Question

我有一个这样的模型：

@Validated
@Entity(name = "A")
@XmlRootElement(name = "A")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({B.class})
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
@UuidGenerator(name="a_key_guid")
@Cacheable(false)
public abstract class A{

}

@Entity
@Table(name = "b")
@XmlType(name = "b")
public class B extends A {

}

A类不应该有表。为简单起见，省略了列。

如果我尝试执行一个简单的查询，例如：

 SELECT COUNT(*) FROM A

我收到以下错误，我尝试搜索但我找不到任何具体的答案。为什么不从具体课程中取出？我尝试使用@MappedSuperClass但结果是一样的。

            Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Table 'a' doesn't exist
    Error Code: 1146
    Call: SELECT COUNT(*) FROM A
        bind => [1 parameter bound]
    Query: ReportQuery(referenceClass=A sql="SELECT COUNT(*) FROM A")
        at org.eclipse.persistence.exceptions.DatabaseException.sqlException(DatabaseException.java:340)
        at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.basicExecuteCall(DatabaseAccessor.java:682)
        at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeCall(DatabaseAccessor.java:558)
        at org.eclipse.persistence.internal.sessions.AbstractSession.basicExecuteCall(AbstractSession.java:1991)
        at org.eclipse.persistence.sessions.server.ClientSession.executeCall(ClientSession.java:298)
        at org.eclipse.persistence.internal.queries.DatasourceCallQueryMechanism.executeCall(DatasourceCallQueryMechanism.java:242)
        at org.eclipse.persistence.internal.queries.DatasourceCallQueryMechanism.executeCall(DatasourceCallQueryMechanism.java:228)
        at org.eclipse.persistence.internal.queries.DatasourceCallQueryMechanism.executeSelectCall(DatasourceCallQueryMechanism.java:299)
        at org.eclipse.persistence.internal.queries.DatasourceCallQueryMechanism.selectAllRows(DatasourceCallQueryMechanism.java:694)
        at org.eclipse.persistence.internal.queries.ExpressionQueryMechanism.selectAllRowsFromTable(ExpressionQueryMechanism.java:2738)
        at org.eclipse.persistence.internal.queries.ExpressionQueryMechanism.selectAllReportQueryRows(ExpressionQueryMechanism.java:2675)
        at org.eclipse.persistence.queries.ReportQuery.executeDatabaseQuery(ReportQuery.java:848)
        at org.eclipse.persistence.queries.DatabaseQuery.execute(DatabaseQuery.java:899)
        at org.eclipse.persistence.queries.ObjectLevelReadQuery.execute(ObjectLevelReadQuery.java:1127)
        at org.eclipse.persistence.queries.ReadAllQuery.execute(ReadAllQuery.java:403)
        at org.eclipse.persistence.queries.ObjectLevelReadQuery.executeInUnitOfWork(ObjectLevelReadQuery.java:1215)
        at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.internalExecuteQuery(UnitOfWorkImpl.java:2896)
        at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1793)
        at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1775)
        at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1740)
        at org.eclipse.persistence.internal.jpa.QueryImpl.executeReadQuery(QueryImpl.java:258)
        ... 116 more
    Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Table 'a' doesn't exist
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
        at com.mysql.jdbc.Util.getInstance(Util.java:386)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1054)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4120)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4052)
        at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2503)
        at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2664)
        at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2815)
        at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2155)
        at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2322)
        at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeSelect(DatabaseAccessor.java:1007)
        at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.basicExecuteCall(DatabaseAccessor.java:642)
        ... 135 more

如果我确实创建了B对象并将其保留，则模型会正确更新。

EclipseLink的版本是2.5.1

Answer 1

这是您要发出的本机SQL查询：您的数据库如何知道有关您的类层次结构的任何信息？无论如何，如果A没有表，它不是实体，应该是MappedSuperclass：

http://en.wikibooks.org/wiki/Java_Persistence/Inheritance#Mapped_Superclasses

映射的超类继承允许在继承中使用继承对象模型，当它在数据模型中不存在时。

但请注意，您无法跨MappedSuperclass定义的类层次结构进行查询。

EclipseLink TABLE_PER_CLASS继承：查询尝试从超类而不是具体类中获取

1 个答案: