具有基本类继承的JPA映射

Question

我有一个用JPA映射的简单类：

@Entity
@Table(name = "SPONSOR")
public class Sponsor extends PersistableBusinessObjectBase implements SponsorContract {

@PortableSequenceGenerator(name = "SEQ_SPONSOR_CODE")
@GeneratedValue(generator = "SEQ_SPONSOR_CODE")
@Id
@Column(name = "SPONSOR_CODE")
private String sponsorCode;

@Column(name = "ACRONYM")
private String acronym;

@Column(name = "AUDIT_REPORT_SENT_FOR_FY")
private String auditReportSentForFy;

@Column(name = "CAGE_NUMBER")
private String cageNumber;

@Column(name = "COUNTRY_CODE")
private String countryCode;

@Column(name = "DODAC_NUMBER")
private String dodacNumber;

@Column(name = "DUN_AND_BRADSTREET_NUMBER")
private String dunAndBradstreetNumber;

@Column(name = "DUNS_PLUS_FOUR_NUMBER")
private String dunsPlusFourNumber;

@Column(name = "OWNED_BY_UNIT")
private String ownedByUnit;

@Column(name = "POSTAL_CODE")
private String postalCode;

@Column(name = "ROLODEX_ID")
private Integer rolodexId;

@Column(name = "SPONSOR_NAME")
private String sponsorName;

@Column(name = "SPONSOR_TYPE_CODE")
private String sponsorTypeCode;

@Column(name = "STATE")
private String state;

@Column(name = "CREATE_USER")
private String createUser;

@Column(name = "ACTV_IND")
@Convert(converter = BooleanYNConverter.class)
private boolean active;

@ManyToOne(cascade = { CascadeType.REFRESH })
@JoinColumn(name = "SPONSOR_TYPE_CODE", referencedColumnName = "SPONSOR_TYPE_CODE", insertable = false, updatable = false)
private SponsorType sponsorType;

@ManyToOne(cascade = { CascadeType.REFRESH })
@JoinColumn(name = "OWNED_BY_UNIT", referencedColumnName = "UNIT_NUMBER", insertable = false, updatable = false)
private Unit unit;

@ManyToOne(cascade = { CascadeType.REFRESH })
@JoinColumn(name = "ROLODEX_ID", referencedColumnName = "ROLODEX_ID", insertable = false, updatable = false)
private Rolodex rolodex;
....

我把那门课扩展成了非常简单的课

@Entity
public class SponsorMaintainableBo extends Sponsor {
}

这正是我对SponsorDefainableBo所需要的。它是Sponsor的副本，并且从与Sponsor相同的表中读取。这是我们通过一些xml文档控制的查询框架所需要的，并且需要成为我正在做的事情的单独对象。需要SponsorDefainableBo插入查询/维护框架以进行我们不想在主父文档中进行的自定义详细信息。当我尝试使用SponsorDefainableBo时，我得到以下错误：

