Hibernate继承注解
hibernate应用中，继承的用途或目的主要有两点：
- 组件化：故明思义，把重复性的代码抽取成组件，以便重用和维护。hibernate应用中，一些重复的字段，重复的映射配置，就需要抽取成组件。
- 多态性：类的多态性是指下层业务所需一个父类对象，而上层业务根据所需的父类对象，传递一个子类对象。hibernate应用中，下层业务操作父类对象进行持久操作，如增删改查，上层业务则传递一个子类对象。
所以，在应用hibernate的继承时，需要明确设计所需，即究竟是组件化需求，还是多态性需求。
- @MappedSuperclass：组件化需求的继承注解。虽然它可以应用于类的多态性业务中，但它不能应用于hibernate持久操作的多态性业务中。
- @Inheritance：多态性需求的继承注解。虽然它可以达到组件化的目的，但它要比@MappedSuperclass多负出一些代价。
@MappedSuperclass定义：
@Documented
@Target({TYPE})
@Retention(RUNTIME)
public @interface MappedSuperclass {
}
@Inheritance定义：
@Target({TYPE})
@Retention(RUNTIME)
public @interface Inheritance {
InheritanceType strategy() default SINGLE_TABLE;
}
InheritanceType定义：
public enum InheritanceType {
SINGLE_TABLE,
TABLE_PER_CLASS,
JOINED
}
从定义看出，@Inheritance的默认继承策略为SINGLE_TABLE，三种继承策略的区别在于：
- SINGLE_TABLE：公共属性公共表，独立属性公共表。
需要使用监别器区分具体的子类，注解@DiscriminatorColumn设置监别器列，注解@DiscriminatorValue设置监别器值。
子类的属性映射配置时，需要设置为允许为空或默认值。 - JOINED：公共属性公共表，独立属性独立表。
子类的独立表生成后，其主键是一个共享主键，意味着这是一对一的关联，默认名称与父类的主键一致，使用注解@PrimaryKeyJoinColumn可改变名称。 - TABLE_PER_CLASS：公共属性独立表，独立属性独立表。
主键生成策略不能使用GenerationType.IDENTITY。
对于子类而言，公共属性就是父类的属性，公共表就是父类对应的表，而独立属性就是自己定义的属性，独立表就是自己对应的表。
示例1：继承注解@MappedSuperclass
User.java
@MappedSuperclass
public class User<ID extends Serializable> {
//---------------------------------------------------------------
// Field
//--------------------------------------------------------------- @Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private ID id; @Column(name = "loginName",
length = 20,
unique = true,
nullable = false,
updatable = false)
private String loginName; @Column(name = "loginPass",
length = 20,
nullable = false)
private String loginPass; //---------------------------------------------------------------
// Method
//--------------------------------------------------------------- public ID getId() {
return id;
} public void setId(ID id) {
this.id = id;
} public String getLoginName() {
return loginName;
} public void setLoginName(String loginName) {
this.loginName = loginName;
} public String getLoginPass() {
return loginPass;
} public void setLoginPass(String loginPass) {
this.loginPass = loginPass;
}
}
Admin.java
@Entity
@Table
public class Admin extends User<Integer> {
@Column(name = "role", length = 20, nullable = false)
private String role; public String getRole() {
return role;
} public void setRole(String role) {
this.role = role;
}
}
Member.java
@Entity
@Table
public class Member extends User<Long> {
@Column(name = "name", length = 20, nullable = false)
private String name; public String getName() {
return name;
} public void setName(String name) {
this.name = name;
}
}
test.java
public class Test {
public static void main(String[] params){
// 继承注解：@MappedSuperclass
new Test().test();
/*
Hibernate:
drop table if exists Admin
Hibernate:
drop table if exists Member
Hibernate:
create table Admin (
id integer not null auto_increment,
loginName varchar(20) not null,
loginPass varchar(20) not null,
role varchar(20) not null,
primary key (id)
)
Hibernate:
create table Member (
id bigint not null auto_increment,
loginName varchar(20) not null,
loginPass varchar(20) not null,
name varchar(20) not null,
primary key (id)
)
Hibernate:
alter table Admin
add constraint UK_bdsh7mq6s6xad6ohm08u18uxr unique (loginName)
Hibernate:
alter table Member
add constraint UK_jxtse8o1c6l89j39lilw5e2rs unique (loginName)
Hibernate:
insert
into
Admin
(loginName, loginPass, role)
values
(?, ?, ?)
