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由于IDBasyncEnumable错误,无法使用实体框架查询数据库

entity-framework c#

user8128167 · 技术社区 · 7 年前

System.InvalidOperationException系统无效操作异常发生

消息=源IQueryable未实现IDbAsyncEnumerable。只有实现IDbAsyncEnumerable的源才能用于实体框架异步操作。有关详细信息,请参见 http://go.microsoft.com/fwlink/?LinkId=287068

源=实体框架

堆栈跟踪: 1 source) at System.Data.Entity.QueryableExtensions.ToListAsync[TSource](IQueryable 1个来源)
在C:\ Projects\MyApp\MyApp Model\Cpr.Apps.Tam.Model\Utilities\DataSnapshot.cs:line 160中的Cpr.Apps.Tam.Model.Utilities.Utilities.Utilities.DataSnapshot`1.d|u18.MoveNext()

内部异常:

所以我尝试使用这个代码(参见 @Tony O'Hagan's 回答 IDbAsyncEnumerable not implemented ,从他引用的页面来看, https://msdn.microsoft.com/en-us/data/dn314429#async ):

public static class AsyncQueryableExtensions
{
    public static IQueryable<TElement> AsAsyncQueryable<TElement>(this IEnumerable<TElement> source)
    {
        return new DbAsyncEnumerable<TElement>(source);
    }

    public static IDbAsyncEnumerable<TElement> AsDbAsyncEnumerable<TElement>(this IEnumerable<TElement> source)
    {
        return new DbAsyncEnumerable<TElement>(source);
    }

    public static EnumerableQuery<TElement> AsAsyncEnumerableQuery<TElement>(this IEnumerable<TElement> source)
    {
        return new DbAsyncEnumerable<TElement>(source);
    }

    public static IQueryable<TElement> AsAsyncQueryable<TElement>(this Expression expression)
    {
        return new DbAsyncEnumerable<TElement>(expression);
    }

    public static IDbAsyncEnumerable<TElement> AsDbAsyncEnumerable<TElement>(this Expression expression)
    {
        return new DbAsyncEnumerable<TElement>(expression);
    }

    public static EnumerableQuery<TElement> AsAsyncEnumerableQuery<TElement>(this Expression expression)
    {
        return new DbAsyncEnumerable<TElement>(expression);
    }
}

internal class DbAsyncQueryProvider<TEntity> : IDbAsyncQueryProvider
{
    private readonly IQueryProvider _inner;

    internal DbAsyncQueryProvider(IQueryProvider inner)
    {
        _inner = inner;
    }

    public IQueryable CreateQuery(Expression expression)
    {
        return new DbAsyncEnumerable<TEntity>(expression);
    }

    public IQueryable<TElement> CreateQuery<TElement>(Expression expression)
    {
        return new DbAsyncEnumerable<TElement>(expression);
    }

    public object Execute(Expression expression)
    {
        return _inner.Execute(expression);
    }

    public TResult Execute<TResult>(Expression expression)
    {
        return _inner.Execute<TResult>(expression);
    }

    public Task<object> ExecuteAsync(Expression expression, CancellationToken cancellationToken)
    {
        return Task.FromResult(Execute(expression));
    }

    public Task<TResult> ExecuteAsync<TResult>(Expression expression, CancellationToken cancellationToken)
    {
        return Task.FromResult(Execute<TResult>(expression));
    }
}

internal class DbAsyncEnumerable<T> : EnumerableQuery<T>, IDbAsyncEnumerable<T>, IQueryable<T>
{
    public DbAsyncEnumerable(IEnumerable<T> enumerable)
        : base(enumerable)
    { }

    public DbAsyncEnumerable(Expression expression)
        : base(expression)
    { }

    public IDbAsyncEnumerator<T> GetAsyncEnumerator()
    {
        return new DbAsyncEnumerator<T>(this.AsEnumerable().GetEnumerator());
    }

    IDbAsyncEnumerator IDbAsyncEnumerable.GetAsyncEnumerator()
    {
        return GetAsyncEnumerator();
    }

    IQueryProvider IQueryable.Provider
    {
        get { return new DbAsyncQueryProvider<T>(this); }
    }
}

internal class DbAsyncEnumerator<T> : IDbAsyncEnumerator<T>
{
    private readonly IEnumerator<T> _inner;

    public DbAsyncEnumerator(IEnumerator<T> inner)
    {
        _inner = inner;
    }

    public void Dispose()
    {
        _inner.Dispose();
    }

    public Task<bool> MoveNextAsync(CancellationToken cancellationToken)
    {
        return Task.FromResult(_inner.MoveNext());
    }

    public T Current
    {
        get { return _inner.Current; }
    }

    object IDbAsyncEnumerator.Current
    {
        get { return Current; }
    }
}

请注意,我得到以下错误:

System.NullReferenceException异常用户代码HResult=-2147467261未处理消息=对象引用未设置为对象的实例。

at lambda_方法(关闭,缺陷总结)
在System.Linq.Enumerable.WhereListIterator 1.MoveNext() at System.Linq.Enumerable.<DistinctIterator>d__64 1.移动下一个()
在System.Linq.Buffer 1..ctor(IEnumerable 1个来源)
在System.Linq.OrderedEnumerable 1.<GetEnumerator>d__1.MoveNext() at System.Linq.Enumerable.<DistinctIterator>d__64 1.移动下一个()
在System.Linq.Enumerable.dúu 25 1.MoveNext() at MyApp.Model.Utilities.DbAsyncEnumerator 1.将MoveNextAsync(CancellationToken CancellationToken)放在C:\ Projects\MyApp\Model\Utilities\AsyncQueryableExtensions.cs:line 125中
在System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.d|u 5`1.MoveNext()内部异常:

