Hibernate学习笔记之关联关系

这个星期在看《Hibernate开发指南》，边看边动手做了小例子，先记录下来。

Hibernate的关联关系映射主要有三种：
一对一关联
一对多关联
多对多关联

 

一、使用*.hbm.xml配置文件做简单示例

一对一关联包括两种形式：主键关联、唯一外键关联
主键关联：两张关联表通过主键形成一对一的映射关系。Hibernate中通过one-to-one节点对一对一关系进行定义。
示例：一个用户User属于一个组Group
User实体类：

public class User {private Integer id;private String name;private Group group;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Group getGroup() {return group;}public void setGroup(Group group) {this.group = group;}}

Group实体类：

public class Group {private Integer id;private String name;private User user;public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public User getUser() {return user;}public void setUser(User user) {this.user = user;}}

User.hbm.xml

<hibernate-mapping> <class name="com.petrochina.User" table="cui_user" dynamic-update="true" dynamic-insert="true"> <id name="id" type="java.lang.Integer"> <generator class="native" /> </id> <property name="name" type="java.lang.String"/> <one-to-one name="group" class="com.petrochina.Group" cascade="all" outer-join="auto"></one-to-one> </class></hibernate-mapping>

Group.hbm.xml

<hibernate-mapping> <class name="com.petrochina.Group" table="cui_group" > <id name="id" type="java.lang.Integer"> <generator class="foreign" >//foreign主键生成 <param name="property">user</param> </generator> </id> <property name="name" type="java.lang.String"/> <one-to-one name="user" class="com.petrochina.User"></one-to-one> </class></hibernate-mapping>

测试方法：

public void oneToOne() {try {User user=new User();user.setName("two");Group group=new Group();group.setName("测试");group.setUser(user);user.setGroup(group);Transaction tx=session.beginTransaction();session.save(user);tx.commit();System.out.println(user.getName());} catch (Exception e) {e.printStackTrace();}}

 

唯一外键关联：通过增加外键字段实现，这种方式是多对一关系的一个特例。
User类没有变化，Group类中去掉user字段：

public class Group {private Integer id;private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}}

User.hbm.xml

<hibernate-mapping> <class name="com.petrochina.User" table="one_user" dynamic-update="true" dynamic-insert="true"> <id name="id" type="java.lang.Integer"> <generator class="native" /> </id> <property name="name" type="java.lang.String"/> <many-to-one name="group" column="group_id" class="com.petrochina.Group" cascade="all" />//定义group_id字段 </class></hibernate-mapping>

Group.hbm.xml

<hibernate-mapping> <class name="com.petrochina.Group" table="cui_group" > <id name="id" type="java.lang.Integer"> <generator class="assigned" > </generator> </id> <property name="name" type="java.lang.String"/> </class></hibernate-mapping>

测试方法：

public void oneToOne() {try {Transaction tx=session.beginTransaction();User user=new User();user.setName("three");Group group=new Group();group.setId(999);group.setName("测试3");user.setGroup(group);session.save(user);tx.commit();System.out.println(user.getName());} catch (Exception e) {e.printStackTrace();}}

注意：hibernate.cfg.xml的映射文件中不能存在同名文件，即使路径不一样。

 

二、使用JPA实现*.hbm.xml相同的功能
首先，使用JPA需要更改HibernateSessionFactory中Configuration的实现：private  static Configuration configuration = new

AnnotationConfiguration(); 或者在自定义Configuration cfg=new AnnotationConfiguration().configure();
其次，去掉hibernate.cfg.xml中<mapping resource="com/petrochina/onetoone/User.hbm.xml" />部分对映射文件的配置，改为<mapping class="com.petrochina.jpa.User" />
1、一对一

一对一关系有三种情况

示例：用户User、组Group

(1)关联的实体都共享同样的主键

1)一对一双向关联

@Entity@Table(name="t_user")public class User {private Integer id;private String name;private Group group;@Id@GeneratedValue(strategy=GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToOne(cascade=CascadeType.ALL)@PrimaryKeyJoinColumnpublic Group getGroup() {return group;}public void setGroup(Group group) {this.group = group;}}@Entity@Table(name="t_group")public class Group {private Integer id;private String name;private User user;@Id@GenericGenerator(name="pkGenerator",strategy="foreign",parameters={@Parameter(value="user", name = "property")})@GeneratedValue(generator="pkGenerator")//根据User的id填充Group的idpublic Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToOne(cascade=CascadeType.ALL,mappedBy="group")public User getUser() {return user;}public void setUser(User user) {this.user = user;}}

执行插入测试方法：

public void oneToOne() {try {Transaction tx=session.beginTransaction();User user=new User();user.setName("csdner");Group group=new Group();group.setName("developer");user.setGroup(group);group.setUser(user);session.save(user);tx.commit();} catch (Exception e) {e.printStackTrace();}}

Hibernate生成的sql语句如下：

Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into t_user (name, id) values (?, ?)
Hibernate: insert into t_group (name, id) values (?, ?)