Hibernate:
select
last_insert_id()
Hibernate:
drop table if exists Admin
Hibernate:
drop table if exists Member
*/
}
public void test(){
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml", this.getClass());
SessionFactory factory = null;
boolean success = true;
Session session = null;
try {
factory = (SessionFactory) context.getBean("sessionFactory");
session = factory.openSession();
success = false;
session.beginTransaction();
User<?> user = new Admin();
user.setLoginName("loginName");
user.setLoginPass("loginPass");
((Admin)user).setRole("role");
session.save(user);
session.getTransaction().commit();
success = true;
} finally {
if(session != null){
if(!success)
session.getTransaction().rollback();
session.close();
session = null;
}
if(factory != null){
factory.close();
factory = null;
}
}
}
}
示例2：继承注解@Inheritance，继承策略InheritanceType.SINGLE_TABLE。
User.java
@Entity
@Table
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(
name = "type",
discriminatorType = DiscriminatorType.STRING,
length = 30)
@DiscriminatorValue("User")
public class User {
//---------------------------------------------------------------
// Field
//--------------------------------------------------------------- @Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id; @Column(name = "loginName",
length = 20,
unique = true,
nullable = false,
updatable = false)
private String loginName; @Column(name = "loginPass",
length = 20,
nullable = false)
private String loginPass; //---------------------------------------------------------------
// Method
//--------------------------------------------------------------- public Long getId() {
return id;
} public void setId(Long id) {
this.id = id;
} public String getLoginName() {
return loginName;
} public void setLoginName(String loginName) {
this.loginName = loginName;
} public String getLoginPass() {
return loginPass;
} public void setLoginPass(String loginPass) {
this.loginPass = loginPass;
}
}
Admin.java
@Entity
@DiscriminatorValue("Admin")
public class Admin extends User {
// 需要允许为空或设置默认值
@Column(name = "role", length = 20, nullable = true)
private String role; public String getRole() {
return role;
} public void setRole(String role) {
this.role = role;
}
}
Member.java
@Entity
@DiscriminatorValue("Member")
public class Member extends User {
// 需要允许为空或设置默认值
@Column(name = "name", length = 20, nullable = false, columnDefinition="VARCHAR(20) DEFAULT 'admin'")
private String name; public String getName() {
return name;
} public void setName(String name) {
this.name = name;
}
}
Test.java
public class Test {
public static void main(String[] params){
// 继承注解：@Inheritance
// 继承策略：InheritanceType.SINGLE_TABLE
// 公共属性公共表，独立属性公共表
new Test().test();
/*
Hibernate:
drop table if exists User
Hibernate:
create table User (
type varchar(30) not null,
id bigint not null auto_increment,
loginName varchar(20) not null,
loginPass varchar(20) not null,
role VARCHAR(20) DEFAULT 'member' not null,
name VARCHAR(20) DEFAULT 'admin' not null,
primary key (id)
)
Hibernate:
alter table User
add constraint UK_5iebj9qwxsnoshbaq6w834t0y unique (loginName)
Hibernate:
insert
into
User
(loginName, loginPass, role, type)
values
(?, ?, ?, 'Admin')
Hibernate:
select
last_insert_id()
Hibernate:
select
user0_.id as id2_0_0_,
user0_.loginName as loginNam3_0_0_,
user0_.loginPass as loginPas4_0_0_,
user0_.role as role5_0_0_,
user0_.name as name6_0_0_,
user0_.type as type1_0_0_
from
User user0_
where
user0_.id=?
