Question

我正在尝试绘制一个有多场比赛的比赛日，并且无法找出注释。

我最终想要的是（这是一个简化的例子）：

TABLE: race_day
    date (PK)
    venue (PK)
    description

TABLE: race
    date (PK but also FK on race_day table)
    venue (PK but also FK on race_day table)
    race_number (PK)
    description

到目前为止，我已经提出了以下POJO +注释：

public class RaceDayPK implements Serializable {

    @Column(name="race_date")
    private String raceDate;
    @Column(name="venue")
    private String venue;
...
}

public class RaceDay {

    @EmbeddedId
    private RaceDayPK raceDayPk;

    @OneToMany(mappedBy = "raceDay", orphanRemoval = true, cascade = {CascadeType.ALL}, fetch = FetchType.EAGER)
    private final List<Race> races = new ArrayList<>();

...
}

public class Race {

    @ManyToOne
    @JoinColumns({
        @JoinColumn(name = "race_date", referencedColumnName = "race_date"),
        @JoinColumn(name = "venue", referencedColumnName = "venue")
    })
    private RaceDay raceDay;

    private int raceNumber;
    private String raceTitle;
...
}

我如何使用raceDay连接列和raceNumber为Race制作EmbeddedId（我猜这是我需要的）？任何帮助赞赏。我在StackOverflow上看到过几十个JoinColumn示例和EmbeddedId示例，但似乎没有一个以我需要的方式将两者结合起来。

Answer 1

经过一番黑客攻击后，我认为我得到了这样的工作。请注意OneToMany批注的mappedBy参数中嵌套的“racePk.raceMeeting”：

public class RaceDayPK implements Serializable {

    @Column(name="race_date")
    private String raceDate;
    @Column(name="venue")
    private String venue;
...
}


public class RaceDay {

    @EmbeddedId
    private RaceDayPK raceDayPk;

    @OneToMany(mappedBy = "racePk.raceDay", orphanRemoval = true, cascade = {CascadeType.ALL}, fetch = FetchType.EAGER)
    private final List<Race> races = new ArrayList<>();

...
}


public class RacePk implements Serializable {

    @ManyToOne
    @JoinColumns({
        @JoinColumn(name = "race_date", referencedColumnName = "race_date"),
        @JoinColumn(name = "venue", referencedColumnName = "venue")
    })
    private RaceDay raceDay;
    @Column(name = "race_number")
    private int raceNumber;
...
}


public class Race {

    @EmbeddedId
    private final RacePk racePk = new RacePk();
    private String raceTitle;
...
}

不知道这是否会在某些时候失败，但MySQL表似乎是自动生成的。

Answer 2

TABLE: race_day
        id(PK)
        date (PK)
        venue (PK)
        description

TABLE: race
        id(PK but also FK on race_day table)
        date (PK but also FK on race_day table)
        venue (PK but also FK on race_day table)
        race_number (PK)
        description

对于上面给定的表，我可以使用以下代码生成序列并按照约束将数据持久保存在表中。

    public class RaceDayPK implements Serializable {

        private Long id;
        private String raceDate;
        private String venue;
    ...
    }

    @Entity
    @IdClass(RaceDayPK.class)
    public class RaceDay {

        @Id
        @Column(name="id")
        @GeneratedValue(strategy=GenerationType.SEQUENCE,generator = "R_SEQ")
        @SequenceGenerator(sequenceName = "RD_SEQ", allocationSize = 1, name = "R_SEQ")
        private Long id;

        @Id
        @Column(name="race_date")
        private String raceDate;

        @Id
        @Column(name="venue")
        private String venue;

        @OneToMany(mappedBy = "raceDay", cascade = {CascadeType.ALL}, fetch = FetchType.LAZY)
        private Set<Race> races;

    ...
    }

    public class RacePK implements Serializable {


        private RaceDay raceDay;
        private int raceNumber;
    ...
    }

    @Entity
    @IdClass(RacePK.class)
    public class Race {

        @Id
        @ManyToOne(cascade = CascadeType.ALL)
        @JoinColumns({
            @JoinColumn(name = "race_date", referencedColumnName = "race_date"),
            @JoinColumn(name = "venue", referencedColumnName = "venue"),
            @JoinColumn(name = "id", referencedColumnName = "id")
        })
        @JsonIgnore
        private RaceDay raceDay;

        @Id
        private int raceNumber;

        private String raceTitle;
    ...
    }

下面需要对dao代码进行一些更改。

public RaceDay saveRaceDay(RaceDay raceDay){
 if(raceDay.getRaces()!=null){
            raceDay.getRaces().forEach(race ->{
                race.setRaceDay(raceDay);
            });
        }
        }

Answer 3

不确定它是否有效但尝试这种方法：

public class RacePK implements Serializable {

    private RaceDayPK raceDay;    
    private String raceNumber;
...
}

@Entity
@IdClass(RacePK.class)
public class Race {

    @Id 
    @ManyToOne...
    private RaceDay raceDay;

    @Id
    private int raceNumber;
    private String raceTitle;
...
}

请注意，PK字段名称应与@ id-annotaed字段名称完全相同。 Google for Derived标识符可了解详情。

父组合键的JPA注释是子组合主键的一部分

3 个答案: