Java EE 6 JPA 2 ManyToOne Relation创建无效的外键

Question

我正在尝试创建两个实体,其中两个实体都有embeddedIds.其中一个实体有2个引用另一个实体,其中这两个引用都与ManyToOne相关.

示例代码如下:

@Embeddable
public class ItemPK {
  @Column(nullable = false, length = 100)
  private String itemId;
  @Column(name = "item_client_id", nullable = false)
  private int clientId; 
  ...
}

@Entity
@Table(name = "item")
public class Item {
  @EmbeddedId
  private ItemPK id;

  @ManyToOne
  @JoinColumn(name = "item_client_id")
  private Client client;

  @OneToMany(mappedBy="item", cascade = CascadeType.ALL, orphanRemoval = true)
  private Set<RelatedItem> relatedItems;

  @OneToMany(mappedBy="relatedItem", cascade = CascadeType.ALL, orphanRemoval = true)
  private Set<RelatedItem> relatedItemsRHS;
  ...
}

@Embeddable
public class RelatedItemPK {
  @Column(name = "itemId", length = 100, nullable = false)
  private String itemId;
  @Column(name = "item_client_id", nullable = false)
  private int clientId;
  @Column(name = "relatedItemId", length = 100, nullable = false)
  private String relatedItemId;
  @Column(name = "related_item_client_id", nullable = false)
  private int relatedItemClientId;
  ...
}

@Entity
@Table(name = "related_item")
public class RelatedItem {
  @EmbeddedId
  private RelatedItemPK id;

  @ManyToOne(cascade = CascadeType.ALL, optional = false)
  @JoinColumns({
    @JoinColumn(name="itemId", referencedColumnName="itemId", insertable=false, updatable=false),
    @JoinColumn(name="item_client_id", referencedColumnName="item_client_id", insertable=false, updatable=false)
  })
  private Item item;
  @ManyToOne(cascade = CascadeType.ALL, optional = false)
  @JoinColumns({
    @JoinColumn(name="related_item_client_id", referencedColumnName="item_client_id", insertable=false, updatable=false),
    @JoinColumn(name="relatedItemId", referencedColumnName="itemId", insertable=false, updatable=false)
  })
  private Item relatedItem;
  ...
}

问题是在为RelatedItem实体创建外键时,我得到了一个SQLException.这是第二个失败的ManyToOne关系.外键生成sql如下,

ALTER TABLE related_item ADD CONSTRAINT FK_related_item_related_item_client_id FOREIGN KEY (related_item_client_id, relatedItemId) REFERENCES item (item_client_id, itemId)

由于item表首先由itemId索引,然后由item_client_id索引,因此该语句会导致MySQL产生错误.

我想切换列的位置,以便SQL应如下所示,

ALTER TABLE related_item ADD CONSTRAINT FK_related_item_relatedItemId FOREIGN KEY (relatedItemId, related_item_client_id) REFERENCES item (itemId,item_client_id)

我尝试更改"JoinColumn"的顺序,但结果没有改变.我还尝试重命名字段以检查持久性提供程序是否按列名选择顺序,但结果再次没有更改.

那么,有没有办法强制执行列排序？

ps我使用以下内容:

• MySQL 5.1
• EclipseLink 2.0.0
• Java EE 6
• JPA 2
• GlassFish v3

编辑:EclipseLink生成以下SQL,无法运行;

CREATE TABLE related_item (SIMILARITY DOUBLE, widget_id INTEGER NOT NULL, relatedItemId VARCHAR(100) NOT NULL, itemId VARCHAR(100) NOT NULL, related_item_client_id INTEGER NOT NULL, item_client_id INTEGER NOT NULL, PRIMARY KEY (widget_id, relatedItemId, itemId, related_item_client_id, item_client_id));
CREATE TABLE item (IMAGEURL VARCHAR(2048), STATUS VARCHAR(64), URL VARCHAR(2048), PRICE DOUBLE, STOCK INTEGER, DESCRIPTION TEXT(64000), NAME VARCHAR(255), ITEMID VARCHAR(100) NOT NULL, item_client_id INTEGER NOT NULL, PRIMARY KEY (ITEMID, item_client_id));
ALTER TABLE related_item ADD CONSTRAINT FK_related_item_itemId FOREIGN KEY (itemId, item_client_id) REFERENCES item (itemId, item_client_id);
ALTER TABLE related_item ADD CONSTRAINT FK_related_item_related_item_client_id FOREIGN KEY (related_item_client_id, relatedItemId) REFERENCES item (item_client_id, itemId);
ALTER TABLE item ADD CONSTRAINT FK_item_item_client_id FOREIGN KEY (item_client_id) REFERENCES client (ID);

Answer 1

请包含堆栈跟踪。但是，我强烈建议您跳过 @JoinColumn 标记，除非您有充分的理由自己指定外键。通过在其中一个方向上指定mappedBy属性，JPA可以弄清楚自己要做什么。

Java EE 6 和 JPA 投入了大量精力来启用约定优于配置，这意味着大多数时候，一切都可以开箱即用。这对于程序员来说是理想的，因为您无需担心样板代码，对于 JPA 和 Jave EE 容器实现者来说也是理想的，因为这使他们可以自由地选择性能最佳的解决方案。通过自己声明外键关系，您和 JPA 都失去了这一优势。

编辑：事实上，我怀疑指定mappedBy 和指定@JoinTable 可能是问题的根本原因。但我需要查看堆栈跟踪才能确定。