Question

将Hibernate 5用作ORM。

我认为optional=true意味着列可以保存空值。

我有两个实体 - ：

选修
ElectivePractical

选修课可能与ElectivePractical相关或不相关，但ElectivePractical必须始终与选修课相关联。

Elective.java

public class Elective extends Theory {

    private static final long serialVersionUID = 1L;

    @Column (name = "ELEC_NO", 
            table = "ELECTIVES", 
            length = 3)
    private String electiveNo;

    @OneToOne (targetEntity = ElectivePractical.class,
            mappedBy = "elective",
            fetch = FetchType.EAGER,
            cascade = CascadeType.ALL,
            optional = true)
    private ElectivePractical practical;

    @ManyToMany(targetEntity = Student.class, 
            fetch = FetchType.EAGER,
            mappedBy = "electives")
    private Collection<Student> students = new ArrayList<>();

ElectivePractical.java

public class ElectivePractical extends Practical {

    private static final long serialVersionUID = 1L;

    @OneToOne (targetEntity = Elective.class,
            fetch = FetchType.EAGER,
            cascade = CascadeType.MERGE)
    @JoinTable (name = "ELECTIVE_PRACTICAL",
            joinColumns = @JoinColumn (name = "ELEC_PRAC_ID",
            referencedColumnName = "ID", nullable = false), 
            inverseJoinColumns = 
            @JoinColumn (name = "ELEC_THEORY_ID",
            referencedColumnName = "ID", nullable = false))
    private Elective elective;

您可以看到ElectivePractical中的Elective.java设置为optional=true

然而，当我尝试merge()一个没有实际意义的选修实例时，我得到以下错误 - ：

javax.persistence.PersistenceException: org.hibernate.PropertyValueException: not-null property references a null or transient value : com.sts.entity.subjects.Elective.practical
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1692)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1602)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1608)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:1171)
    at com.sts.persistence.STSDao.addCourse(STSDao.java:250)
    at com.sts.validators.CourseValidator.commit(CourseValidator.java:558)
    at test.main.CourseTest.main(CourseTest.java:27)
Caused by: org.hibernate.PropertyValueException: not-null property references a null or transient value : com.sts.entity.subjects.Elective.practical
    at org.hibernate.engine.internal.Nullability.checkNullability(Nullability.java:92)
    at org.hibernate.action.internal.AbstractEntityInsertAction.nullifyTransientReferencesIfNotAlready(AbstractEntityInsertAction.java:115)
    at org.hibernate.action.internal.AbstractEntityInsertAction.makeEntityManaged(AbstractEntityInsertAction.java:124)
    at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:185)
    at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:163)
    at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:150)
    at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:325)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:272)
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:178)
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
    at org.hibernate.jpa.event.internal.core.JpaMergeEventListener.saveWithGeneratedId(JpaMergeEventListener.java:56)
    at org.hibernate.event.internal.DefaultMergeEventListener.saveTransientEntity(DefaultMergeEventListener.java:255)
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsTransient(DefaultMergeEventListener.java:235)
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:173)
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:69)
    at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:839)
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:821)
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:826)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:1161)
    ... 3 more

我做错了什么？这是hibernate中的一个错误吗？

Answer 1

optional=true元素仅用于生成DDL以及模式验证。如果您手动创建了数据库，那么即使您的Hibernate映射表明相反，实际的数据库列也可能是NOT NULL。

顺便说一下，你的映射可以缩小，例如我觉得你不需要targetEntity更新版本的Hibernate。

更新

我发现您在mappedBy - 元素的同一侧使用optional=true。 mappedBy - 元素告诉Hibernate关系的另一面包含实际的映射。它可能包含optional=true - 元素，因此会被忽略。尝试将其添加到关系的另一端。

JPA - optional = true仍然提供PropertyValueException

1 个答案: