hibernate继承映射 

以下测试是在mysql中进行的。 

1、单表方式 

Animal.java 

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="animalType")
@DiscriminatorValue("animal")
public class Animal {
    private int id;
    private String name;

    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Cat.java 

@Entity
@DiscriminatorValue("cat")
public class Cat extends Animal {

    private String catName;

    public String getCatName() {
        return catName;
    }
    public void setCatName(String catName) {
        this.catName = catName;
    }
}

Dog.java 

@Entity
@DiscriminatorValue(value="dog")
public class Dog extends Animal{
    private String dogName;

    public String getDogName() {
        return dogName;
    }
    public void setDogName(String dogName) {
        this.dogName = dogName;
    }
}

TestJunit.java 

@Test
public void testAnimal(){
    Animal t = new Animal();
    t.setName("animal");
    session.saveOrUpdate(t);
}

@Test
public void testCat(){
    Cat t = new Cat();
    t.setName("cat");
    t.setCatName("cat");
    session.saveOrUpdate(t);
}

@Test
public void testDog(){
    Dog t = new Dog();
    t.setName("dog");
    t.setDogName("dog");
    session.saveOrUpdate(t);
}

对应生成的数据表是这样的 

table---animal 

id	name	animalType	catName	dogName
1	animal	animal	null	null
2	cat	cat	cat	null
3	dog	dog	null	dog

2、join方式 

Animal.java 

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class Animal {
    private int id;
    private String name;

    @Id
    @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Cat.java 

@Entity
@PrimaryKeyJoinColumn(name="catId")
public class Cat extends Animal {

    private String catName;

    public String getCatName() {
        return catName;
    }
    public void setCatName(String catName) {
        this.catName = catName;
    }
}

Dog.java 

@Entity
@PrimaryKeyJoinColumn(name="dogId")
public class Dog extends Animal{
    private String dogName;

    public String getDogName() {
        return dogName;
    }
    public void setDogName(String dogName) {
        this.dogName = dogName;
    }
}

TestJunit.java 

@Test
public void testAnimal(){
    Animal t = new Animal();
    t.setName("animal");
    session.saveOrUpdate(t);
}

@Test
public void testCat(){
    Cat t = new Cat();
    t.setName("cat");
    t.setCatName("cat");
    session.saveOrUpdate(t);
}

@Test
public void testDog(){
    Dog t = new Dog();
    t.setName("dog");
    t.setDogName("dog");
    session.saveOrUpdate(t);
}

对应生成的数据表是这样的 

table---Animal 

id	name
1	animal
2	cat
3	dog

table---cat 

catId	catName
2	cat

table---dog 

dogId	dogName
3	dog

3、每个实体类对应一个数据表 

以下的测试中，Anamal.java中的主键生成策略需要注解成@GeneratedValue(strategy=GenerationType.TABLE)，测试是在mysql数据库中进行的。 

Animal.java 

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public class Animal {
    private int id;
    private String name;

    @Id
    @GeneratedValue(strategy=GenerationType.TABLE)
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Cat.java 

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public class Cat extends Animal {

    private String catName;

    public String getCatName() {
        return catName;
    }
    public void setCatName(String catName) {
        this.catName = catName;
    }
}

Dog.java 

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public class Dog extends Animal{
    private String dogName;

    public String getDogName() {
        return dogName;
    }
    public void setDogName(String dogName) {
        this.dogName = dogName;
    }
}

TestJunit.java 

@Test
public void testAnimal(){
    Animal t = new Animal();
    t.setName("animal");
    session.saveOrUpdate(t);
}

@Test
public void testCat(){
    Cat t = new Cat();
    t.setName("cat");
    t.setCatName("cat");
    session.saveOrUpdate(t);
}

@Test
public void testDog(){
    Dog t = new Dog();
    t.setName("dog");
    t.setDogName("dog");
    session.saveOrUpdate(t);
}

对应生成的数据表是这样的 

table---animal 

id	name
1	animal

table---cat 

id	name	catName
2	cat	cat

table---dog 

id	name	dogName
3	dog	dog