CREATE TABLE Documents
(
  id INTEGER NOT NULL,discriminator ENUM('official','individual','external') NOT NULL,file_name VARCHAR(200) NOT NULL,PRIMARY KEY (id)
);

CREATE SystemDocuments
(
  id INTEGER NOT NULL,binary_data BLOB NOT NULL,PRIMARY KEY (id),FOREIGN KEY (id) REFERENCES Documents (id)
);

CREATE ExternalDocuments
(
  id INTEGER NOT NULL,FOREIGN KEY (id) REFERENCES SystemDocuments (id)
);

您可以看到所有的子表都是从Documents表中共享相同的ID.除此之外,SystemDocuments添加了一个binary_data列,而ExternalDocuments不添加新的属性. (还要注意,层次结构中还有两个其他具体的子表,由’official’和’individual’表示,这在这里是无关的.

以下是上表的映射：

Document.java：

@Entity
@Table(name = "Documents")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(name = "discriminator",discriminatorType = DiscriminatorType.STRING)
//@DiscriminatorOptions(force = true) // <-- Hibernate 4-specific annotation not inserting discriminator values
public abstract class Document implements Serializable
{
    @Id
    @Column
    protected Integer id;

    @Column(name = "file_name")
    protected String fileName;

    ...
}

SystemDocument.java：

@Entity
@Table(name = "SystemDocuments")
public abstract class SystemDocument extends Document
{
    @Lob
    @Column(name = "binary_data")
    protected byte[] binaryData;

    ...
}

ExternalDocument.java：

@Entity
@Table(name = "ExternalDocuments")
@DiscriminatorValue(value = "external")
public class ExternalDocument extends SystemDocument
{
    ...
}

后一类应被映射到文档的标识符列值“外部”.当通过EntityManager发现实体时,识别符被正确地返回,实际上是因为我的测试数据的识别符被正确插入数据块.

现在我使用以下代码通过JPA和文件上传器将新的文档/文件插入到系统中：

...

UploadedFile uf = event.getUploadedFile();

// set ID,file name,and binary data
ExternalDocument detachedExternalDocument =
    new ExternalDocument(1234567,uf.getName(),uf.getData());

docService.create(detachedExternalDocument);

当检查数据库时,我可以看到,Hibernate不会将“外部”鉴别器值插入到“文档”表的标识符列中.

过去有一些问题,见https://hibernate.onjira.com/browse/ANN-140,最近有关于Hibernate 4 https://hibernate.onjira.com/browse/HHH-4358的问题,所以很有可能这样工作.

然后我在当前的Hibernate 4 API文档中找到了http://docs.jboss.org/hibernate/core/4.0/javadocs/org/hibernate/annotations/DiscriminatorOptions.html,但它不起作用(参见Document Class中的@DiscriminatorOptions).

如何让Hibernate 4使用原始注释插入标识符？

注意：我不想将discriminator列映射为常规列.