Kotlin Hibernate @ManyToOne MERGE 违反外键约束 (Postgres)

Question

我实现了一个@ModelToOne 关系，并想通过 Thymeleaf 使用下拉列表。我使用单独的公式来保存 PlaceEntities，并使用公式来保存 WorkEntities，其中可以从提到的下拉列表中选择适当的地点。当前的实现强制我添加一个 Place，否则将不会保留 WorkEntity。当我尝试在未从下拉列表中选择地点的情况下保存表单时，出现以下错误：

ERROR: insert or update on table "work" violates foreign key constraint "fklyi06ir16ujsbylbtf5k33rmv" Detail: Key (place_of_premiere_id)=() is not present in table "place".

我已经尝试将“optional = true”条件（在任何情况下默认情况下都是 true）或 @JoinColumn(nullable = true) 添加到 @ManyToOne Side，但是 none 这些都有效。

保存带有选定地点的表单非常有效，但是如果我想保留一个没有 PlaceEntity 的 WorkEntity（这意味着外键列必须为空），我该如何做到这一点？

编辑：我可以自己解决这个问题。错误来自模板第一个选项标签中的 th:value=""。它创建了一个不能持久化的零参数 Object 而不是 null。我在我的控制器中放置了一个 if 语句，这可能不是最优雅的方法，但我不知道如何在 Thymeleaf 中使 th:value= 可为空。

我的固定控制器：

@PostMapping(value = ["/addWork"])
fun addWork(@Validated work: Work?, bindingResult: BindingResult): String {
    if (bindingResult.hasErrors()) {
        print(bindingResult.allErrors)
    }
    
    work?.apply {

        if (placeOfPremiere?.id == "") {
            this.placeOfPremiere = null
        }
    }

    workService.create(work!!)
    return "editor/addWork"
}

所有实体的摘要 class：

@MappedSuperclass
abstract class Entity(
    @Id
    @GeneratedValue(generator = "system-uuid")
    @GenericGenerator(name = "system-uuid", strategy = "uuid")
    open var id: String?,
    open var title: String?,
    open var created: OffsetDateTime,
    open var modified: OffsetDateTime

Child:

     @Entity
     @Table(name = "work")
     class WorkEntity(
             id: String? = null,
             title: String? = null,
             created: OffsetDateTime = OffsetDateTime.now(),
             modified: OffsetDateTime = OffsetDateTime.now(),
             var opus: String? = null,
             var dateOfCreation: String? = null,
             var dateOfPremiere: String? = null,

      @JsonManagedReference
      @ManyToOne(
            fetch = FetchType.LAZY,
            cascade = [CascadeType.MERGE]
       ) 
      var placeOfPremiere: PlaceEntity? = null,

      ...Other Properties...equals...hashcode...

Parent:

      @Entity
      @Table(name = "place")
      class PlaceEntity(
              id: String? = null,
              title: String? = null,
              created: OffsetDateTime = OffsetDateTime.now(),
              modified: OffsetDateTime = OffsetDateTime.now(),
              var name: String? = null,
              var locality: String? = null,
              var country: String? = null,

              @Embedded
              @AttributeOverrides(
                  AttributeOverride(name = "latitude", column = Column(name = "latitude")),
                  AttributeOverride(name = "longitude", column = Column(name = "longitude"))
              )
              var coordinates: CoordinatesEntity? = CoordinatesEntity(),

              @JsonBackReference
              @OneToMany(mappedBy = "placeOfPremiere")
              var relatedWorks: MutableSet<WorkEntity>? = mutableSetOf()              
              ...Other Properties...equals...hashcode...

我的 ThymeleafTemplate 的下拉菜单：

                <div class="form-group">
                    <label for="places">Places</label>
                    <select th:field="*{placeOfPremiere.id}" class="form-control" id="places"
                            name="Place of Premiere">
                        <option th:value="">Select Places</option>
                        <option
                                th:each="place : ${places}"
                                th:value="${place.id}"
                                th:text="${place.title}">
                        </option>
                    </select>
               <span th:if="${#fields.hasErrors('placeOfPremiere')}" th:errors {placeOfPremiere}"></span>
                 </div>

Answer 1

我想问题是 Work 实体指的是一个尚不存在的 Place。要么将外键标记为 deferrable initially deferred，要么确保调用 persist 或 merge 的顺序正确。

Kotlin Hibernate @ManyToOne MERGE 违反外键约束 (Postgres)

Kotlin Hibernate @ManyToOne MERGE violates foreign key constraint (Postgres)

hibernate

kotlin

thymeleaf

many-to-one

constraintviolationexception