I have a problem with Hibernate. I am using Spring 2.7.5. I have three entities.

• Alarm,
• AlarmList,
• ListAlarmJoinTable.

Alarm and AlarmList are in a MtoM relation. The tricky part is that they are not referencing each other, but they both have a OneToMany reference to the ListAlarmJoinTable.

Here are the classes:

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(name = "alarm")
public class Alarm {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private Integer alarmId;

    @Column(unique = true)
    String name;
    private Long time;
    private Integer code;
    private Integer priority;
    private String source;
    private String description;
    private String codeAsAsString;
    private String priorityAsString;
    private Integer dmId;
    private Boolean internal;
    private Integer instnaceindex;

    @OneToMany(orphanRemoval = true, cascade = {CascadeType.REMOVE, CascadeType.MERGE})
    private List<ListAlarmJoinTable> alarmLists;

    @Override
    public String toString() {
        return "JsonAlarm [time="   time   ", code="   code   ", priority="
                  priority   ", source="   source   ", description="
                  description   ", alarmId="   alarmId   ", codeAsAsString="
                  codeAsAsString   ", priorityAsString="   priorityAsString
                  ", dmId="   dmId   ", internal="   internal
                  ", instnaceindex="   instnaceindex   "]";
    }
}

@Entity
@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@ToString
@Table(name = "alarm_list")
public class AlarmList {

    @Id
    private String name;

    @OneToMany(orphanRemoval = true, cascade = {CascadeType.REMOVE, CascadeType.MERGE})
    private List<ListSequenceJoinTable> alarmSequences;

    @OneToMany(orphanRemoval = true, cascade = {CascadeType.REMOVE, CascadeType.MERGE})
    private List<ListAlarmJoinTable> alarms;

}

@Entity
@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@Table(name = "list_alarms_join_table")
public class ListAlarmJoinTable {

    @EmbeddedId
    private AlarmListId id;
    private int position;

}

@Embeddable
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class AlarmListId implements Serializable {

    private Integer alarmId;
    private String listId;

}

When Hibernate creates the schema and tables, it creates the following tables:

"alarm", "alarm_list", "alarm_alarm_lists" , "alarm_list_alarms", "list_alarms_join_table".

What I actually need are these: "alarm", "alarm_list", "list_alarms_join_table". Now, at first I thought it was the dialect, so I tried out every MySQL dialect and it didn't work. I even ran maven clean install (even though I knew that wouldn't change anything).

For further information this is my application.properties:

enter image description here

CodePudding user response：

The mapping is wrong because JPA cannot guess that ListAlarmJoinTable is essentially a join table (with an extra property). JPA sees your setup and thinks the relations Alarm → AlarmListId and AlarmList → AlarmListId have nothing to do with the fields of the AlarmListId, that you intended to be foreign keys.

Change the AlarmListId as follows to make the relation explicit:

@Embeddable
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class AlarmListId implements Serializable {
    @ManyToOne(optional=false, fetch=LAZY)
    private Alarm alarm;
    @ManyToOne(optional=false, fetch=LAZY)
    private AlarmList list;

    // You MUST implement hashCode() and equals(), probably Lombok's
    // @EqualsAndHashCode is enough but please check the semantics!!!
}

Now, you have to use mappedBy in the @OneToMany annotations over Alarm.alarmLists and AlarmList.alarms. I think the value should be:

    @OneToMany(..., mappedBy = "id.alarm")
    private List<ListAlarmJoinTable> alarmLists;

    // AND:

    @OneToMany(..., mappedBy = "id.list")
    private List<ListAlarmJoinTable> alarms;

The mappedBy property will help JPA understand that these are just the reverse sides of the same relation.