Grails 继承映射中的判别器问题

Question

我有 4 个类 A、B、B1、B2，其继承映射如下所述：
A（映射到表A）是最顶层的父类，其继承映射策略为tablePerHierarchy=false（表示其每个子类都映射到单个表）。
B 类继承自 A，B1、B2 继承自 B。但是 B1 和 B2 与 B 共享同一个表，因此在 B 类中，我声明 tablePerHierarchy=true 和一个区分器来分隔 B1 和 B2 .
详细代码在这里：

class A {
     static mapping = {
          tablePerHierarchy false
          table 'A'
     }
}

class B extends A {
     static mapping = {
          tablePerHierarchy true
          table 'B'
          discriminator column : 'TYPE'
     }
     String bProp1
     String bProp2
}

class B1 extends B {
     static mapping = {
          discriminator column : 'TYPE', value : 'B1'
     }
     String b1Props1 
     String b1Props2
}

class B2 extends B {
     static mapping = {
          discriminator column : 'TYPE', value : 'B2'
     }
     String b2Props1
     String b2Props1
}

当我启动我的应用程序时，发生错误：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'messageSource': Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting bean property 'sessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory': Invocation of init method failed; nested exception is org.hibernate.MappingException: No discriminator found for edu.test.B1. Discriminator is needed when 'single-table-per-hierarchy' is used and a class has subclasses
    at org.grails.tomcat.TomcatServer.start(TomcatServer.groovy:212)
    at grails.web.container.EmbeddableServer$start.call(Unknown Source)
    at _GrailsRun_groovy$_run_closure5_closure12.doCall(_GrailsRun_groovy:158)
    at _GrailsRun_groovy$_run_closure5_closure12.doCall(_GrailsRun_groovy)
    at _GrailsSettings_groovy$_run_closure10.doCall(_GrailsSettings_groovy:280)
    at _GrailsSettings_groovy$_run_closure10.call(_GrailsSettings_groovy)
    at _GrailsRun_groovy$_run_closure5.doCall(_GrailsRun_groovy:149)
    at _GrailsRun_groovy$_run_closure5.call(_GrailsRun_groovy)
    at _GrailsRun_groovy.runInline(_GrailsRun_groovy:116)
    at _GrailsRun_groovy.this$4$runInline(_GrailsRun_groovy)
    at _GrailsRun_groovy$_run_closure1.doCall(_GrailsRun_groovy:59)
    at RunApp$_run_closure1.doCall(RunApp:33)
    at gant.Gant$_dispatch_closure5.doCall(Gant.groovy:381)
    at gant.Gant$_dispatch_closure7.doCall(Gant.groovy:415)
    at gant.Gant$_dispatch_closure7.doCall(Gant.groovy)
    at gant.Gant.withBuildListeners(Gant.groovy:427)
    at gant.Gant.this$2$withBuildListeners(Gant.groovy)
    at gant.Gant$this$2$withBuildListeners.callCurrent(Unknown Source)
    at gant.Gant.dispatch(Gant.groovy:415)
    at gant.Gant.this$2$dispatch(Gant.groovy)
    at gant.Gant.invokeMethod(Gant.groovy)
    at gant.Gant.executeTargets(Gant.groovy:590)
    at gant.Gant.executeTargets(Gant.groovy:589)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting bean property 'sessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory': Invocation of init method failed; nested exception is org.hibernate.MappingException: No discriminator found for edu.test.B1. Discriminator is needed when 'single-table-per-hierarchy' is used and a class has subclasses
    ... 23 more
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory': Invocation of init method failed; nested exception is org.hibernate.MappingException: No discriminator found for edu.test.B1. Discriminator is needed when 'single-table-per-hierarchy' is used and a class has subclasses
    ... 23 more
Caused by: org.hibernate.MappingException: No discriminator found for edu.test.B1. Discriminator is needed when 'single-table-per-hierarchy' is used and a class has subclasses
    ... 23 more

我已按照Grails文档中有关鉴别器的说明进行操作（ http://grails.org/doc/latest/ref/Database%20Mapping/discriminator.html ）但它不起作用。我在这里找到了关于此文档问题的 JIRA： http://jira.grails.org/browse/ GRAILS-5168 并在他们评论时修复了我的代码，但仍然出现相同的错误。

我不知道导致这个问题的原因。 B 中的 tablePerHierarchy=true 是否会覆盖 A 中定义的策略？
你能帮我解决这个问题吗？太感谢了。

Answer 1

似乎并没有真正支持类层次结构的混合继承策略，甚至到 JPA/Hibernate 级别也是如此。
我认为您的问题与这些相同（或至少非常相似）：

通过 JPA 注释更改类层次结构分支中的继承策略

如何将继承策略与 JPA 注释和 Hibernate 混合使用？

如果将“org.codehaus.groovy.grails.orm.hibernate”的日志设置更改为“debug”，您可以看到B 类中的“tablePerHierarchy=true”设置不会覆盖 A 中的策略。无论如何，它不起作用。同样，它看起来是一个比 GORM 级别更低的限制。可以修改您的设计以对该层次结构使用一种继承策略吗？