已经有一个打开的DataReader与此命令相关联，必须先关闭它

我有这个查询，我得到了这个函数的错误:

var accounts = from account in context.Accounts
               from guranteer in account.Gurantors
               select new AccountsReport
               {
                   CreditRegistryId = account.CreditRegistryId,
                   AccountNumber = account.AccountNo,
                   DateOpened = account.DateOpened,
               };

 return accounts.AsEnumerable()
                .Select((account, index) => new AccountsReport()
                    {
                        RecordNumber = FormattedRowNumber(account, index + 1),
                        CreditRegistryId = account.CreditRegistryId,
                        DateLastUpdated = DateLastUpdated(account.CreditRegistryId, account.AccountNumber),
                        AccountNumber = FormattedAccountNumber(account.AccountType, account.AccountNumber)
                    })
                .OrderBy(c=>c.FormattedRecordNumber)
                .ThenByDescending(c => c.StateChangeDate);


public DateTime DateLastUpdated(long creditorRegistryId, string accountNo)
{
    return (from h in context.AccountHistory
            where h.CreditorRegistryId == creditorRegistryId && h.AccountNo == accountNo
            select h.LastUpdated).Max();
}

错误:

已经有一个打开的DataReader与此命令相关联，必须先关闭它。

更新:

添加堆栈跟踪:

InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first.]
   System.Data.SqlClient.SqlInternalConnectionTds.ValidateConnectionForExecute(SqlCommand command) +5008639
   System.Data.SqlClient.SqlConnection.ValidateConnectionForExecute(String method, SqlCommand command) +23
   System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async) +144
   System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) +87
   System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) +32
   System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method) +141
   System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior) +12
   System.Data.Common.DbCommand.ExecuteReader(CommandBehavior behavior) +10
   System.Data.EntityClient.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior) +443

[EntityCommandExecutionException: An error occurred while executing the command definition. See the inner exception for details.]
   System.Data.EntityClient.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior) +479
   System.Data.Objects.Internal.ObjectQueryExecutionPlan.Execute(ObjectContext context, ObjectParameterCollection parameterValues) +683
   System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption) +119
   System.Data.Objects.ObjectQuery`1.System.Collections.Generic.IEnumerable<T>.GetEnumerator() +38
   System.Linq.Enumerable.Single(IEnumerable`1 source) +114
   System.Data.Objects.ELinq.ObjectQueryProvider.<GetElementFunction>b__3(IEnumerable`1 sequence) +4
   System.Data.Objects.ELinq.ObjectQueryProvider.ExecuteSingle(IEnumerable`1 query, Expression queryRoot) +29
   System.Data.Objects.ELinq.ObjectQueryProvider.System.Linq.IQueryProvider.Execute(Expression expression) +91
   System.Data.Entity.Internal.Linq.DbQueryProvider.Execute(Expression expression) +69
   System.Linq.Queryable.Max(IQueryable`1 source) +216
   CreditRegistry.Repositories.CreditRegistryRepository.DateLastUpdated(Int64 creditorRegistryId, String accountNo) in D:\Freelance Work\SuperExpert\CreditRegistry\CreditRegistry\Repositories\CreditRegistryRepository.cs:1497
   CreditRegistry.Repositories.CreditRegistryRepository.<AccountDetails>b__88(AccountsReport account, Int32 index) in D:\Freelance Work\SuperExpert\CreditRegistry\CreditRegistry\Repositories\CreditRegistryRepository.cs:1250
   System.Linq.<SelectIterator>d__7`2.MoveNext() +198
   System.Linq.Buffer`1..ctor(IEnumerable`1 source) +217
   System.Linq.<GetEnumerator>d__0.MoveNext() +96

当前回答

我通过改变解决了这个问题等待_accountSessionDataModel.SaveChangesAsync (); 来 _accountSessionDataModel.SaveChanges (); 在我的Repository类中。

 public async Task<Session> CreateSession()
    {
        var session = new Session();

        _accountSessionDataModel.Sessions.Add(session);
        await _accountSessionDataModel.SaveChangesAsync();
     }

改为:

 public Session CreateSession()
    {
        var session = new Session();

