错误:“无法同时提取多个包"调用Configuration.BuildSessionFactory()时; [英] Error: "Cannot simultaneously fetch multiple bags" when calling Configuration.BuildSessionFactory();
问题描述
升级到NHibernate 2.1后,我们会收到此错误.
We are getting this error after upgrading to NHibernate 2.1.
[QueryException: Cannot simultaneously fetch multiple bags.]
NHibernate.Loader.BasicLoader.PostInstantiate() +418
NHibernate.Loader.Entity.EntityLoader..ctor(IOuterJoinLoadable persister, String[] uniqueKey, IType uniqueKeyType, Int32 batchSize, LockMode lockMode, ISessionFactoryImplementor factory, IDictionary`2 enabledFilters) +123
NHibernate.Loader.Entity.BatchingEntityLoader.CreateBatchingEntityLoader(IOuterJoinLoadable persister, Int32 maxBatchSize, LockMode lockMode, ISessionFactoryImplementor factory, IDictionary`2 enabledFilters) +263
NHibernate.Persister.Entity.AbstractEntityPersister.CreateEntityLoader(LockMode lockMode, IDictionary`2 enabledFilters) +26
NHibernate.Persister.Entity.AbstractEntityPersister.CreateLoaders() +57
NHibernate.Persister.Entity.AbstractEntityPersister.PostInstantiate() +1244
NHibernate.Persister.Entity.SingleTableEntityPersister.PostInstantiate() +18
NHibernate.Impl.SessionFactoryImpl..ctor(Configuration cfg, IMapping mapping, Settings settings, EventListeners listeners) +3261
NHibernate.Cfg.Configuration.BuildSessionFactory() +87
在没有进入NHibernate源代码的情况下,我似乎看不到是哪个映射导致了问题.
Without stepping into the NHibernate source, it doesn't look like I can see which mapping is creating the issue.
这是一个非常老的应用程序,其中包含大量映射文件,许多映射中都有一对多的包,所有这些都被实例化了.
It's a very old application with a load of mappings files, lots of mappings have one-to-many bags in them, all lazy instantiated.
例如:
<bag name="Ownership" lazy="true" cascade="all" inverse="true" outer-join="auto" where="fkOwnershipStatusID!=6">
<key column="fkStakeHolderID"/>
<one-to-many class="StakeholderLib.Ownership,StakeholderLib" />
</bag>
映射到:
public virtual IList Ownership {
get {
if (ownership == null)
ownership = new ArrayList();
return ownership;
}
set { ownership = value; }
}
有人在升级到NHibernate 2.1之前见过此错误吗?
Has anyone seen this error before when upgrading to NHibernate 2.1?
推荐答案
我们最终找到了答案...
We found the answer eventually...
我们有一个实体,其中有一个以上的袋子,并且具有多对多关系
We had an entity that had more than 1 bag with a many to many relationship that had
outer-join="true"
设置.
这引起了错误,因为设置外部联接获取时通常这样做是为了限制db往返,从而使nHibernate能够在1个select中检索整个关联.在这种情况下,这将导致在每个袋子上进行预取,立即导致错误.
This caused the error because when you set outer-join fetching you usually do this to limit the db round-trips, enabling nHibernate to retrieve the whole association in 1 select. In this circumstance this will cause a pre-fetch on each bag immediately causing the error.
我们将其更改为"outer-join ="auto"(如下所示),并且它们不再被预取.这阻止了nHibernate尝试同时获取多个包的操作.
We changed that to outer-join="auto" (as below) and they stopped being pre-fetched. This stopped nHibernate attempting to fetch multiple bags simultaneously.
<bag name="Groups" lazy="true" cascade="none" table="dbname..tablename">
<key column="foreignkeyname" />
<many-to-many class="classname.typename,assemblyname"
column="foreignkeyname" outer-join="auto" />
</bag>
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