多态性读取成功：study.t2.Admin@dc3aae
Hibernate:
drop table if exists User
*/
}
public void test(){
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml", this.getClass());
SessionFactory factory = null;
try {
factory = (SessionFactory) context.getBean("sessionFactory");
// 多态性添加
boolean success = true;
Session session = null;
Long id = null;
try {
session = factory.openSession();
success = false;
session.beginTransaction();
User user = new Admin();
user.setLoginName("loginName");
user.setLoginPass("loginPass");
((Admin)user).setRole("role");
session.save(user);
session.getTransaction().commit();
id = user.getId();
success = true;
} finally {
if(session != null){
if(!success)
session.getTransaction().rollback();
session.close();
session = null;
}
}
// 多态性读取
if(success){
try {
session = factory.openSession();
session.beginTransaction();
success = false;
User user = session.load(User.class, id);
System.out.println("多态性读取成功：" + user);
session.getTransaction().commit();
success = true;
} finally {
if(session != null){
if(!success)
session.getTransaction().rollback();
session.close();
session = null;
}
}
}
} finally {
if(factory != null){
factory.close();
factory = null;
}
}
}
}
示例3：继承注解@Inheritance，继承策略InheritanceType.JOINED。
User.java
@Entity
@Table
@Inheritance(strategy = InheritanceType.JOINED)
public class User { //---------------------------------------------------------------
// Field
//---------------------------------------------------------------
@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id; @Column(name = "loginName",
length = 20,
unique = true,
nullable = false,
updatable = false)
private String loginName; @Column(name = "loginPass",
length = 20,
nullable = false)
private String loginPass; //---------------------------------------------------------------
// Method
//--------------------------------------------------------------- public Long getId() {
return id;
} public void setId(Long id) {
this.id = id;
} public String getLoginName() {
return loginName;
} public void setLoginName(String loginName) {
this.loginName = loginName;
} public String getLoginPass() {
return loginPass;
} public void setLoginPass(String loginPass) {
this.loginPass = loginPass;
}
}
Admin.java
@Entity
@Table
// 可选，设置共享主键的名称，默认的主键名称与父类一致。
@PrimaryKeyJoinColumn(name = "userId")
public class Admin extends User {
@Column(name = "role", length = 20, nullable = false)
private String role; public String getRole() {
return role;
} public void setRole(String role) {
this.role = role;
}
}
Member.java
@Entity
@Table
// 可选，设置共享主键的名称，默认的主键名称与父类一致。
@PrimaryKeyJoinColumn(name = "userId")
public class Member extends User {
@Column(name = "name", length = 20, nullable = false)
private String name; public String getName() {
return name;
} public void setName(String name) {
this.name = name;
}
}
Test.java
public class Test {
public static void main(String[] params){
// 继承注解：@Inheritance
// 继承策略：InheritanceType.JOINED
// 公共属性公共表，独立属性独立表
new Test().test();
/*
Hibernate:
alter table Admin
drop
foreign key FKjoav33p64suikub3369fpajy4
注：这里可能报一个异常，因为表Admin不存在！
Hibernate:
alter table Member
drop
foreign key FKnj6wlxlj0cc3993su1qaykn42
注：这里可能报一个异常，因为表Member不存在！
Hibernate:
drop table if exists Admin
Hibernate:
drop table if exists Member
Hibernate:
drop table if exists User
Hibernate:
create table Admin (
role varchar(20) not null,
userId bigint not null,
primary key (userId)
)
Hibernate:
create table Member (
name varchar(20) not null,
userId bigint not null,
primary key (userId)
)
Hibernate:
create table User (
id bigint not null auto_increment,
loginName varchar(20) not null,
loginPass varchar(20) not null,
primary key (id)
)
Hibernate:
alter table User
add constraint UK_5iebj9qwxsnoshbaq6w834t0y unique (loginName)
Hibernate:
alter table Admin
add constraint FKjoav33p64suikub3369fpajy4
foreign key (userId)
references User (id)
Hibernate:
alter table Member
add constraint FKnj6wlxlj0cc3993su1qaykn42
foreign key (userId)
references User (id)
Hibernate:
insert
into
User
(loginName, loginPass)
values
(?, ?)