有人建议我如何找到导致异常的空值吗?它发生在这个函数中:

    public Task<bool> MoveNextAsync(CancellationToken cancellationToken)
    {
        return Task.FromResult(_inner.MoveNext());
    }

当我检查内部时,不清楚变量的哪个部分导致了空错误:

-       _inner  {System.Linq.Enumerable.<TakeIterator>d__25<MyApp.Model.Entities.DefectSummary>}    System.Collections.Generic.IEnumerator<MyApp.Model.Entities.DefectSummary> {System.Linq.Enumerable.<TakeIterator>d__25<MyApp.Model.Entities.DefectSummary>}
+       Non-Public members      
-       Results View    Expanding the Results View will enumerate the IEnumerable   
-       Data    {System.Collections.ListDictionaryInternal} System.Collections.IDictionary {System.Collections.ListDictionaryInternal}
        Count   0   int
        IsFixedSize false   bool
        IsReadOnly  false   bool
        IsSynchronized  false   bool
-       Keys    {System.Collections.ListDictionaryInternal.NodeKeyValueCollection}  System.Collections.ICollection {System.Collections.ListDictionaryInternal.NodeKeyValueCollection}
+       Non-Public members      
-       Results View    Expanding the Results View will enumerate the IEnumerable   
        Empty   "Enumeration yielded no results"    string
        SyncRoot    {object}    object
+       Values  {System.Collections.ListDictionaryInternal.NodeKeyValueCollection}  System.Collections.ICollection {System.Collections.ListDictionaryInternal.NodeKeyValueCollection}
+       Non-Public members      
+       Results View    Expanding the Results View will enumerate the IEnumerable   
        HResult -2147467261 int
        HelpLink    null    string
+       InnerException  null    System.Exception
        Message "Object reference not set to an instance of an object." string
        Source  "Anonymously Hosted DynamicMethods Assembly"    string
        StackTrace  "   at lambda_method(Closure , DefectSummary )\r\n   at System.Linq.Enumerable.WhereListIterator`1.MoveNext()\r\n   at System.Linq.Enumerable.<DistinctIterator>d__64`1.MoveNext()\r\n   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)\r\n   at System.Linq.OrderedEnumerable`1.<GetEnumerator>d__1.MoveNext()\r\n   at System.Linq.Enumerable.<DistinctIterator>d__64`1.MoveNext()\r\n   at System.Linq.Enumerable.<TakeIterator>d__25`1.MoveNext()\r\n   at System.Linq.SystemCore_EnumerableDebugView`1.get_Items()"   string
+       TargetSite  {Boolean lambda_method(System.Runtime.CompilerServices.Closure, MyApp.Model.Entities.DefectSummary)}    System.Reflection.MethodBase {System.Reflection.Emit.DynamicMethod.RTDynamicMethod}
+       Static members      
+       Non-Public members

更新:

    public IQueryable<Defect> GetLoadQuery()
    {
        IQueryable<Defect> query = null;
        // Call to stored procedure GetDefects
        var defectList = DbContext.GetDefects(null, null).ToList();
        var defects = new List<Defect>();

        using (IDefectDataService dataService = ServiceLocator.Current.GetInstance<IDefectDataService>())
        {
            foreach (var i in defectList)
            {
                dataService.DefectId = i.NotificationNo;
                NotificationLinearAsset notificationLam = dataService.GetNotificationLinearAsset();
                decimal? startPoint = notificationLam.StartPoint;
                decimal? endPoint = notificationLam.EndPoint;
                defects .Add(new Defect()
                {
                    NotificationNo = i.NotificationNo,
                    Priority = i.Priority,
                    ReportedBy = i.ReportedBy,
                    MeasuringDocument = i.MeasuringDocument,
                    AssetTypeDescription = i.AssetTypeDescription,
                    StartPoint = startPoint,
                    EndPoint = endPoint,
                    Description = i.Description,
                    AssetId = i.AssetId,
                });
            }
            query = defectSummaries.AsQueryable();
            // Other code here for filtering results...
        }

        return query.AsAsyncQueryable();
    }

更新2:

                //StartPoint = startPoint,
                //EndPoint = endPoint,

foreach 停止,如果 startPoint endPoint 为空,调试器从不停止。

更新3:

谢谢你的建议, @Ivan Stoev StartPoint/EndPoint ,而且它没有错误,所以我不确定这是为什么。可能是Visual Studio中缓存了某些内容?

1 回复 | 直到 7 年前

user8128167 7 年前

通过不使用存储过程结果来解决该问题,存储过程结果将创建 GetDefect_Result Defect 上面的MVVM应用程序要使用的类型 foreach 键入结果。此解决方案还涉及删除对 IDbAsyncEnumerable .

    public IQueryable<Defect> GetLoadQuery()
    {
        IDbSet<Defect> dbSet = DbContext.Defects;

        IQueryable<Defect> query = dbSet.AsQueryable();

        // Other code here for filtering results...
        return query;
    }