javax.persistence @JoinColumn 不工作

Question

I'm trying to join 2 tables (ManytoMany) and I'm getting this error:

Caused by: org.hibernate.AnnotationException: referencedColumnNames(planDate, planId, weekday) of com.MD.Medicine.Models.Meds.assignedMeds referencing com.MD.Medicine.Models.Plans not mapped to a single property

My entities, Plans.java:

@Data
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(name = "plans")
@EqualsAndHashCode(exclude = "assignedMeds")
public class Plans {
    @EmbeddedId
    private PlansPKId plansPKId;

    @Column
    private String planName;

    @Column
    private String weekday;

    @ManyToMany
    @JoinTable(name = "Plan_Meds", joinColumns = {
            @JoinColumn(name = "planDate", referencedColumnName = "planDate"),
            @JoinColumn(name = "planId", referencedColumnName = "planId"),
            @JoinColumn(name = "weekday", referencedColumnName = "weekday"), }, inverseJoinColumns = @JoinColumn(name = "id"))
    private Set<Meds> assignedMeds = new HashSet<>();

}

PlansPKId.java (for Plans Model):

@Data
@AllArgsConstructor
@NoArgsConstructor
@EqualsAndHashCode
@Embeddable
public class PlansPKId implements Serializable {

    private Date planDate; // format: yyyy-mm-dd
    private long planId;

  

}

Meds.java:

@Data
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(name = "meds")

public class Meds {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    @Column
    private String name;

    @Column
    private BigDecimal price;

    @Column
    private String category;

    @Column
    private int pillNumber;

    @Column
    private Date date;

    @JsonIgnore
    @ManyToMany(mappedBy = "assignedMeds")
    private Set<Plans> plans = new HashSet<>();

}

When I join only with this:

@ManyToMany
    @JoinTable(name = "Plan_Meds", joinColumns = {
            @JoinColumn(name = "planDate", referencedColumnName = "planDate"),
            @JoinColumn(name = "planId", referencedColumnName = "planId"), }, 
            inverseJoinColumns = @JoinColumn(name = "id"))
    private Set<Meds> assignedMeds = new HashSet<>();

It works properly, but if I had the column "weekday" I start getting the error. Am I not supposed to join them like that?

Answer 1

Yes, basically, the purpose of @JoinTable is to create an intermediate table that only contains keys of each participant table.

@ManyToMany
    @JoinTable(name = "Plan_Meds", joinColumns = {
            @JoinColumn(name = "planDate", referencedColumnName = "planDate"),
            @JoinColumn(name = "planId", referencedColumnName = "planId"),
            @JoinColumn(name = "weekday", referencedColumnName = "weekday"), }, inverseJoinColumns = @JoinColumn(name = "id"))
    private Set<Meds> assignedMeds = new HashSet<>();

In this case,

joinColumns = {
            @JoinColumn(name = "planDate", referencedColumnName = "planDate"),
            @JoinColumn(name = "planId", referencedColumnName = "planId")}

will refer to the key of your Plans entity plansPKId , and

inverseJoinColumns = @JoinColumn(name = "id")

will refer to the Meds entity's key id . Since weekday @JoinColumn(name = "weekday", referencedColumnName = "weekday") , it's not referring to any key, it should not be here.

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In case you need to add some more fields in the join table, manually create your own join table and use @ManyToOne instead: manytomany