Hibernate:
select
last_insert_id()
Hibernate:
insert
into
Admin
(role, userId)
values
(?, ?)
Hibernate:
select
user0_.id as id1_2_0_,
user0_.loginName as loginNam2_2_0_,
user0_.loginPass as loginPas3_2_0_,
user0_1_.role as role1_0_0_,
user0_2_.name as name1_1_0_,
case
when user0_1_.userId is not null then 1
when user0_2_.userId is not null then 2
when user0_.id is not null then 0
end as clazz_0_
from
User user0_
left outer join
Admin user0_1_
on user0_.id=user0_1_.userId
left outer join
Member user0_2_
on user0_.id=user0_2_.userId
where
user0_.id=?
多态性读取成功：study.t3.Admin@1f9407e
Hibernate:
alter table Admin
drop
foreign key FKjoav33p64suikub3369fpajy4
Hibernate:
alter table Member
drop
foreign key FKnj6wlxlj0cc3993su1qaykn42
Hibernate:
drop table if exists Admin
Hibernate:
drop table if exists Member
Hibernate:
drop table if exists User
*/
}
public void test(){
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml", this.getClass());
SessionFactory factory = null;
try {
factory = (SessionFactory) context.getBean("sessionFactory");
// 多态性添加
boolean success = true;
Session session = null;
Long id = null;
try {
session = factory.openSession();
success = false;
session.beginTransaction();
User user = new Admin();
user.setLoginName("loginName");
user.setLoginPass("loginPass");
((Admin)user).setRole("role");
session.save(user);
session.getTransaction().commit();
id = user.getId();
success = true;
} finally {
if(session != null){
if(!success)
session.getTransaction().rollback();
session.close();
session = null;
}
}
// 多态性读取
if(success){
try {
session = factory.openSession();
session.beginTransaction();
success = false;
User user = session.load(User.class, id);
System.out.println("多态性读取成功：" + user);
session.getTransaction().commit();
success = true;
} finally {
if(session != null){
if(!success)
session.getTransaction().rollback();
session.close();
session = null;
}
}
}
} finally {
if(factory != null){
factory.close();
factory = null;
}
}
}
}
示例4：继承注解@Inheritance，继承策略InheritanceType.TABLE_PER_CLASS。
User.java
@Entity
@Table
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class User {
//---------------------------------------------------------------
// Field
//--------------------------------------------------------------- @Id
@Column(name = "id")
// 不能使用 GenerationType.IDENTITY，可以使用AUTO，或其它。
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator="genId")
@TableGenerator(
name = "genId",
table="GeneratorId",
pkColumnName="genName",
valueColumnName="genValue",
pkColumnValue="nextUserId",
allocationSize=1
)
private Long id; @Column(name = "loginName",
length = 20,
unique = true,
nullable = false,
updatable = false)
private String loginName; @Column(name = "loginPass",
length = 20,
nullable = false)
private String loginPass; //---------------------------------------------------------------
// Method
//--------------------------------------------------------------- public Long getId() {
return id;
} public void setId(Long id) {
this.id = id;
} public String getLoginName() {
return loginName;
} public void setLoginName(String loginName) {
this.loginName = loginName;
} public String getLoginPass() {
return loginPass;
} public void setLoginPass(String loginPass) {
this.loginPass = loginPass;
}
}
Admin.java
@Entity
@Table
public class Admin extends User {
@Column(name = "role", length = 20, nullable = false)
private String role; public String getRole() {
return role;
} public void setRole(String role) {
this.role = role;
}
}
Member.java
@Entity
@Table
