InvalidOperationException当保存子对象与集合

Question

我有一个Foo类，具有ISet类型的属性。 Bar类又有一个Foo属性和一个MiniBars集。使用NHibernate我希望坚持一个Foo的实例，然后，但仍然在相同的NHibernate事务中，将Bar的实例添加到Foo对象的Bars属性，将Foo对象添加到Bar对象的Foo属性，然后当我提交事务时，Bar对象也会被持久化。

但是，我从NHibernate的某个地方得到一个Excepetion：“System.InvalidOperationException：集合被修改;枚举操作可能不会执行。”

我得出结论，这与MiniBars的ISet有关。在酒吧的默认构造函数这一集是使用

MiniBars = new HashedSet<MiniBar>(); 

如果我删除此行的代码，或删除Bar.hbm.xml的迷你吧属性的映射，一切工作像预想的那样。

的不工作代码：

using (var tx = session.BeginTransaction()) 
{ 
    Foo foo = new Foo(); 
    Foo.Id = 1; 
    session.Save(foo); 

    Bar bar = new Bar 
    { 
    Foo = foo; // The setter for Foo also adds Bar to the set Foo.Bars 
    } 

    tx.Commit(); // I wish this to save both foo and bar 
} 

抛出的异常的堆栈跟踪：

System.InvalidOperationException : Collection was modified; enumeration operation may not execute. 
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource) 
at System.Collections.Generic.List`1.Enumerator.MoveNextRare() 
at System.Collections.Generic.List`1.Enumerator.MoveNext() 
at NHibernate.Engine.Cascade.CascadeCollectionElements(Object child, CollectionType collectionType, CascadeStyle style, IType elemType, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs: line 231 
at NHibernate.Engine.Cascade.CascadeCollection(Object child, CascadeStyle style, Object anything, CollectionType type) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs: line 201 
at NHibernate.Engine.Cascade.CascadeAssociation(Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs: line 185 
at NHibernate.Engine.Cascade.CascadeProperty(Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs: line 148 
at NHibernate.Engine.Cascade.CascadeOn(IEntityPersister persister, Object parent, Object anything) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs: line 126 
at NHibernate.Event.Default.AbstractFlushingEventListener.CascadeOnFlush(IEventSource session, IEntityPersister persister, Object key, Object anything) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\AbstractFlushingEventListener.cs: line 207 
at NHibernate.Event.Default.AbstractFlushingEventListener.PrepareEntityFlushes(IEventSource session) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\AbstractFlushingEventListener.cs: line 195 
at NHibernate.Event.Default.AbstractFlushingEventListener.FlushEverythingToExecutions(FlushEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\AbstractFlushingEventListener.cs: line 48 
at NHibernate.Event.Default.DefaultFlushEventListener.OnFlush(FlushEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\DefaultFlushEventListener.cs: line 18 
at NHibernate.Impl.SessionImpl.Flush() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs: line 1472 
at NHibernate.Transaction.AdoTransaction.Commit() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Transaction\AdoTransaction.cs: line 187 
at Company.Product.Test.DatabaseDependentFixtureBase.FillDatabase() in DatabaseDependentFixtureBase.cs: line 121 
at Company.Product.Test.DatabaseDependentFixtureExample.Temp() in DatabaseDependentFixture.cs: line 40 

堆栈跟踪指出，从NHibernate.Engine.Cascade此功能：

private void CascadeCollectionElements(object child, CollectionType collectionType, CascadeStyle style, IType elemType, object anything, bool isCascadeDeleteEnabled) 
    { 
     // we can't cascade to non-embedded elements 
     bool embeddedElements = eventSource.EntityMode != EntityMode.Xml 
           || ((EntityType) collectionType.GetElementType(eventSource.Factory)).IsEmbeddedInXML; 

     bool reallyDoCascade = style.ReallyDoCascade(action) && embeddedElements 
           && child != CollectionType.UnfetchedCollection; 

     if (reallyDoCascade) 
     { 
      log.Info("cascade " + action + " for collection: " + collectionType.Role); 

      foreach (object o in action.GetCascadableChildrenIterator(eventSource, collectionType, child)) 
       CascadeProperty(o, elemType, style, anything, isCascadeDeleteEnabled); 

      log.Info("done cascade " + action + " for collection: " + collectionType.Role); 
     } 

     var childAsPersColl = child as IPersistentCollection; 
     bool deleteOrphans = style.HasOrphanDelete && action.DeleteOrphans && elemType.IsEntityType 
          && childAsPersColl != null; //a newly instantiated collection can't have orphans 

     if (deleteOrphans) 
     { 
      // handle orphaned entities!! 
      log.Info("deleting orphans for collection: " + collectionType.Role); 

      // we can do the cast since orphan-delete does not apply to: 
      // 1. newly instantiated collections 
      // 2. arrays (we can't track orphans for detached arrays) 
      string entityName = collectionType.GetAssociatedEntityName(eventSource.Factory); 
      DeleteOrphans(entityName, childAsPersColl); 

      log.Info("done deleting orphans for collection: " + collectionType.Role); 
     } 
    } 

在这个函数中有一个foreach循环，但我看不到在厕所内的集合被改变了页。我尽可能地遵循了方法调用，但是由于我没有查看过NHibernate源代码，所以它非常令人难以置信。

我想它可能是NHibernate中的一个错误，但我认为这更可能是我在使用NHibernate时出错。任何想法，将不胜感激！

Answer 1

所描述的错误发生在您正在枚举集合的过程中，并在此过程中尝试修改集合时。这里有这样一个例子：

List<string> someCollection = new List<string>(); 

someCollection.Add("Hello"); 
someCollection.Add("World"); 
someCollection.Add("Hello"); 
someCollection.Add("World"); 

// Enumerate the collection 
foreach (string item in someCollection) 
{ 
    // If the item is "World", remove it from the collection 
    if ("World".Equals(item)) 
    { 
     someCollection.Remove(item); // This will throw an InvalidOperationException. 
    } 
} 

在上面的例子中，当我们试图从收集我们在枚举过程中删除项目抛出异常。这是一个无效的操作。为了克服这个问题，你需要改变集合的修改方式。替代方法的例子是列举该集合的副本（即foreach (var item in someCollection.ToArray())）;或者直到枚举完成后才推迟收集修​​改。

我会建议看异常的来源（我将假设指向一些集合枚举），然后环视该点对该集合进行一些修改。