java - 我如何像在MySQL中那样在Spring Boot JPA中建立一对多关系？

Question

这是我的课

@Entity
@Table(name = "player", catalog = "leaderboard")
public class Player {
@Id
@Column(name = "player")
private String player;

@Column(name = "claim")
private Integer claim;

@Column(name = "fraud_score")
private Double fraudScore;

@Column(name = "fraud_value")
private String fraudValue;

@Column(name = "expected_claim")
private Double expectedClaimCost;

@Column(name = "expected_rpa")
private Double expectedRpaCost;

@Column(name = "accident_date")
private String accidentDate;

@Column(name = "submission_time")
private LocalTime submissionTime;

@OneToMany
@JoinColumn(name = "claim", referencedColumnName = "claim", insertable = false, updatable = false)
private ExpectedClaim expectedClaim;
// removed getters and setters for brevity

和

@Entity
@Table(name = "expected_claim", catalog = "leaderboard")
public class ExpectedClaim {

@Id
@Column(name = "claim")
private Integer claim;

@Column(name = "fraud_score")
private Double fraudScore;

@Column(name = "fraud_value")
private String fraudValue;

@Column(name = "expected_claim")
private Double expectedClaim;

@Column(name = "expected_rpa")
private Double expectedRpa;
// removed getters and setters for brevity

现在我们在MYSQL中有一个外键概念
其中表格Expected_claim和player与“ claim”列具有父子关系。

所以我刚开始使用Spring JPA
并试图了解一对多，多对一，多对多和一对一的工作原理，但无法获得我想要的东西，或者您可以说无法理解它们的实际实现方式。

我尝试在此处使用“一对多”将Player（子级）连接到ExpectedClaim（父级）。

但是我不明白的是，在MYSQL中，您只需要输入如下数据

insert into player values("Abc",1234,98,"Not Fraud",2500,2700,"31/12/2019","12:00:00")

如果Expect_claim表中存在任何Claim（第二列），则将插入记录，否则将不会插入。

但在这儿，
我看了很多关于这些关系的视频，但无法了解我们如何在这里做到这一点？
每次创建播放器时，我都必须创建一个Expected_claim对象吗？

Answer 1

您几乎明白了，这是您必须修复的仅有两件事。
如果我对您的理解正确，那么您希望某个声明具有多个玩家，而一个玩家具有单个声明。


  1）将@ManyToOne注释添加到您对玩家的预期要求中

@Entity
@Table(name = "player", catalog = "leaderboard")
public class Player {
    @Id
    @Column(name = "player")
    private String player;

    @Column(name = "claim")
    private Integer claim;

    @Column(name = "fraud_score")
    private Double fraudScore;

    @Column(name = "fraud_value")
    private String fraudValue;

    @Column(name = "expected_claim")
    private Double expectedClaimCost;

    @Column(name = "expected_rpa")
    private Double expectedRpaCost;

    @Column(name = "accident_date")
    private String accidentDate;

    @Column(name = "submission_time")
    private LocalTime submissionTime;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "claim", referencedColumnName = "claim", insertable = false, updatable = false)
    private ExpectedClaim expectedClaim;
}

  2）在您的预期声明中添加@OneToMany批注。

@Entity
@Table(name = "expected_claim", catalog = "leaderboard")
public class ExpectedClaim {

    @Id
    @Column(name = "claim")
    private Integer claim;

    @Column(name = "fraud_score")
    private Double fraudScore;

    @Column(name = "fraud_value")
    private String fraudValue;

    @Column(name = "expected_claim")
    private Double expectedClaim;

    @Column(name = "expected_rpa")
    private Double expectedRpa;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "expectedClaim")
    private Collection<Player> players;

    // removed getters and setters for brevity
}

在这种情况下，Player将是您提到的Player(child)关系的所有者，并将在其表中包含其引用的列。