org.springframework.orm.jpa.JpaSystemException: Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.MySQLSyntaxErrorException: Unknown column 'DTYPE' in 'field list'
Error Code: 1054
Call: SELECT SPONSOR_CODE AS a1, DTYPE AS a2, ACRONYM AS a3, ACTV_IND AS a4, AUDIT_REPORT_SENT_FOR_FY AS a5, CAGE_NUMBER AS a6, COUNTRY_CODE AS a7, CREATE_USER AS a8, DODAC_NUMBER AS a9, DUN_AND_BRADSTREET_NUMBER AS a10, DUNS_PLUS_FOUR_NUMBER AS a11, OBJ_ID AS a12, OWNED_BY_UNIT AS a13, POSTAL_CODE AS a14, ROLODEX_ID AS a15, SPONSOR_NAME AS a16, SPONSOR_TYPE_CODE AS a17, STATE AS a18, UPDATE_TIMESTAMP AS a19, UPDATE_USER AS a20, VER_NBR AS a21 FROM SPONSOR WHERE (DTYPE = ?) LIMIT ?, ?
bind => [3 parameters bound]
Query: ReadAllQuery(referenceClass=SponsorMaintainableBo sql="SELECT SPONSOR_CODE AS a1, DTYPE AS a2, ACRONYM AS a3, ACTV_IND AS a4, AUDIT_REPORT_SENT_FOR_FY AS a5, CAGE_NUMBER AS a6, COUNTRY_CODE AS a7, CREATE_USER AS a8, DODAC_NUMBER AS a9, DUN_AND_BRADSTREET_NUMBER AS a10, DUNS_PLUS_FOUR_NUMBER AS a11, OBJ_ID AS a12, OWNED_BY_UNIT AS a13, POSTAL_CODE AS a14, ROLODEX_ID AS a15, SPONSOR_NAME AS a16, SPONSOR_TYPE_CODE AS a17, STATE AS a18, UPDATE_TIMESTAMP AS a19, UPDATE_USER AS a20, VER_NBR AS a21 FROM SPONSOR WHERE (DTYPE = ?) LIMIT ?, ?"); nested exception is javax.persistence.PersistenceException: Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.MySQLSyntaxErrorException: Unknown column 'DTYPE' in 'field list'
Error Code: 1054
Call: SELECT SPONSOR_CODE AS a1, DTYPE AS a2, ACRONYM AS a3, ACTV_IND AS a4, AUDIT_REPORT_SENT_FOR_FY AS a5, CAGE_NUMBER AS a6, COUNTRY_CODE AS a7, CREATE_USER AS a8, DODAC_NUMBER AS a9, DUN_AND_BRADSTREET_NUMBER AS a10, DUNS_PLUS_FOUR_NUMBER AS a11, OBJ_ID AS a12, OWNED_BY_UNIT AS a13, POSTAL_CODE AS a14, ROLODEX_ID AS a15, SPONSOR_NAME AS a16, SPONSOR_TYPE_CODE AS a17, STATE AS a18, UPDATE_TIMESTAMP AS a19, UPDATE_USER AS a20, VER_NBR AS a21 FROM SPONSOR WHERE (DTYPE = ?) LIMIT ?, ?
bind => [3 parameters bound]
Query: ReadAllQuery(referenceClass=SponsorMaintainableBo sql="SELECT SPONSOR_CODE AS a1, DTYPE AS a2, ACRONYM AS a3, ACTV_IND AS a4, AUDIT_REPORT_SENT_FOR_FY AS a5, CAGE_NUMBER AS a6, COUNTRY_CODE AS a7, CREATE_USER AS a8, DODAC_NUMBER AS a9, DUN_AND_BRADSTREET_NUMBER AS a10, DUNS_PLUS_FOUR_NUMBER AS a11, OBJ_ID AS a12, OWNED_BY_UNIT AS a13, POSTAL_CODE AS a14, ROLODEX_ID AS a15, SPONSOR_NAME AS a16, SPONSOR_TYPE_CODE AS a17, STATE AS a18, UPDATE_TIMESTAMP AS a19, UPDATE_USER AS a20, VER_NBR AS a21 FROM SPONSOR WHERE (DTYPE = ?) LIMIT ?, ?")
at org.springframework.orm.jpa.EntityManagerFactoryUtils.convertJpaAccessExceptionIfPossible(EntityManagerFactoryUtils.java:321)
at org.springframework.orm.jpa.DefaultJpaDialect.translateExceptionIfPossible(DefaultJpaDialect.java:120)

我不确定映射子类和继承所有JPA映射的最佳方法。请建议。

Answer 1

您尚未指定您在ProundnerMaintainableBo中拥有的内容的详细信息，因此很难理解您在那里拥有的内容。

你还没有以正确的方式扩展你的实体。您需要给出如何扩展数据库中的原始表的提示(所有内容都集中在同一个表中，称为< code>SINGLE_TABLE？具有一对一引用的新表称为< code>JOINED？具有新字段的表的副本，称为< code>TABLE_PER_CLASS？)