查询表里的数据

SQL> select * from t_user;
        ID      NAME                                                                           
--------------------------------------------------------------------------------
       276      csdner                                                                                                                                              

SQL> select * from t_group;
        ID      NAME                                                                           
--------------------------------------------------------------------------------
       276      developer                                                             

可见，User和Group有相同的ID。

执行查询测试方法：

public void getUser() {User user=(User)session.load(User.class, 276);System.out.println(user.getName());System.out.println(user.getGroup().getName());}

Hibernate生成的sql语句如下：

select user0_.id    as id2_2_,
       user0_.name  as name2_2_,
       group1_.id   as id3_0_,
       group1_.name as name3_0_,
       user2_.id    as id2_1_,
       user2_.name  as name2_1_
  from t_user user0_
  left outer join t_group group1_
    on user0_.id = group1_.id
  left outer join t_user user2_
    on group1_.id = user2_.id
 where user0_.id = ?
 csdner

 developer

可见User和Group通过ID关联。

 

2）一对一单向关联

@Entity@Table(name="t_user")public class User {private Integer id;private String name;@Id@GeneratedValue(strategy=GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}}@Entity@Table(name="t_group")public class Group {private Integer id;private String name;private User user;@Id@GenericGenerator(name="pkGenerator",strategy="foreign",parameters={@Parameter(value="user", name = "property")})@GeneratedValue(generator="pkGenerator")public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToOne(cascade=CascadeType.ALL)@PrimaryKeyJoinColumnpublic User getUser() {return user;}public void setUser(User user) {this.user = user;}}

执行插入测试方法：

public void oneToOne() {try {Transaction tx=session.beginTransaction();User user=new User();user.setName("csdner");Group group=new Group();group.setName("developer");group.setUser(user);session.save(group);//保存group，同时级联保存usertx.commit();} catch (Exception e) {e.printStackTrace();}}

Hibernate生成的sql语句如下：

Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into t_user (name, id) values (?, ?)
Hibernate: insert into t_group (name, id) values (?, ?)

查询表里的数据：

SQL> select * from t_user;

        ID NAME
---------- --------------------
       280 csdner

SQL> select * from t_group;

        ID NAME
---------- --------------------
       280 developer

User对象和Group对象也有相同的ID，但是由于是单向的，只能通过Group对象查找对应的User对象。

 

(2)其中一个实体通过外键关联到另一个实体的主键。注：一对一，则外键必须为唯一约束

 @Entity@Table(name="t_user")public class User {private Integer id;private String name;private Group group;@Id@GeneratedValue(strategy=GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToOne(cascade=CascadeType.ALL)@JoinColumn(name="gp_id")//定义关联列的列名，默认为“group_id”public Group getGroup() {return group;}public void setGroup(Group group) {this.group = group;}}@Entity@Table(name="t_group")public class Group {private Integer id;private String name;private User user;@Id@GeneratedValue//@GenericGenerator(name="pkGenerator",strategy="foreign",parameters={@Parameter(value="user", name = "property")})//@GeneratedValue(generator="pkGenerator")public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToOne(cascade=CascadeType.ALL,mappedBy="group")public User getUser() {return user;}public void setUser(User user) {this.user = user;}}

通过@JoinColumn注解定义一对一的关联关系。如果没有@JoinColumn注解，则系统自动处理，在主表中将创建连接列，列名为：主题的关联属性名 + 下划线 + 被关联端的主键列名。

执行插入测试代码：

public void oneToOne() {try {Transaction tx=session.beginTransaction();User user=new User();user.setName("csdner");Group group=new Group();group.setName("developer");user.setGroup(group);group.setUser(user);session.save(user);tx.commit();} catch (Exception e) {e.printStackTrace();}}

Hibernate生成的sql语句如下：

Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into t_group (name, id) values (?, ?)
Hibernate: insert into t_user (gp_id, name, id) values (?, ?, ?)