        _accountSessionDataModel.Sessions.Add(session);
        _accountSessionDataModel.SaveChanges();
     }

问题是我在创建会话(在代码中)后在前端更新了会话，但由于SaveChangesAsync是异步发生的，获取会话导致了这个错误，因为显然SaveChangesAsync操作还没有准备好。

2017-07-21 14:01:06

其他回答

看起来您正在使用相同的EF上下文从活动查询中调用DateLastUpdate，并且DateLastUpdate向数据存储本身发出命令。实体框架一次只支持每个上下文一个活动命令。

你可以把上面的两个查询重构成一个:

return accounts.AsEnumerable()
       .Select((account, index) => new AccountsReport()
       {
         RecordNumber = FormattedRowNumber(account, index + 1),
         CreditRegistryId = account.CreditRegistryId,
         DateLastUpdated = (
             from h in context.AccountHistory 
             where h.CreditorRegistryId == creditorRegistryId && h.AccountNo == accountNo 
             select h.LastUpdated
         ).Max(),
         AccountNumber = FormattedAccountNumber(account.AccountType, account.AccountNumber)
       })
       .OrderBy(c=>c.FormattedRecordNumber)
       .ThenByDescending(c => c.StateChangeDate);

我还注意到您在查询中调用了FormattedAccountNumber和FormattedRecordNumber这样的函数。除非这些是存储的proc或函数，您已经从数据库导入到实体数据模型并映射正确，否则这些也将抛出异常，因为EF将不知道如何将这些函数转换为可以发送到数据存储的语句。

还要注意，调用AsEnumerable并不强制执行查询。直到查询执行被推迟到枚举为止。如果需要，可以使用ToList或ToArray强制枚举。

2011-05-19 17:19:24

在我的例子中，使用Include()解决了这个错误，并且根据情况可以更有效地发出多个查询，当它可以通过连接一次性查询时。

IEnumerable<User> users = db.Users.Include("Projects.Tasks.Messages");

foreach (User user in users)
{
    Console.WriteLine(user.Name);
    foreach (Project project in user.Projects)
    {
        Console.WriteLine("\t"+project.Name);
        foreach (Task task in project.Tasks)
        {
            Console.WriteLine("\t\t" + task.Subject);
            foreach (Message message in task.Messages)
            {
                Console.WriteLine("\t\t\t" + message.Text);
            }
        }
    }
}

2013-04-15 07:05:08

我通过改变解决了这个问题等待_accountSessionDataModel.SaveChangesAsync (); 来 _accountSessionDataModel.SaveChanges (); 在我的Repository类中。

 public async Task<Session> CreateSession()
    {
        var session = new Session();

        _accountSessionDataModel.Sessions.Add(session);
        await _accountSessionDataModel.SaveChangesAsync();
     }

改为:

 public Session CreateSession()
    {
        var session = new Session();

        _accountSessionDataModel.Sessions.Add(session);
        _accountSessionDataModel.SaveChanges();
     }

2017-07-21 14:01:06

对于那些通过谷歌找到这个的人; 我得到这个错误是因为，正如错误所建议的那样，我未能在相同的SqlCommand上创建另一个SqlDataReader之前关闭一个SqlDataReader，错误地假设它将在离开创建它的方法时被垃圾收集。

我通过调用sqlDataReader.Close()解决了这个问题;在创建第二个读取器之前。

2017-07-21 18:01:22

在我的例子中，我从数据上下文中打开了一个查询，比如

    Dim stores = DataContext.Stores _
        .Where(Function(d) filter.Contains(d.code)) _

．.．然后又问了同样的问题…

    Dim stores = DataContext.Stores _
        .Where(Function(d) filter.Contains(d.code)).ToList

向第一个添加. tolist解决了我的问题。我认为将其包装在属性中是有意义的:

Public ReadOnly Property Stores As List(Of Store)
    Get
        If _stores Is Nothing Then
            _stores = DataContext.Stores _
                .Where(Function(d) Filters.Contains(d.code)).ToList
        End If
        Return _stores
    End Get
End Property

其中_stores是一个私有变量，Filters也是一个从AppSettings读取的只读属性。

2018-03-12 16:17:03

已经有一个打开的DataReader与此命令相关联，必须先关闭它

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