Question

我有一个有2个不同List的课程。每个List使用不同的类作为它的泛型类型。这些类共享相同的基类。当我尝试持久化包含两个列表的类时，我得到一个错误，解释每个子类中不存在@Eelement注释中指定的列。但是此列存在于父类中。那么我怎么能告诉datanucleus这个列是在父类而不是子类中呢？

基类：

@PersistenceCapable(table = "Z")
@Inheritance(strategy = InheritanceStrategy.NEW_TABLE)
public abstract class Z {
    @Persistent(primaryKey = "true", valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Long id;

儿童班

@PersistenceCapable(table = "X")
@Inheritance(strategy = InheritanceStrategy.NEW_TABLE)
public class X extends Z {

@PersistenceCapable(table = "Y")
@Inheritance(strategy = InheritanceStrategy.NEW_TABLE)
public class Y extends Z {

我正试图坚持的课程：

@PersistenceCapable(table = "MyClass")
public class MyClass {
    @Persistent(column = "id", primaryKey = "true", valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Long id;
    // Specifies the FK column pointing to this object (ie. MyClass)
    @Element(column = "myclass_id")
    @Order(extensions = @Extension(vendorName = "datanucleus", key = "list-ordering", value = "order ASC"))
    private List<X> xList;

    // Specifies the FK column pointing to this object (ie. MyClass)
    @Element(column = "myclass_id")
    @Order(extensions = @Extension(vendorName = "datanucleus", key = "list-ordering", value = "order ASC"))
    private List<Y> yList;

这是我尝试持久MyClass时获得的堆栈跟踪的一部分。对于两个子类表，整个堆栈跟踪不止一次地重复相同的信息，所以我刚才提到了stackstrace的一部分：

Required columns missing from table "ipk.x" : myclass_id. Perhaps your MetaData is incorrect, or you havent enabled "datanucleus.schema.autoCreateColumns".
org.datanucleus.store.rdbms.exceptions.MissingColumnException: Required columns missing from table "ipk.x" : myclass_id. Perhaps your MetaData is incorrect, or you havent enabled "datanucleus.schema.autoCreateColumns".
    at org.datanucleus.store.rdbms.table.TableImpl.validateColumns(TableImpl.java:277)
    at org.datanucleus.store.rdbms.RDBMSStoreManager$ClassAdder.performTablesValidation(RDBMSStoreManager.java:3421)
    at org.datanucleus.store.rdbms.RDBMSStoreManager$ClassAdder.addClassTablesAndValidate(RDBMSStoreManager.java:3218)
    at org.datanucleus.store.rdbms.RDBMSStoreManager$ClassAdder.run(RDBMSStoreManager.java:2871)
    at org.datanucleus.store.rdbms.AbstractSchemaTransaction.execute(AbstractSchemaTransaction.java:119)
    at org.datanucleus.store.rdbms.RDBMSStoreManager.manageClasses(RDBMSStoreManager.java:1608)
    at org.datanucleus.store.rdbms.RDBMSStoreManager.getDatastoreClass(RDBMSStoreManager.java:678)
    at org.datanucleus.store.rdbms.RDBMSPersistenceHandler.getDatastoreClass(RDBMSPersistenceHandler.java:88)
    at org.datanucleus.store.rdbms.RDBMSPersistenceHandler.insertObject(RDBMSPersistenceHandler.java:123)
    at org.datanucleus.state.StateManagerImpl.internalMakePersistent(StateManagerImpl.java:3489)
    at org.datanucleus.state.StateManagerImpl.makePersistent(StateManagerImpl.java:3465)
    at org.datanucleus.ExecutionContextImpl.persistObjectInternal(ExecutionContextImpl.java:2031)
    at org.datanucleus.ExecutionContextImpl.persistObjectWork(ExecutionContextImpl.java:1874)
    at org.datanucleus.ExecutionContextImpl.persistObject(ExecutionContextImpl.java:1722)
    at org.datanucleus.api.jdo.JDOPersistenceManager.jdoMakePersistent(JDOPersistenceManager.java:722)
    at org.datanucleus.api.jdo.JDOPersistenceManager.makePersistent(JDOPersistenceManager.java:747)
    at ...

Answer 1

那么Z中的"myClass"字段是做什么的？也许它应该是 BI - 方向关系的一部分？在这种情况下，应该在所有者方（List（s））指定 mappedBy 。作为双向关系的一部分是您可以在Z中使用该列来存储List关系的FK的唯一方法。

Z中也没有“order”字段（指定为List（s）的一部分），因此该部分也不起作用。

如何在父类中使用@Element注释列时映射子类列表？

1 个答案: