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几乎一整天，我都面临着一个涉及 JPA/Eclipselink 和 MySql 的问题。在我的 MySQL 数据库中，我通过以下方式配置了两个表：

Table: Member

memberID int(11) PK AI
desiresID int(11)
email
firstName
lastName
password

Table: MemberDesire

desireID int(11) PK AI

with ForeignKey constraint between Member and MemberDesire
using Member.desireID and MemberDesire.desireID

在 Eclipse 中，我让这些表自动导入，它可以完美地识别链接。这两个类如下所示：

    @Entity
    public class Member implements Serializable {
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int memberID;

private String email;

private String firstName;

private String lastName;

private String password;

//bi-directional many-to-one association to MemberDesire
@ManyToOne(cascade=CascadeType.PERSIST)
@JoinColumn(name="desiresID")
private MemberDesire memberDesire;

和：

    @Entity
    @Table(name="MemberDesires")
    public class MemberDesire implements Serializable {
private static final long serialVersionUID = 1L;

@Id
private int desireID;

private int maximumAge;

private int minimumAge;

//bi-directional many-to-one association to Member
@OneToMany(mappedBy="memberDesire")
private List<Member> members;

现在，当我尝试将包含 MemberDesire 的新成员持久保存到数据库时，会出现以下错误：

Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`test`.`member`, CONSTRAINT `desireKey` FOREIGN KEY (`desiresID`) REFERENCES `MemberDesires` (`desireID`) ON DELETE NO ACTION ON UPDATE NO ACTION)
Error Code: 1452
Call: INSERT INTO MEMBER (EMAIL, FIRSTNAME, LASTNAME, PASSWORD, desiresID) VALUES (?, ?, ?, ?, ?,)
    bind => [5 parameters bound]

持久化本身是通过这种方式完成的：

EntityManager em = Persistence

                .createEntityManagerFactory("TestProject")
                .createEntityManager();
        EntityTransaction entityTransaction = em.getTransaction();

        entityTransaction.begin();

        member = new Member();
        member.setFirstName(firstName);
        member.setLastName(lastName);
        member.setEmail(email);
        member.setPassword(password);

        MemberDesire desire = new MemberDesire();
        member.setMemberDesire(desire);

        List<Member> members = new ArrayList<Member>();
        members.add(member);
        desire.setMembers(members);

        em.persist(member);

        entityTransaction.commit();

        em.close();

我将非常感谢您能给我的任何帮助！！谢谢 ：）

塞巴斯蒂安

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1 回答 1

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MemberDesire 未设置为生成主键，因此当您调用

 MemberDesire desire = new MemberDesire();
 member.setMemberDesire(desire);

it should result in an invalid MemberDesire entity with a null pk being associated to the member. You can turn EclipseLink logging level to Finest to see the SQL and the parameters that are issued which might help prove the problem. If you are trying to associate an existing MemberDesire to a new Member, you should use the em.find() api or query for the entity so that you can associate the managed instance instead of creating a new object.

于 2012-08-31T15:16:12.920 回答