查询表里的数据：

SQL> select * from t_user;

        ID NAME                      GP_ID
---------- -------------------- ----------
       287 csdner                      288

SQL> select * from t_group;

        ID NAME
---------- --------------------
       288 developer

User对象通过group_id 列关联Group对象

 

(3)通过关联表来保存两个实体之间的关联关系。注：一对一，则关联表每个外键都必须是唯一约束

@Entity@Table(name="t_user")public class User {private Integer id;private String name;private Group group;@Id@GeneratedValue(strategy=GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToOne(cascade=CascadeType.ALL)@JoinTable(name="t_user_group",joinColumns={@JoinColumn(name="user_id",referencedColumnName="id")},inverseJoinColumns={@JoinColumn(name="group_id",referencedColumnName="id")})//指定关联表t_user_group,其中与User关联的列为user_id，与Group关联的列为group_idpublic Group getGroup() {return group;}public void setGroup(Group group) {this.group = group;}}@Entity@Table(name="t_group")public class Group {private Integer id;private String name;//private User user;//不能含有user，否则会报错，后续再看看@Id@GeneratedValuepublic Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}//@OneToOne(mappedBy="group")//public User getUser() {//return user;//}//public void setUser(User user) {//this.user = user;//}}

执行插入测试方法：

public void oneToOne() {try {Transaction tx=session.beginTransaction();User user=new User();user.setName("csdner");Group group=new Group();group.setName("developer");user.setGroup(group);session.save(user);tx.commit();} catch (Exception e) {e.printStackTrace();}}

Hibernate生成的sql语句如下：

Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into t_group (name, id) values (?, ?)
Hibernate: insert into t_user (name, id) values (?, ?)
Hibernate: insert into t_user_group (group_id, user_id) values (?, ?)

查询表里的数据：

 SQL> select * from t_user;

        ID NAME
---------- --------------------
       313 csdner

SQL> select * from t_group;

        ID NAME
---------- --------------------
       314 developer

SQL> select * from t_user_group;

   USER_ID   GROUP_ID
---------- ----------
       313        314

 

2、一对多

一对多关联包括两种形式：单向一对多关联、双向一对多关联
单向一对多关联只需在“一”方进行配置（onetomany），即通过“一”关联到“多”。双向一对多需要关联双方均加以配置，这样既能通过“一”关联其对应的“多”，也可以通过“多”关联其对应的“一”。以用户TUser和地址TAddress做演示

单向一对多：只在TUser类中维护@OneToMany

//用户类TUser.java@Entity@Table(name="cui_user")public class TUser {private Integer id;private String name;private List<TAddress> addresses=new ArrayList<TAddress>();//注意一定要实例化@Id//标识主键@GeneratedValue(strategy=GenerationType.AUTO)//指定主键值的产生策略由Hibernate根据数据库字段选择public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToMany(fetch=FetchType.LAZY,cascade=CascadeType.ALL)//FetchType.LAZY延迟加载，CascadeType.ALL所有操作都同步@JoinColumn(name="user_id",referencedColumnName="id")//在TAddress对应的表中增加关联列user_id,其值对应TUser的id字段@OrderBy(value="id asc")//所去地址列表按id升序排列public List<TAddress> getAddresses() {return addresses;}public void setAddresses(List<TAddress> addresses) {this.addresses = addresses;}}//地址类TAddress.java@Entity@Table(name="cui_addr")public class TAddress {private Integer id;private String zipCode;private String addr;@Id@GeneratedValue(strategy=GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}@Column(name="zip_code")public String getZipCode() {return zipCode;}public void setZipCode(String zipCode) {this.zipCode = zipCode;}public String getAddr() {return addr;}public void setAddr(String addr) {this.addr = addr;}}

测试方法：

public void oneToMany() {try {Transaction tx=session.beginTransaction();TUser user=new TUser();user.setName("test");TAddress addr1=new TAddress();addr1.setZipCode("027");addr1.setAddr("武汉");TAddress addr2=new TAddress();addr2.setZipCode("021");addr2.setAddr("上海");user.getAddresses().add(addr1);user.getAddresses().add(addr2);session.save(user);tx.commit();} catch (Exception e) {e.printStackTrace();}}

对应的Hibernate生成的sql语句如下：
Hibernate: insert into cui_user (name, id) values (?, ?)
Hibernate: insert into cui_addr (addr, zip_code, id) values (?, ?, ?)
Hibernate: insert into cui_addr (addr, zip_code, id) values (?, ?, ?)
Hibernate: update cui_addr set user_id=? where id=?
Hibernate: update cui_addr set user_id=? where id=?
可见单向一对多中Hibernate是先插入TAddress记录，然后再维护关联关系字段user_id.

