Question

我有一个类Foo，其属性类型为ISet。 Bar类又有一个Foo属性和一个MiniBars的ISet。使用NHibernate我希望保留一个Foo实例，然后，但仍然在同一个NHibernate事务中，将一个Bar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，也会看到Bar对象被保留。

但是，我从NHibernate内部的某处获得了一个Excepetion：“System.InvalidOperationException：Collection被修改;枚举操作可能无法执行。”

我得出结论，这与MiniBars的ISet有关。在Bar的默认构造函数中，此集使用

设置

MiniBars = new HashedSet<MiniBar>();

如果我删除这行代码，或从Bar.hbm.xml中删除MiniBars属性的映射，一切都按预期工作。

无效代码：

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

堆栈跟踪从NHibernate.Engine.Cascade：

指出了这个函数

    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);
        }
    }

此函数中有一个foreach循环，但我看不到集合在循环中被更改。我尽可能地遵循方法调用，但由于我之前没有查看NHibernate源代码，所以它非常压倒性。

我猜它可能是NHibernate中的一个错误，但我认为在使用NHibernate时我更有可能做错了。任何想法将不胜感激！

Answer 1

当您正在对集合进行枚举并继续尝试修改集合时，会出现您所描述的错误。这是一个例子：

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.
    }
}

在上面的示例中，当我们尝试从枚举过程中的集合中删除项时，抛出异常。这是一个无效的操作。要解决此问题，您需要更改集合的修改方式。替代方法的例子是枚举集合的副本（即foreach (var item in someCollection.ToArray())）;或者在完成枚举之后延迟收集修改。

我建议查看异常的来源（我将假设指向一些集合枚举），然后环顾这一点以对该集合进行一些修改。

使用集合保存子对象时出现InvalidOperationException

1 个答案: