如何告诉JPA管理依赖实体

Question

我的模型有一个典型的父子关系，它是由单向@OneToMany关系建模的JPA：
Parent有0..n个Child实例(即List<Child>(。

尝试创建并持久化具有一个依赖Property的Entity，如下所示：

val a_parent = Parent(
id = "I_am_a_parent",
children = listOf(Child(kind="childish"))
)
parentRepository.save(a_parent)

的惊人结果

org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [parent_id]; nested exception is 
...
Caused by: org.postgresql.util.PSQLException: 
ERROR: null value in column "parent_id" violates not-null constraint
Detail: Failing row contains (22, childish, null).

在线路CCD_ 7处。

显然，JPA不会在子项(列children.parent_id(上设置父项的id。

为什么不呢？如何告诉它这样做

Parent和Child的代码如下

@Entity
@Table(name = "parents")
data class Parent (
@Id
@Column(name = "id")
var id: String? = null,
@OneToMany(cascade = [CascadeType.ALL], orphanRemoval = true)
@JoinColumn(name = "parent_id")
var properties: List<Child> = listOf()
)

@Entity
@Table(name = "children")
data class Child (
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
var id: Int? = null,
@Column(name = "kind")
var kind: String? = null
)

Answer 1

单向OneToMany可能必须以这种方式实现(参考(：

data class Parent (
//...
@OneToMany(cascade = [CascadeType.ALL], orphanRemoval = true)
@JoinColumn(name = "parent_id", nullable = false)
var properties: List<Child> = listOf()
)

如果数据库列parent_id不可为null，请注意nullable = false。