JPA映射基本的類繼承

Question

我有JPA映射一個簡單的類：

@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; 
.... 

我已經延長該類成一個非常簡單的類

@Entity 
public class SponsorMaintainableBo extends Sponsor { 
} 

這正是我需要的SponsorMaintainableBo 。它是贊助商的副本，並且與贊助商從同一張表中讀取。這是我們的查詢框架所需要的，它是通過一些xml文檔控制的，並且需要成爲我正在做的一個單獨的對象。我們需要SponsorMaintainableBo來插入查詢/維護框架，以獲取我們不希望在主父文檔中定製的詳細信息。當我嘗試使用SponsorMaintainableBo，我得到以下錯誤：

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) 

我不知道映射子類，並繼承所有的JPA映射的最佳途徑。請指教。

Answer 1

Here約爲JPA實體繼承的一些信息。

你必須在你的實體配置的繼承，這是不夠的只是進行擴展的類。如果你想在一個單獨的表中有SponsorMaintainableBo，那麼用@Inheritance(strategy=TABLE_PER_CLASS)註釋Sponsor實體。在線有很多示例用於配置不同類型的繼承。

public enum InheritanceType { 
    SINGLE_TABLE, 
    JOINED, 
    TABLE_PER_CLASS 
}; 

Unknown column 'DTYPE' in 'field list'意味着SINGLE_TABLE是默認的繼承類型，並且您的JPA提供商正在尋找（默認命名）在目標表列DTYPE，以確定該實體的確切類型。

Answer 2

您還沒有指定的你有SponsorMaintainableBo所以其難度怎麼明白你在那裏的細節。

你沒有完全擴展以正確的方式你的實體。你需要給提示你將如何擴展原始數據庫中的表（一切都在同一個表束身，被稱爲SINGLE_TABLE？用一到一個參考的新表稱爲JOINED？表與副本新的字段被稱爲TABLE_PER_CLASS？）

您應該看看http://en.wikibooks.org/wiki/Java_Persistence/Inheritance以瞭解如何正確執行此操作。

UPDATE

雖然它仍然不是很清楚什麼SponsorMaintainableBO實際上是幹什麼的，從你加入我懷疑的原因是，你在這裏使用了錯誤的設計模式的細節。如果擴展JPA實體Bean，系統會希望你這樣做來添加額外的字段，因此它還添加了區分數據庫中兩個實體（超類和子類）的機制。默認情況下，如@Predrag所示，它需要一個名爲DTYPE的字段到表中，以便可以確定行是否是超類或子類的實例（繼承不是標準SQL所支持的）。還有其他可供使用的機制，例如完全獨立的表，或者通過外鍵將第2表連接在一起的第2表，僅添加由子類添加的字段。

從你所說的話

現在，你似乎並沒有做（或需要）的任何現象。如果我的理解正確，你將重載Entity bean的責任，並期望你的框架具有進一步的行爲。 Entity Beans被設計爲Beans，即數據的載體。如果您對它們進行了擴展，那麼JPA會明白，您正在這樣做是出於某種原因，添加更多數據（即更多字段）。你似乎想要的是你的實體的包裝，以便它也可以插入到你的框架中。這種方式兩個問題都保持分開，但仍然捆綁在一起。

我不知道你的框架期望從SponsorMaintainableBo期待什麼，但我的傾向是你應該使用不同的方法。而不是讓SponsorMaintainableBo延長Sponsor你或許應該把的Sponsor內SponsorMaintainableBo從而改變從SponsorMaintainableBo-is-A-Sponsor到SponsorMaintainableBo都具有一個-A-Sponsor的關係的實例。你可以做Sponsor構造函數的參數和不可變的這樣，如果你想這兩種情況下，以絕對耦合：如果上面是不夠的

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 
} 

，並且框架預計SponsorMaintainableBo一些領域都已普及與Sponsor你應該使用Decorator pattern。我相信你已經在SponsorContract有這個所以最有可能你需要做的是：

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 
} 

通過SponsorContract所需的方法只是委託函數調用底層Sponsor實例。 （請注意，完整的裝飾模式旨在將多個實例鏈接在一起，因此它會將SponsorContract sponsor而不是Sponsor sponsor添加到您的SponsorMaintainableBo，這樣您甚至可以將其他行爲鏈接到您的實體周圍，但我認爲您不需要這種複雜程度）