[英]Cannot add or update a child row: a foreign key constraint fails error when trying to save an entity and its relational entity
[英]Unable to save an entity "a foreign key constraint fails "
我正在嘗試將實體保存到使用 @JoinTable 注釋創建的表中。
這是設置表的主要實體:
public class MachineGroup {
@Id
@GeneratedValue(strategy= GenerationType.AUTO, generator = "machine_groups_seq")
@SequenceGenerator(name = "machine_groups_seq", allocationSize = 1, initialValue = 2)
@Column(name = "id")
private long id;
@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(name = "machine_groups_to_machines",
joinColumns = @JoinColumn(name = "machine_group_id"),
inverseJoinColumns = @JoinColumn(name = "machine_id"))
private Set<Machine> machines;
}
我嘗試保存的實體:
@Entity
@Table(name="machine_groups_to_machines")
@Getter
@Setter
public class MachineGroupToMachine {
@Id
@GeneratedValue(strategy= GenerationType.IDENTITY)
@Column(name = "id")
private long id;
@ManyToOne
@JoinColumn(name = "machine_id")
private Machine machine;
@ManyToOne
@JoinColumn(name = "machine_group_id")
private MachineGroup machineGroup;
public MachineGroupToMachine(Machine machine, MachineGroup machineGroup) {
this.machine = machine;
this.machineGroup = machineGroup;
}
}
現在我試圖通過 MachineGroupToMachineRepository 直接使用這個保存 MachineGroupToMachine :
public MachineGroup save(Machine machine, MachineGroup machineGroup){
Optional<MachineGroupToMachine> omgm = machineGroupToMachineRepository.findMachineGroupToMachineByMachineAndMachineGroup(machine, machineGroup);
if(omgm.isPresent()){
String names = MessageFormat.format("Machine {0} and Machine Group {1}", machine.getName(), machineGroup.getName());
throw new EntityAlreadyExistsException(names);
}
return machineGroupToMachineRepository.save(new MachineGroupToMachine(machine, machineGroup)).getMachineGroup();
}
Hibernate 嘗試執行此查詢:
Hibernate: insert into machine_groups_to_machines (machine_id, machine_group_id) values (?, ?)
這是例外:
Cannot add or update a child row: a foreign key constraint fails (`test_db`.`machine_groups_to_machines`, CONSTRAINT `FK7g1k7n6hssjrwqadtrx0pc840` FOREIGN KEY (`MACHINE_ID`) REFERENCES `machines` (`id`))
我是否以適當的方式保存實體? 也許應該從其他地方完成?
你不明白的是什么? 您指的是此MachineGroupToMachine
實體中的一台機器,該機器在數據庫中不存在(還?)。 如果你還想保留機器,那么你將不得不在機器關聯上使用@ManyToOne(cascade = PERSIST)
,但我懷疑這是你通常想要的。 所以在你堅持MachineGroupToMachine
之前堅持機器。
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