休眠 - 在FK上允許空值

表學生映射這樣的：

@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; 
}

表學校：

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

當我嘗試插入/更新的學生，這是不以任何學校（student.school_ID is null ）它報告：

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'.

我也有可能在FK上插入null值嗎？

要不要我把它定義上：

實體級別或
數據庫級別？

UPDATE：

我已經改變private School school = new School()，但是當我嘗試插入/更新行，但它仍然報道：

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>

來源

2012-06-14 gaffcz

您映射了兩個不同的字段school_id column：

private School school; 
private Integer school_ID;

刪除school_ID字段。你不需要它，因爲你已經與學校實體有聯繫。

並且還從關聯映射中移除insertable = false, updatable = false。您應該使用school字段來創建，更新或刪除關聯。

來源

2012-06-14 11:03:35

再次感謝您。它似乎更好，但是當我嘗試更新選定的項目時，它會報告nullPointerException（請參閱我的更新問題） – gaffcz

但是，實際上，表格學生只有'姓名'，'姓氏'，'年齡'和'school_id'列。沒有行類型列... – gaffcz

更新與JSF相關，我對JSF一無所知。 –

休眠 - 在FK上允許空值

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