Question

我是一个休眠的新家伙。假设有两个表T1和T2，其中T1的主键值也用作T2的主键。对于T2中的每一行，T1中应该有一个对应的行，但反之则不一定是真的。这是一对一的映射吗？

Answer 1

这将被称为使用shared primary key的一对一映射。

以下是如何将关系映射到两个实体（州和资本）的示例。

<强>表格

CREATE TABLE `capital` (
  `CAPITAL_ID` bigint(20) NOT NULL AUTO_INCREMENT,
  `NAME` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`CAPITAL_ID`),
  CONSTRAINT `STATE_ID` FOREIGN KEY (`CAPITAL_ID`) REFERENCES `state` (`STATE_ID`) ON DELETE NO ACTION ON UPDATE NO ACTION
);

CREATE TABLE `state` (
  `STATE_ID` bigint(20) NOT NULL AUTO_INCREMENT,
  `NAME` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`STATE_ID`)
);

<强>国家

@Entity
@Table(name = "STATE")
public class State {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "STATE_ID")
    private Long stateId;

    @Column(name = "NAME")
    private String name;

    @OneToOne(cascade = CascadeType.ALL, mappedBy = "state")
    private Capital capital;

    public Long getStateId() {
        return stateId;
    }

    public Capital getCapital() {
        return capital;
    }

    public void setCapital(Capital capital) {
        this.capital = capital;
    }

    public void setStateId(Long stateId) {
        this.stateId = stateId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

<强>资本

@Entity
@Table(name = "CAPITAL")
public class Capital {

    @Id
    @Column(name = "CAPITAL_ID")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long capitalId;

    @Column(name = "NAME")
    private String name;

    @OneToOne
    @PrimaryKeyJoinColumn
    private State state;

    public State getState() {
        return state;
    }

    public void setState(State state) {
        this.state = state;
    }

    public Long getCapitalId() {
        return capitalId;
    }

    public void setCapitalId(Long capitalId) {
        this.capitalId = capitalId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

示例

public class HibernateApplication { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); SessionFactory factory = null; Session session = null; org.hibernate.Transaction tx = null; try { factory = HibernateUtil.getSessionFactory(); session = factory.openSession(); tx = session.beginTransaction(); State state = new State(); Capital capital = new Capital(); state.setName("Pennsylvania"); capital.setName("Harrisburg"); state.setCapital(capital); capital.setState(state); session.save(state); tx.commit(); } catch (Exception e) { e.printStackTrace(); tx.rollback(); } finally { session.close(); factory.close(); scanner.close(); } } }

在hibernate中，Can实体是否在一对一映射中不存在映射？

1 个答案: