -->
16         <!-- 
17             没有外键的一端需要使用one-to-one元素，该元素使用 property-ref 属性指定使用被关联实体主键以外的字段作为关联字段
18          -->
19         <one-to-one name="department" 
20             class="com.mcs.hibernate.entities.onetoone.foreign.Department"
21             property-ref="manager">
22         </one-to-one>
23     </class>
24 </hibernate-mapping>

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注：

　　1、在有外键的一端需要使用many-to-one元素，该元素使用 unique="true" 属性来约束唯一值，并指定外键栏 column="MANAGER_ID"

　　2、没有外键的一端需要使用one-to-one元素，该元素使用 property-ref 属性指定使用被关联实体主键以外的字段作为关联字段

　　3、在保存操作中，建议先保存没有外键列的那个对象. 这样会减少 UPDATE 语句

　　4、默认情况下对关联属性使用懒加载，注意可能会出现懒加载异常的问题。

　　5、在查询没有外键的实体对象时, 使用的左外连接查询, 一并查询出其关联的对象，并已经进行初始化。

三、基于主键的一对一映射

1、创建Java实体类

 1 package com.mcs.hibernate.entities.onetoone.primary;
 2 
 3 public class Department {
 4     
 5     private Integer departmentId;
 6     private String departmentName;
 7     
 8     private Manager manager;
 9 
10     public Integer getDepartmentId() {
11         return departmentId;
12     }
13 
14     public void setDepartmentId(Integer departmentId) {
15         this.departmentId = departmentId;
16     }
17 
18     public String getDepartmentName() {
19         return departmentName;
20     }
21 
22     public void setDepartmentName(String departmentName) {
23         this.departmentName = departmentName;
24     }
25 
26     public Manager getManager() {
27         return manager;
28     }
29 
30     public void setManager(Manager manager) {
31         this.manager = manager;
32     }
33     
34     
35 
36 }

View Code

 1 package com.mcs.hibernate.entities.onetoone.primary;
 2 
 3 public class Manager {
 4     
 5     private Integer managerId;
 6     private String managerName;
 7     
 8     private Department department;
 9 
10     public Integer getManagerId() {
11         return managerId;
12     }
13 
14     public void setManagerId(Integer managerId) {
15         this.managerId = managerId;
16     }
17 
18     public String getManagerName() {
19         return managerName;
20     }
21 
22     public void setManagerName(String managerName) {
23         this.managerName = managerName;
24     }
25 
26     public Department getDepartment() {
27         return department;
28     }
29 
30     public void setDepartment(Department department) {
31         this.department = department;
32     }
33     
34     
35 
36 }

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2、根据实体类创建对应的 hbm.xml文件

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2015-10-28 13:38:17 by Hibernate Tools 3.5.0.Final -->
 5 <hibernate-mapping>
 6     <class name="com.mcs.hibernate.entities.onetoone.primary.Department" table="DEPARTMENTS">
 7         <id name="departmentId" type="java.lang.Integer">
 8             <column name="DEPARTMENT_ID" />
 9             <!-- 使用外键的方式来生成当前的主键 -->
10             <generator class="foreign" >
11                 <!-- property 属性指定使用当前持久化类的哪一个属性的主键作为外键 -->
12                 <param name="property">manager</param>
13             </generator>
14         </id>
15         <property name="departmentName" type="java.lang.String">
16             <column name="DEPARTMENT_NAME" />
17         </property>
18         
19         <!--  
20         采用 foreign 主键生成器策略的一端增加 one-to-one 元素映射关联属性,
21         其 one-to-one 节点还应增加 constrained=true 属性, 以使当前的主键上添加外键约束
22         -->
23         <one-to-one name="manager" 
24             class="com.mcs.hibernate.entities.onetoone.primary.Manager"
25             constrained="true">
26         </one-to-one>
27     </class>
28 </hibernate-mapping>

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 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2015-10-28 13:38:17 by Hibernate Tools 3.5.0.Final -->
 5 <hibernate-mapping>
 6     <class name="com.mcs.hibernate.entities.onetoone.primary.Manager" table="MANAGERS">
 7         <id name="managerId" type="java.lang.Integer">
 8             <column name="MANAGER_ID" />
 9             <generator class="native" />
10         </id>
11         <property name="managerName" type="java.lang.String">
12             <column name="MANAGER_NAME" />
13         </property>
14 
15         <one-to-one name="department" 
16             class="com.mcs.hibernate.entities.onetoone.primary.Department">
17         </one-to-one>
18     </class>
19 </hibernate-mapping>

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注：

　　1、其中一端会使用另外一端的主键做为主键，另外一端代码采用 foreign 主键生成器策略的一端增加 one-to-one 元素映射关联属性,其 one-to-one 节点还应增加 constrained=true 属性, 以使当前的主键上添加外键约束。　

　　2、在保存操作中，建议先保存没有外键列的那个对象. 这样会减少 UPDATE 语句

　　3、默认情况下对关联属性使用懒加载，注意可能会出现懒加载异常的问题。

posted @ 2015-10-29 11:13 小个子猫阅读(314) 评论(0) 编辑收藏举报

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