public class Member extends User {
@Column(name = "name", length = 20, nullable = false)
private String name; public String getName() {
return name;
} public void setName(String name) {
this.name = name;
}
}
Test.java
public class Test {
public static void main(String[] params){
// 继承注解：@Inheritance
// 继承策略：InheritanceType.TABLE_PER_CLASS
// 公共属性独立表，独立属性独立表
new Test().test();
/*
Hibernate:
drop table if exists Admin
Hibernate:
drop table if exists GeneratorId
Hibernate:
drop table if exists Member
Hibernate:
drop table if exists User
Hibernate:
create table Admin (
id bigint not null,
loginName varchar(20) not null,
loginPass varchar(20) not null,
role varchar(20) not null,
primary key (id)
)
Hibernate:
create table GeneratorId (
genName varchar(255) not null,
genValue bigint,
primary key (genName)
)
Hibernate:
create table Member (
id bigint not null,
loginName varchar(20) not null,
loginPass varchar(20) not null,
name varchar(20) not null,
primary key (id)
)
Hibernate:
create table User (
id bigint not null,
loginName varchar(20) not null,
loginPass varchar(20) not null,
primary key (id)
)
Hibernate:
alter table Admin
add constraint UK_bdsh7mq6s6xad6ohm08u18uxr unique (loginName)
Hibernate:
alter table Member
add constraint UK_jxtse8o1c6l89j39lilw5e2rs unique (loginName)
Hibernate:
alter table User
add constraint UK_5iebj9qwxsnoshbaq6w834t0y unique (loginName)
Hibernate:
select
tbl.genValue
from
GeneratorId tbl
where
tbl.genName=? for update
Hibernate:
insert
into
GeneratorId
(genName, genValue)
values
(?,?)
Hibernate:
update
GeneratorId
set
genValue=?
where
genValue=?
and genName=?
Hibernate:
insert
into
Admin
(loginName, loginPass, role, id)
values
(?, ?, ?, ?)
Hibernate:
select
user0_.id as id1_2_0_,
user0_.loginName as loginNam2_2_0_,
user0_.loginPass as loginPas3_2_0_,
user0_.role as role1_0_0_,
user0_.name as name1_1_0_,
user0_.clazz_ as clazz_0_
from
( select
id,
loginName,
loginPass,
null as role,
null as name,
0 as clazz_
from
User
union
select
id,
loginName,
loginPass,
role,
null as name,
1 as clazz_
from
Admin
union
select
id,
loginName,
loginPass,
null as role,
name,
2 as clazz_
from
Member
) user0_
where
user0_.id=?
多态性读取成功：study.t4.Admin@12bf0e2
Hibernate:
drop table if exists Admin
Hibernate:
drop table if exists GeneratorId
Hibernate:
drop table if exists Member
Hibernate:
drop table if exists User
*/
}
public void test(){
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml", this.getClass());
SessionFactory factory = null;
try {
factory = (SessionFactory) context.getBean("sessionFactory");
// 多态性添加
boolean success = true;
Session session = null;
Long id = null;
try {
session = factory.openSession();
success = false;
session.beginTransaction();
User user = new Admin();
user.setLoginName("loginName");
user.setLoginPass("loginPass");
((Admin)user).setRole("role");
session.save(user);
session.getTransaction().commit();
id = user.getId();
success = true;
} finally {
if(session != null){
if(!success)
session.getTransaction().rollback();
session.close();
session = null;
}
}
// 多态性读取
if(success){
try {
session = factory.openSession();
session.beginTransaction();
success = false;
User user = session.load(User.class, id);
System.out.println("多态性读取成功：" + user);
session.getTransaction().commit();
success = true;
} finally {
if(session != null){
if(!success)
session.getTransaction().rollback();
session.close();
session = null;
}
}
}
} finally {
if(factory != null){
factory.close();
factory = null;
}
}
}
}
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