SpringDataJPA笔记(14)-Inheritance注解详解之SINGLE_TABLE

SpringDataJPA笔记(14)-Inheritance注解详解之SINGLE_TABLE

在JPA中使用映射注解Inheritance，有三种策略属性

SINGLE_TABLE – 将所有父类和子类集合在一张表

TABLE_PER_CLASS – 每个子类会生成一张单独的表，父类可以查询所有子类的表数据，参考上一篇笔记Union查询

JOINED – 每个类分别生成一张单独的表，但是每张表只有自己的属性，没有父类的属性，通过外键关联的形式使两张表关联起来

public enum InheritanceType { 

    /** A single table per class hierarchy. */
    SINGLE_TABLE, 

    /** A table per concrete entity class. */
    TABLE_PER_CLASS, 

    /** 
     * A strategy in which fields that are specific to a 
     * subclass are mapped to a separate table than the fields 
     * that are common to the parent class, and a join is 
     * performed to instantiate the subclass.
     */
    JOINED 
}

简单写个demo测试一下

分别新建三个实体类

@Data
@Table(name = "inheritance_single_tb")
@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class InheritanceSingleEntity implements Serializable {
    private static final long serialVersionUID = 8139674112977338603L;

    @Id
    private Long id;

    @Column(name = "single_name")
    private String singleName;
}

@Data
@Entity
@EqualsAndHashCode(callSuper = true)
@Table(name = "inheritance_single_one_tb")
public class InheritanceSingleOneEntity extends InheritanceSingleEntity{

    private static final long serialVersionUID = 9042160117012026124L;

    @Column(name = "single_one")
    private String singleOne;
}

@Data
@Entity
@EqualsAndHashCode(callSuper = true)
@Table(name = "inheritance_single_two_tb")
public class InheritanceSingleTwoEntity extends InheritanceSingleEntity {

    private static final long serialVersionUID = 9042160117012026124L;

    @Column(name = "single_two")
    private String singleTwo;
}

再新建三个repository接口类

public interface InheritanceSingleRepository extends JpaRepository, JpaSpecificationExecutor, Serializable {
}

public interface InheritanceSingleOneRepository extends JpaRepository, JpaSpecificationExecutor, Serializable {
}

public interface InheritanceSingleTwoRepository extends JpaRepository, JpaSpecificationExecutor, Serializable {
}

新建一个controller类用于测试数据情况

@RestController
@RequestMapping("/chapter/inheritances")
public class ChapterInheritanceController {

    @Autowired
    private InheritanceSingleRepository inheritanceSingleRepository;

    @Autowired
    private InheritanceSingleOneRepository inheritanceSingleOneRepository;

    @Autowired
    private InheritanceSingleTwoRepository inheritanceSingleTwoRepository;

    @PostMapping("/single")
    public InheritanceSingleEntity single(@RequestBody InheritanceSingleEntity inheritanceSingleEntity){
        return inheritanceSingleRepository.save(inheritanceSingleEntity);
    }

    @PostMapping("/single/one")
    public InheritanceSingleOneEntity single(@RequestBody InheritanceSingleOneEntity inheritanceSingleEntity){
        return inheritanceSingleOneRepository.save(inheritanceSingleEntity);
    }

    @PostMapping("/single/two")
    public InheritanceSingleTwoEntity single(@RequestBody InheritanceSingleTwoEntity inheritanceSingleEntity){
        return inheritanceSingleTwoRepository.save(inheritanceSingleEntity);
    }

    @GetMapping("/single")
    public List single(){
        return inheritanceSingleRepository.findAll();
    }

    @GetMapping("/single/one")
    public List singleOne(){
        return inheritanceSingleOneRepository.findAll();
    }

    @GetMapping("/single/two")
    public List singleTwo(){
        return inheritanceSingleTwoRepository.findAll();
    }
}

此时查看数据库，看到生成了一张表

查看表结构，发现有三张表的字段同时存在

这里还有一个dtype的字段，这个是默认的区别的字段名，还可以用@DiscriminatorColumn加@DiscriminatorValue的注解来指定

在swagger页面分别通过三个接口创建三条数据，查看表数据

例如加上@DiscriminatorColumn加@DiscriminatorValue的注解

@Data
@Table(name = "inheritance_single_tb1")
@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "single_type", discriminatorType = DiscriminatorType.STRING)
@DiscriminatorValue(value = "base")
public class InheritanceSingleEntity implements Serializable {
    private static final long serialVersionUID = 8139674112977338603L;

    @Id
    private Long id;

    @Column(name = "single_name")
    private String singleName;
}

@Data
@Entity
@EqualsAndHashCode(callSuper = true)
@Table(name = "inheritance_single_one_tb")
@DiscriminatorValue(value = "one")
public class InheritanceSingleOneEntity extends InheritanceSingleEntity{

    private static final long serialVersionUID = 9042160117012026124L;

    @Column(name = "single_one")
    private String singleOne;
}

@Data
@Entity
@EqualsAndHashCode(callSuper = true)
@Table(name = "inheritance_single_two_tb")
@DiscriminatorValue(value = "two")
public class InheritanceSingleTwoEntity extends InheritanceSingleEntity {

    private static final long serialVersionUID = 9042160117012026124L;

    @Column(name = "single_two")
    private String singleTwo;
}

写入三条数据之后查看数据库

再通过查询接口查询数据

可以看到通过父类查询可以查询所有数据，而子类只能分别查询出子类的数据

欢迎关注微信交流