 

双向一对多：在TUser类中维护@OneToMany，在TAddress类中维护@ManyToOne

 //用户类TUser.java@Entity@Table(name="cui_user")public class TUser {private Integer id;private String name;private List<TAddress> addresses=new ArrayList<TAddress>();//注意一定要实例化@Id//标识主键@GeneratedValue(strategy=GenerationType.AUTO)//指定主键值的产生策略由Hibernate根据数据库字段选择public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}//fetch=FetchType.LAZY延迟加载，cascade=CascadeType.ALL所有操作都同步@OneToMany(fetch=FetchType.LAZY,cascade=CascadeType.ALL,mappedBy="user")@OrderBy(value="id asc")//所去地址列表按id升序排列public List<TAddress> getAddresses() {return addresses;}public void setAddresses(List<TAddress> addresses) {this.addresses = addresses;}}//地址类TAddress.java@Entity@Table(name="cui_addr")public class TAddress {private Integer id;private String zipCode;private String addr;private TUser user;@Id@GeneratedValue(strategy=GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}@Column(name="zip_code")public String getZipCode() {return zipCode;}public void setZipCode(String zipCode) {this.zipCode = zipCode;}public String getAddr() {return addr;}public void setAddr(String addr) {this.addr = addr;}@ManyToOne@JoinColumn(name="user_id",referencedColumnName="id")//在TAddress对应的表中增加关联列user_id,其值对应TUser的id字段public TUser getUser() {return user;}public void setUser(TUser user) {this.user = user;}}

测试代码：

public void oneToMany() {try {Transaction tx=session.beginTransaction();TUser user=new TUser();user.setName("test");TAddress addr1=new TAddress();addr1.setZipCode("027");addr1.setAddr("武汉");TAddress addr2=new TAddress();addr2.setZipCode("021");addr2.setAddr("上海");addr1.setUser(user);addr2.setUser(user);user.getAddresses().add(addr1);user.getAddresses().add(addr2);session.save(user);tx.commit();System.out.println(user.getName());} catch (Exception e) {e.printStackTrace();}}

对应的Hibernate生成的sql语句如下：
Hibernate: insert into cui_user (name, id) values (?, ?)
Hibernate: insert into cui_addr (addr, user_id, zip_code, id) values (?, ?, ?, ?)
Hibernate: insert into cui_addr (addr, user_id, zip_code, id) values (?, ?, ?, ?)
可见在双向一对多关联中在新增TAddress记录时直接将关联字段user_id填充了，相比单向一对多少了两条更新语句。

 

3、多对多

示例：角色Role、权限Privilege

 @Entity@Table(name="t_role")public class Role {private Integer id;private String name;private Set<Privilege> privileges=new HashSet<Privilege>();@Id@GeneratedValue(strategy=GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@ManyToMany(fetch=FetchType.LAZY)@JoinTable(name="t_role_privilege",joinColumns={@JoinColumn(name="role_id",referencedColumnName="id")},inverseJoinColumns={@JoinColumn(name="privilege_id",referencedColumnName="id")})public Set<Privilege> getPrivileges() {return privileges;}public void setPrivileges(Set<Privilege> privileges) {this.privileges = privileges;}}@Entity@Table(name="t_privilege")public class Privilege {private Integer id;private String name;private Set<Role> roles=new HashSet<Role>();@Id@GeneratedValue(strategy=GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@ManyToMany(mappedBy="privileges")public Set<Role> getRoles() {return roles;}public void setRoles(Set<Role> roles) {this.roles = roles;}}

测试方法：

public void manyToMany() {Role role1=new Role();role1.setName("Role1");Role role2=new Role();role2.setName("Role2");Privilege privilege1=new Privilege();privilege1.setName("Privilege1");Privilege privilege2=new Privilege();privilege2.setName("Privilege2");privilege1.getRoles().add(role1);privilege1.getRoles().add(role2);privilege2.getRoles().add(role1);role1.getPrivileges().add(privilege1);role1.getPrivileges().add(privilege2);role2.getPrivileges().add(privilege1);Transaction tx=session.beginTransaction();//多对多关系必须同时对关联双方进行保存session.save(privilege1);session.save(privilege2);session.save(role1);session.save(role2);tx.commit();}

对应的Hibernate生成的sql语句如下：
Hibernate: insert into t_privilege (name, id) values (?, ?)
Hibernate: insert into t_privilege (name, id) values (?, ?)
Hibernate: insert into t_role (name, id) values (?, ?)
Hibernate: insert into t_role (name, id) values (?, ?)
Hibernate: insert into t_role_privilege (role_id, privilege_id) values (?, ?)
Hibernate: insert into t_role_privilege (role_id, privilege_id) values (?, ?)
Hibernate: insert into t_role_privilege (role_id, privilege_id) values (?, ?)