JPA/Hibernate——实体名称似乎很重要。如果我改名为"；“鲍勃”；很好

这个问题已经困扰了我好几个小时了。这与我的另一个问题有关：

我去掉了几乎所有的代码，缩小了问题的范围。我有三个非常简单的实体：

@Entity
public class Building {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    public Building() {
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }
}

Other.java

@Entity
public class Other {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "building_id")
    private Building building;

    public Other() {
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Building getBuilding() {
        return building;
    }

    public void setBuilding(Building school) {
        this.building = school;
    }
}

Event.java

@Entity
public class Event {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private long id;

    @ManyToOne
    @JoinColumn(name = "other_id")
    private Other other;


    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public Other getOther() {
        return other;
    }

    public void setOther(Other other) {
        this.other = other;
    }
}

这将因外键约束冲突而失败：

Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`blah`.`event`, CONSTRAINT `FK403827A76D0546B` FOREIGN KEY (`other_id`) REFERENCES `Other` (`id`))
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)

现在这里是真正奇怪的部分！！！！如果我进行eclipse重构并将“其他”实体重命名为“Bob”，那么它工作得非常好。正如我们在同一页上一样，事件实体现在将如下所示：

@Entity
public class Event {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private long id;

    @ManyToOne
    @JoinColumn(name = "bob_id")
    private Bob bob;


    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public Bob getBob() {
        return bob;
    }

    public void setBob(Bob bob) {
        this.bob = bob;
    }
}

现在它工作得非常好。有人能给我这样的冬眠新手解释一下吗？这真让我难堪。将新事件持久化到我的服务层中的数据库时失败：

@Transactional(propagation=Propagation.REQUIRED, rollbackFor=Exception.class) 
public void addEvent(Event event) throws ErrorCodeException, Exception
{
    // not sure if I need to do this, still fails if I remove it
    event.setOther(otherDAO.getReferenceById(event.getOther().getId()));
    eventDAO.persist(event);
}

还有一点意见。除了将Other重命名为Bob，我还可以将表名设置为小写：

@Entity
@Table(name = "other")
public class Other {

这也解决了这个问题。但我不能接受这些解决方案。我想知道为什么会失败。我做了一个技术决定，不使用Grails来避免这种“魔法”

以下是SQL hibernate日志：

// Initial database inserts
Hibernate: insert into Building values ( )
Hibernate: insert into Other (building_id) values (?)

// Insert which throws exception
Hibernate: insert into Event (other_id) values (?)
2011-06-27 11:31:51 JDBCExceptionReporter [WARN] SQL Error: 1452, SQLState: 23000
2011-06-27 11:31:51 JDBCExceptionReporter [ERROR] Cannot add or update a child row: a foreign key constraint fails (`blah`.`event`, CONSTRAINT `FK403827A76D0546B` FOREIGN KEY (`other_id`) REFERENCES `Other` (`id`))
org.springframework.orm.jpa.JpaSystemException: org.hibernate.exception.ConstraintViolationException: could not insert: [com.blah.server.domain.Event]; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: could not insert: [com.blah.server.domain.Event]

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更新：我在这里找到了解决方案：

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似乎mysql、hibernate和MacOSX的结合导致了这个问题。作为解决方案，使用小写命名策略。

哪个实体映射到表blah？我想知道hibernate是否正在生成一个以mysql关键字作为其中一列名称的查询。可以添加hibernate生成的查询吗？blah是数据库名称。我将查询添加到最初的帖子中。谢谢你的帮助！我在Mac OS席上运行MySQL 5.1找到了解决方案。似乎是MacOSX、hibernate和mysql的组合导致了这个问题。见：