Grails 我如何实施单向一对多关系？
我有以下结构Grails 我如何实施单向一对多关系？,grails,gorm,one-to-many,Grails,Gorm,One To Many,我有以下结构 class User { String fname String lname String email static constraints = { fname(nullable:true, maxSize:30) fname(nullable:true, maxSize:30) email(nullable: true, email: true) } } class A exten
class User {
String fname
String lname
String email
static constraints = {
fname(nullable:true, maxSize:30)
fname(nullable:true, maxSize:30)
email(nullable: true, email: true)
}
}
class A extends User{
String smtng
List bInstance = new ArrayList()
static hasMany = [b : B]
static constraints = {
smtng(blank : true)
b(nullable : true)
}
}
class B {
String smtng1
String smtng2
static constraints = {
smtng1(blank:true, maxSize:50)
smtng2(blank:true, maxSize:50)
}
}
2014-09-03 12:37:11,010 [localhost-startStop-1] ERROR StackTrace - Full Stack Trace:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1512)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:521)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:458)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:296)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:293)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:610)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479)
at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:410)
at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306)
at org.codehaus.groovy.grails.web.context.GrailsContextLoader.initWebApplicationContext(GrailsContextLoader.java:70)
at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:112)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4973)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5467)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at org.codehaus.groovy.grails.commons.DefaultGrailsDomainClass.establishRelationshipForCollection(DefaultGrailsDomainClass.java:362)
at org.codehaus.groovy.grails.commons.DefaultGrailsDomainClass.establishRelationships(DefaultGrailsDomainClass.java:262)
at org.codehaus.groovy.grails.commons.DefaultGrailsDomainClass.<init>(DefaultGrailsDomainClass.java:120)
at org.codehaus.groovy.grails.commons.DomainClassArtefactHandler.newArtefactClass(DomainClassArtefactHandler.java:54)
at org.codehaus.groovy.grails.commons.AnnotationDomainClassArtefactHandler.newArtefactClass(AnnotationDomainClassArtefactHandler.java:54)
at org.codehaus.groovy.grails.commons.DefaultGrailsApplication.addArtefact(DefaultGrailsApplication.java:812)
at org.codehaus.groovy.grails.commons.DefaultGrailsApplication.addArtefact(DefaultGrailsApplication.java:538)
at org.codehaus.groovy.grails.commons.DefaultGrailsApplication.configureLoadedClasses(DefaultGrailsApplication.java:259)
at org.codehaus.groovy.grails.commons.DefaultGrailsApplication.initialise(DefaultGrailsApplication.java:743)
at org.codehaus.groovy.grails.plugins.GrailsPluginManagerFactoryBean.afterPropertiesSet(GrailsPluginManagerFactoryBean.java:123)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1571)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1509)
... 23 more
2014-09-03 12:37:11,015 [localhost-startStop-1] ERROR StackTrace - Full Stack Trace:
org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at org.codehaus.groovy.grails.commons.DefaultGrailsDomainClass.establishRelationshipForCollection(DefaultGrailsDomainClass.java:362)
at org.codehaus.groovy.grails.commons.DefaultGrailsDomainClass.establishRelationships(DefaultGrailsDomainClass.java:262)
at org.codehaus.groovy.grails.commons.DefaultGrailsDomainClass.<init>(DefaultGrailsDomainClass.java:120)
at org.codehaus.groovy.grails.commons.DomainClassArtefactHandler.newArtefactClass(DomainClassArtefactHandler.java:54)
at org.codehaus.groovy.grails.commons.AnnotationDomainClassArtefactHandler.newArtefactClass(AnnotationDomainClassArtefactHandler.java:54)
at org.codehaus.groovy.grails.commons.DefaultGrailsApplication.addArtefact(DefaultGrailsApplication.java:812)
at org.codehaus.groovy.grails.commons.DefaultGrailsApplication.addArtefact(DefaultGrailsApplication.java:538)
at org.codehaus.groovy.grails.commons.DefaultGrailsApplication.configureLoadedClasses(DefaultGrailsApplication.java:259)
at org.codehaus.groovy.grails.commons.DefaultGrailsApplication.initialise(DefaultGrailsApplication.java:743)
at org.codehaus.groovy.grails.plugins.GrailsPluginManagerFactoryBean.afterPropertiesSet(GrailsPluginManagerFactoryBean.java:123)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1571)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1509)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:521)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:458)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:296)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:293)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:610)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479)
at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:410)
at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306)
at org.codehaus.groovy.grails.web.context.GrailsContextLoader.initWebApplicationContext(GrailsContextLoader.java:70)
at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:112)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4973)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5467)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
2014-09-03 12:37:11,018 [localhost-startStop-1] ERROR StackTrace - Full Stack Trace:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
... 5 more
2014-09-03 12:37:11,020 [localhost-startStop-1] ERROR StackTrace - Full Stack Trace:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
... 5 more
2014-09-03 12:37:11,022 [localhost-startStop-1] ERROR StackTrace - Full Stack Trace:
org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
