十六、继承映射

1    三种方式
a)    一张总表SINGLE_TABLE

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="discriminator", discriminatorType=DiscriminatorType.STRING)
@DiscriminatorValue("person")
public class Person {
    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;
    }

}

@Entity
@DiscriminatorValue("student")
public class Student extends Person {
   
    private int score;

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }
   
}

@Entity
@DiscriminatorValue("teacher")
public class Teacher extends Person {
    private String title;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

   
}

        create table Person (
        discriminator varchar(31) not null,
        id integer not null auto_increment,
        name varchar(255),
        score integer,
        title varchar(255),
        primary key (id)
    )

b)    每个类分别一张表TABLE_PER_CLASS

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
@TableGenerator(
        name="t_gen",
        table="t_gen_table",
        pkColumnName="t_pk",
        valueColumnName="t_value",
        pkColumnValue="person_pk",
        initialValue=1,
        allocationSize=1
        )
public class Person {
    private int id;
    private String name;
   
    @Id
    @GeneratedValue(generator="t_gen", 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;
    }

}

@Entity
public class Student extends Person {
   
    private int score;

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }
   
}

@Entity
public class Teacher extends Person {
    private String title;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

   
}

        create table Person (
        id integer not null,
        name varchar(255),
        primary key (id)
    )

    create table Student (
        id integer not null,
        name varchar(255),
        score integer not null,
        primary key (id)
    )

    create table Teacher (
        id integer not null,
        name varchar(255),
        title varchar(255),
        primary key (id)
    )

    create table t_gen_table (
         t_pk varchar(255),
         t_value integer
    )

c)    每个子类一张表jOINED

父类上加注解@Inheritance(strategy=InheritanceType.JOINED)
@Inheritance(strategy=InheritanceType.JOINED)

@Entity
@Inheritance(strategy=InheritanceType.JOINED)

public class Person {
    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;
    }

}

@Entity
public class Student extends Person {
   
    private int score;

    public int getScore() {
        return score;
    } //Person p = Person(load(1));

    public void setScore(int score) {
        this.score = score;
    }
   
}

@Entity
public class Teacher extends Person {
    private String title;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

   
}


    create table Person (
        id integer not null auto_increment,
        name varchar(255),
        primary key (id)
    )

    create table Student (
        score integer not null,
        id integer not null,
        primary key (id)
    )

    create table Teacher (
        title varchar(255),
        id integer not null,
        primary key (id)
    )

    alter table Student
        add index FKF3371A1BA6D67A60 (id),
        add constraint FKF3371A1BA6D67A60
        foreign key (id)
        references Person (id)

    alter table Teacher
        add index FKD6A63C2A6D67A60 (id),
        add constraint FKD6A63C2A6D67A60
        foreign key (id)
        references Person (id)

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