java - 使用继承的 JPA OneToMany

Question

我有以下类(class):

硬件.java

    @Entity
    @Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
    public class Hardware{
    @Id
    @GeneratedValue(strategy=GenerationType.TABLE)
    private long id;
    private String serialnumber;    

    @OneToMany (mappedBy="hardware")
    private List<Equipment> equipments;
}

计算机.java

    @Entity
    public class Computer extends Hardware {

    private String hostname;
    private String macAdress;
    private String ipNumber;

    public Computer(){
        super();
    }

    public Computer(String serialnumber, String hostname,
        String macAdress, String ipNumber) {
        super(serialnumber);
        this.hostname = hostname;
        this.macAdress = macAdress;
        this.ipNumber = ipNumber;
    }
}

NetworkDeivce.java

    @Entity
    public class NetworkDevice extends Hardware {

    private String hostname;
    private String ipAdress;

    public NetworkDevice(){
        super();
    }

    public NetworkDevice(String serialnumber, String hostname,
            String ipAdress) {
        super(serialnumber);
        this.hostname = hostname;
        this.ipAdress = ipAdress;
    }
}

现在映射到硬件类的类:

设备.java

@Entity
public class Equipment {

    public Equipment(){
    }
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private long id;
    private String serialnumber;
    private String info;

    @ManyToOne (fetch=FetchType.EAGER)
    @JoinColumn(name="HW_ID")
    private Hardware hardware;
}

现在，如果我将设备添加到计算机，一切都会正常工作，但如果我尝试将设备添加到网络设备，则会收到此错误:内部异常:

内部异常:

com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`inventorytool_beta`.`EQUIPMENT`, CONSTRAINT `FK_EQUIPMENT_HW_ID` FOREIGN KEY (`HW_ID`) REFERENCES `COMPUTER` (`ID`))
Error Code: 1452
Call: INSERT INTO EQUIPMENT (INFO, SERIALNUMBER, HW_ID) VALUES (?, ?, ?)
    bind => [3 parameters bound]
Query: InsertObjectQuery(domain.hardware.Equipment@600a620d)
    at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commitInternal(EntityTransactionImpl.java:102)
    at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commit(EntityTransactionImpl.java:63)
    at main.dbTest(main.java:74)
    at main.main(main.java:18)
Caused by: Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.4.1.v20121003-ad44345): 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 (`inventorytool_beta`.`EQUIPMENT`, CONSTRAINT `FK_EQUIPMENT_HW_ID` FOREIGN KEY (`HW_ID`) REFERENCES `COMPUTER` (`ID`))
Error Code: 1452
Call: INSERT INTO EQUIPMENT (INFO, SERIALNUMBER, HW_ID) VALUES (?, ?, ?)
    bind => [3 parameters bound]
Query: InsertObjectQuery(domain.hardware.Equipment@600a620d)
    at org.eclipse.persistence.exceptions.DatabaseException.sqlException(DatabaseException.java:324)
    at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeDirectNoSelect(DatabaseAccessor.java:851)
    at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeNoSelect(DatabaseAccessor.java:913)
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`inventorytool_beta`.`EQUIPMENT`, CONSTRAINT `FK_EQUIPMENT_HW_ID` FOREIGN KEY (`HW_ID`) REFERENCES `COMPUTER` (`ID`))
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)

所以我认为这是继承的问题...我不太擅长JPA..

提前致谢。

Answer 1

查看生成的架构。由于您的继承策略，您应该拥有三个不同的硬件表:一张用于 Hardware，一张用于 Computer，一张用于 NetworkDevice。问题是 HW_ID 只能引用一张表。在这里，您的 JPA 提供程序选择了 Computer，可能是因为它按字母顺序排列在第一个，但它无法处理所有三个类。

考虑使用另一种继承策略，例如JOIN。