您应该查看 http://en.wikibooks.org/wiki/Java_Persistence/Inheritance，以了解如何正确实现它。

更新

虽然目前还不太清楚ProunderMaintainableBO实际上在做什么，但从你添加的细节来看，我怀疑原因是你在这里使用了错误的设计模式。如果扩展 JPA 实体 Bean，系统将期望您这样做是为了添加其他字段，因此它还添加了区分数据库中两个实体（超类和子类）的机制。默认情况下，如 @Predrag 它期望表中有一个名为 DTYPE 的字段，以便可以标识行，无论它是超类的实例还是子类（继承不是标准 SQL 支持的内容）。您可以使用其他机制，例如完全独立的表，或者由外键连接在一起的 2 个表，第 2 个表仅添加子类添加的字段。

现在从你所说的，你似乎没有做（或需要）任何这些。如果我理解正确，你正在用你的框架预期的进一步行为来超载实体bean的责任。实体Bean被设计为只是Bean，即数据的载体。如果你扩展它们，JPA明白你这样做是有原因的，添加更多数据（即更多的字段）。你似乎想要的是实体的包装器，以便它也插入到你的框架中。这样，这两个问题就分开了，但仍然联系在一起。

我不知道你的框架对ProstrandMaintainableBo的期望是什么，但我的倾向是你应该使用不同的方法。与其让 SponsorMaintainableBo 扩展 Sponsor，不如将 Sponsor 的实例放在 SponsorMaintainableBo 中，从而将关系从 SponsorMaintainableBo -is-a- Sponsor 更改为 SponsorMaintainableBo -has-a- Sponsor。如果您希望两个实例都绝对耦合，则可以使 Sponsor 成为构造函数参数，并且如下所示不可变：

public class SponsorMaintainableBo 
{
   private final Sponsor sponsor;

   public SponsorMaintainableBo(Sponsor sponsor)
   {
      this.sponsor = sponsor;
   }

   public Sponsor getSponsor()
   {
      return this.sponsor;
   }

   //... rest of the methods expected by the framework
}

如果上述内容还不够，并且框架需要＜code＞赞助商可维护BO＜/code＞中的一些字段，这些字段与＜code＞赞助者＜/code＞相同，那么您应该使用Decorator模式。我想您在＜code＞赞助商合同＜/code＞中已经有了这个，所以您最可能需要做的是：

public class SponsorMaintainableBo implements SponsorContract
{
   private final Sponsor sponsor;

   public SponsorMaintainableBo(Sponsor sponsor)
   {
      this.sponsor = sponsor;
   }

   public Sponsor getSponsor()
   {
      return this.sponsor;
   }

   //... rest of the methods specified by `SponsorContract`

   //... rest of the methods expected by the framework
}

Sponsor合约所需的方法只是将函数调用委托给底层Sponsor实例。

（请注意，完整的装饰器模式旨在将多个实例链接在一起，因此它会将 SponsorContract sponsor 而不是 Sponsor Sponsor Sponsor 添加到您的 SponsorMaintainableBo 中，这样您甚至可以将其他行为链接在实体周围，但我认为您不需要这种复杂程度）

Answer 2

以下是关于JPA实体继承的一些信息。

您必须在实体上配置继承，仅仅扩展类是不够的。如果希望将＜code＞赞助商可维护BO＜/code＞放在一个单独的表中，则使用＜code＞继承（strategy=table_PER_CLASS）＜/code>注释＜code＞赞助＜/code＞实体。在线上有很多配置不同类型继承的示例。

public enum InheritanceType {
    SINGLE_TABLE,
    JOINED,
    TABLE_PER_CLASS
};

字段列表中的未知列'DTYPE'表示SINGLE_TABLE是默认继承类型，并且您的JPA提供程序正在目标表中查找（默认命名）列DTYPE，以确定实体的确切类型。