问题描述
我实现了@ModelToOne关系,并希望通过Thymeleaf使用下拉列表。我使用一个单独的公式来保存PlaceEntities,并使用WorkEntities的公式来从上面提到的下拉列表中选择一个合适的Place。当前的实现迫使我添加一个Place,否则WorkEntity将不会保留。当我尝试保存表单而未从下拉列表中选择位置时,出现以下错误:
错误:在表“工作”上进行插入或更新违反了外键约束“ fklyi06ir16ujsbylbtf5k33rmv” 详细信息:表(place)中不存在键(place_of_premiere_id)=()。
我已经尝试在@ManyToOne端添加“可选= true”条件(无论如何默认情况下为true)或@JoinColumn(nullable = true),但这些都不起作用。
使用选定的位置保存表单就像一个超级按钮一样,但是如果我要保留一个没有PlaceEntity的WorkEntity(这意味着外键列必须为null),该怎么办?
编辑: 我可以自己解决这个问题。错误来自模板的第一个选项标签中的th:value =“”。它创建一个零参数而不是null,而不是null,它不能持久保存。我在控制器中放入了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"
}
所有实体的抽象类:
@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
孩子:
@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...
父母:
@Entity
@Table(name = "place")
class PlaceEntity(
id: String? = null,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>
解决方法
我想问题是Work
实体指向尚不存在的Place
。您可以将外键标记为deferrable initially deferred
或确保调用persist
或merge
的顺序正确。