为什么我持久存在“外键约束失败”异常？

Question

美好的一天，请告知我为什么会遇到异常情况。我是EclipseLink初学者，我使用的是jdk1.7.0_05，MySQL服务器5.5.25a。

Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`stats`.`version`, CONSTRAINT `fk_version_activity1` FOREIGN KEY (`activity_id`, `activity_license_id`) REFERENCES `activity` (`id`, `license_id`) ON DELETE NO ACTION ON UPDATE NO ACTION)
Error Code: 1452
Caused by: javax.persistence.PersistenceException: Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.3.0.v20110604-r9504): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`stats`.`version`, CONSTRAINT `fk_version_activity1` FOREIGN KEY (`activity_id`, `activity_license_id`) REFERENCES `activity` (`id`, `license_id`) ON DELETE NO ACTION ON UPDATE NO ACTION)
Error Code: 1452
Call: INSERT INTO version (version, activity_id, product, activity_license_id) VALUES (?, ?, ?, ?)
bind => [4 parameters bound]
Query: InsertObjectQuery(cz.ryvo.stats.database.Version[ versionPK=cz.ryvo.stats.database.VersionPK[ product=AP, activityId=0, activityLicenseId=0 ] ])
at org.eclipse.persistence.internal.jpa.EntityManagerImpl.flush(EntityManagerImpl.java:786)
at cz.audatex.audaupdateloader.DatabaseHelper.registerActivity(DatabaseHelper.java:104)
... 3 more

表格许可证如下所示：

CREATE TABLE `license` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `license` varchar(20) NOT NULL,
  `organisation_id` int(11) DEFAULT NULL,
  `user_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `license_UNIQUE` (`license`),
  KEY `fk_license_user1` (`user_id`),
  KEY `fk_license_organisation1` (`organisation_id`),
  CONSTRAINT `fk_license_organisation1` FOREIGN KEY (`organisation_id`) REFERENCES `organisation` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  CONSTRAINT `fk_license_user1` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=latin1;

表活动：

CREATE TABLE `activity` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `license_id` int(11) NOT NULL,
  `time` datetime NOT NULL,
  `type` char(1) NOT NULL,
  `result` int(1) DEFAULT NULL,
  PRIMARY KEY (`id`,`license_id`),
  UNIQUE KEY `activity_UQ01` (`license_id`,`time`,`type`),
  KEY `fk_activity_license1` (`license_id`),
  CONSTRAINT `fk_activity_license1` FOREIGN KEY (`license_id`) REFERENCES `license` (`id`) ON DELETE CASCADE ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=latin1;

表格版本：

CREATE TABLE `version` (
  `product` varchar(45) NOT NULL,
  `activity_id` int(11) NOT NULL,
  `activity_license_id` int(11) NOT NULL,
  `version` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`product`,`activity_id`,`activity_license_id`),
  KEY `fk_version_activity1` (`activity_id`,`activity_license_id`),
  CONSTRAINT `fk_version_activity1` FOREIGN KEY (`activity_id`, `activity_license_id`) REFERENCES `activity` (`id`, `license_id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

我在NetBeans中使用New-＆gt;数据库中的实体类生成的类看起来像这样：

班级版本：

@Entity
@Table(name = "version")
@XmlRootElement
public class Version implements Serializable {
    private static final long serialVersionUID = 1L;
    @EmbeddedId
    protected VersionPK versionPK;
    @Column(name = "version")
    private String version;
    @JoinColumns({
        @JoinColumn(name = "activity_id", referencedColumnName = "id", insertable = false, updatable = false),
        @JoinColumn(name = "activity_license_id", referencedColumnName = "license_id", insertable = false, updatable = false)})
    @ManyToOne(optional = false, fetch = FetchType.LAZY)
    private Activity activity;
    ...

Class VersionPK：

@Embeddable
public class VersionPK implements Serializable {
    @Basic(optional = false)
    @Column(name = "product")
    private String product;
    @Basic(optional = false)
    @Column(name = "activity_id")
    private int activityId;
    @Basic(optional = false)
    @Column(name = "activity_license_id")
    private int activityLicenseId;
    ...

我在执行以下代码时遇到异常：

...
ActivityPK apk = new ActivityPK();
apk.setLicenseId(activity.getLicense().getId());
activity.setActivityPK(apk);
em.persist(activity);
em.flush(); <- Here the exception is thrown
...

我怀疑是因为活动尚未分配ID而VerionPK使用此ID。我对吗？保留此类数据的正确方法是什么？在将版本集合设置为null的持久化活动后，我是否应该单独保留版本集合？ 提前谢谢了。 Vojtech

Answer 1

查看JPA 2.0的派生ID。您可以将关系标记为ID，或者使用映射Id指定id字段的关系，而不必自己手动设置值。这会在创建新树时处理问题，并且根实体使用顺序 - 在持久保存根之前，子项无法使用id作为外键。

否则，需要持久保存和刷新根实体，以便分配Id。在这种情况下，Activity实体需要主键值才能尝试并保留引用它的新Version对象，因为您必须手动设置所有version.versionpk值。