2014-09-03 12:37:11,023 [localhost-startStop-1] ERROR StackTrace - Full Stack Trace:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
... 5 more
2014-09-03 12:37:11,024 [localhost-startStop-1] ERROR StackTrace - Full Stack Trace:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
... 5 more
2014-09-03 12:37:11,026 [localhost-startStop-1] ERROR StackTrace - Full Stack Trace:
org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
2014-09-03 12:37:11,027 [localhost-startStop-1] ERROR StackTrace - Full Stack Trace:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [b] in class [class A] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [a] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [b:'myprop']
... 5 more
2014-09-03 12:37:11010[localhost-startStop-1]错误堆栈跟踪-完整堆栈跟踪：
org.springframework.beans.factory.BeanCreationException:使用ServletContext资源[/WEB-INF/applicationContext.xml]中定义的名称“pluginManager”创建bean时出错：调用init方法失败；嵌套的异常是org.codehaus.groovy.grails.exceptions.GrailsDomainException:class[class A]中的属性[b]是双向的一对多，其反面有两个可能的属性。命名关系另一端的一个属性[a]，或使用“mappedBy”静态定义映射关系的属性。示例：静态mappedBy=[b:'myprop']
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean（AbstractAutowireCapableBeanFactory.java:1512）
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean（AbstractAutowireCapableBeanFactory.java:521）
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean（AbstractAutowireCapableBeanFactory.java:458）
位于org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject（AbstractBeanFactory.java:296）
位于org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton（DefaultSingletonBeanRegistry.java:223）
位于org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean（AbstractBeanFactory.java:293）
位于org.springframework.beans.factory.support.AbstractBeanFactory.getBean（AbstractBeanFactory.java:194）
位于org.springframework.beans.factory.support.DefaultListableBeanFactory.PreInstanceSingleton（DefaultListableBeanFactory.java:610）
位于org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization（AbstractApplicationContext.java:932）
位于org.springframework.context.support.AbstractApplicationContext.refresh（AbstractApplicationContext.java:479）
位于org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext（ContextLoader.java:410）
位于org.springframework.web.context.ContextLoader.initWebApplicationContext（ContextLoader.java:306）
位于org.codehaus.groovy.grails.web.context.GrailContextLoader.initWebApplicationContext（grailContextLoader.java:70）
位于org.springframework.web.context.ContextLoaderListener.contextInitialized（ContextLoaderListener.java:112）
位于org.apache.catalina.core.StandardContext.listenerStart（StandardContext.java:4973）
位于org.apache.catalina.core.StandardContext.startInternal（StandardContext.java:5467）
位于org.apache.catalina.util.LifecycleBase.start（LifecycleBase.java:150）
位于org.apache.catalina.core.ContainerBase$StartChild.call（ContainerBase.java:1559）
位于org.apache.catalina.core.ContainerBase$StartChild.call（ContainerBase.java:1549）
位于java.util.concurrent.FutureTask$Sync.innerRun（FutureTask.java:303）
位于java.util.concurrent.FutureTask.run（FutureTask.java:138）
位于java.util.concurrent.ThreadPoolExecutor$Worker.runTask（ThreadPoolExecutor.java:886）
位于java.util.concurrent.ThreadPoolExecutor$Worker.run（ThreadPoolExecutor.java:908）
运行（Thread.java:662）
由：org.codehaus.groovy.grails.exceptions.GrailsDomainException引起的：类[class A]中的属性[b]是双向的一对多，其反面有两个可能的属性。命名关系另一端的一个属性[a]，或使用“mappedBy”静态定义映射关系的属性。示例：静态mappedBy=[b:'myprop']
位于org.codehaus.groovy.grails.commons.DefaultGrailsDomainClass.EstablisationshipForCollection（DefaultGrailsDomainClass.java:362）
位于org.codehaus.groovy.grails.commons.DefaultGrailDomainClass.establishRelationships（DefaultGrailDomainClass.java:262）
位于org.codehaus.groovy.grails.commons.DefaultGrailDomainClass。（DefaultGrailDomainClass.java:120）
位于org.codehaus.groovy.grails.commons.DomainClassArtefactHandler.newArtefactClass（DomainClassArtefactHandler.java:54）
位于org.codehaus.groovy.grails.commons.AnnotationDomainClassArtefactHandler.newArtefactClass（AnnotationDomainClassArtefactHandler.java:54）
位于org.codehaus.groovy.grails.commons.DefaultGrailsApplication.addArtefact（DefaultGrailsApplication.java:812）
位于org.codehaus.groovy.grails.commons.DefaultGrailsApplication.addArtefact（DefaultGrailsApplication.java:538）
位于org.codehaus.groovy.grails.commons.DefaultGrailsApplication.configureLoadedClasses（DefaultGrailsApplication.java:259）
位于org.codehaus.groovy.grails.commons.DefaultGrailsApplication.initialise（DefaultGrailsApplication.java:743）
位于org.codehaus.groovy.grails.plugins.GrailsPluginManagerFactoryBean.AfterPropertieSet（GrailsPluginManagerFactoryBean.java:123）
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods（AbstractAutowireCapableBeanFactory.java:1571）
位于org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean（AbstractAutowireCapableBeanFactory.java:1509）
... 23多
2014-09-03 12:37:11015[localhost-startStop-1]错误堆栈跟踪-完整堆栈跟踪：
org.codehaus.groovy.grails.exceptions.GrailsDomainException:class[class A]中的属性[b]是双向的一对多，其反面有两个可能的属性。命名关系另一端的一个属性[a]，或使用“mappedBy”静态定义映射关系的属性。示例：静态mappedBy=[b:'myprop']
位于org.codehaus.groovy.grails.commons.DefaultGrailsDomainClass.EstablisationshipForCollection（DefaultGrailsDomainClass.java:362）
位于org.codehaus.groovy.grails.commons.DefaultGrailsDom
class A extends User{
String smtng
List bInstance
static hasMany = [bInstance : B]
static constraints = {
bInstance(nullable : true)
}
}
class B {
String smtng1
String smtng2
static belongsTo = [A]
}
class A extends user{
static hasMany = [bInstance : B]
static mappedBy = [ B:'bref' ]
}
class B {
static belongsTo = [ a:A ]
}
class A extends User{
String smtng
List b // note: do not include an initializer expression here
static hasMany = [b : B]
static mappedBy = [b:"none"]
static constraints = {
smtng(blank : true)
b(nullable : true)
}
}