hibernate映射合成模式的问题

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"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

polymorphism="explicit">



not-null="true" type="string" unique="true" />
type="timestamp" />
type="text" />

lazy="proxy" name="group" />





extends="xhlh.ac.Principal">






extends="xhlh.ac.Principal">

not-null="true" type="string" />
not-null="true" type="string" />
name="groupAdmin" type="boolean" />


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我用new SchemaExport(config).create(true, true);导出表时抛出异常：
Exception in thread "main" org.hibernate.MappingException: An association from the table principal refers to an unmapped class: GroupModel
at org.hibernate.cfg.Configuration.secondPassCompileForeignKeys(Configuration.java:1252)
at org.hibernate.cfg.Configuration.secondPassCompileForeignKeys(Configuration.java:1260)
at org.hibernate.cfg.Configuration.secondPassCompileForeignKeys(Configuration.java:1260)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1170)
at org.hibernate.cfg.Configuration.generateDropSchemaScript(Configuration.java:756)
at org.hibernate.tool.hbm2ddl.SchemaExport.(SchemaExport.java:93)
at org.hibernate.tool.hbm2ddl.SchemaExport.(SchemaExport.java:61)
at xhlh.ExportDB.main(ExportDB.java:10)
期待各位前辈帮忙解决，或者提出更好的设计方法！
[该贴被zidom于2009-03-03 15:38修改过]
[该贴被zidom于2009-03-03 15:39修改过]
[该贴被zidom于2009-03-03 15:58修改过]
[该贴被admin于2009-03-04 11:23修改过]