Question

我有两张由FK关联的表。

表学生的映射方式如下：

@Entity
@Table(name="student")
public class Student implements Serializable {
  ...
  @Id
  @GeneratedValue
  private int id; 

  @ManyToOne(fetch = FetchType.LAZY, optional = true) 
  @JoinColumn(name = "school_ID", nullable = true, insertable = false, updatable = false)
  private School school;

  private Integer school_ID; 

  @Transient
  private boolean editable = false;
}

表学校：

@Entity
@Table(name="school")
public class School implements Serializable {
  ...
  @OneToMany(fetch = FetchType.LAZY, mappedBy = "school")
  private Set<Student> student = new HashSet<Student>(0);

当我尝试插入/更新不在任何学校（student.school_ID is null）的学生时，它会报告：

Exception: java.lang.Exception: org.hibernate.exception.ConstraintViolationException:
could not update: [tables.Student#556758]
...
Caused by: com.microsoft.sqlserver.jdbc.SQLServerException: The UPDATE statement
conflicted with the FOREIGN KEY constraint "FK__student__school_ID__57378E7F". The 
conflict occurred in database "DB", table "dbo.school", column 'id'.

我是否有可能在FK上插入null值？

我要定义它：

实体级别或
数据库级别？

更新：

我已更改private School school = new School()，但当我尝试插入/更新行时，它仍会报告：

SEVERE: Servlet.service() for servlet [Faces Servlet] in context with path [/DB] threw exception [javax.el.PropertyNotFoundException: /view.xhtml @183,102 value="#{item.school.id}": Target Unreachable, 'school' returned null] with root cause
javax.el.PropertyNotFoundException: /view.xhtml @183,102 value="#{item.school.id}": Target Unreachable, 'school' returned null

view.xhtml：

<rich:column>
  <h:outputText value="#{item.school != null ? item.school.name : null}" rendered="#{!item.editable}"/>
  <h:selectOneMenu id="som" tabindex="1" value="#{item.school.id}"  rendered="#{item.editable}">
    <f:selectItems value="#{myDials.schoolList}"/> 
  </h:selectOneMenu>
</rich:column>
<rich:column>

Answer 1

您在同一school_id列上映射了两个不同的字段：

private School school;
private Integer school_ID;

删除school_ID字段。您不需要它，因为您已经与学校实体建立了关联。

并从关联映射中删除insertable = false, updatable = false。您应该使用school字段来创建，更新或删除关联。

hibernate - 在FK上允许null值

1 个答案: