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

可以在return语句之前使用ToList()方法。

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)
       .ToList();


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

2013-01-14 11:27:17

其他回答

我在我的工具中使用web服务，这些服务获取存储过程。当越来越多的客户端工具获取web服务时，这个问题就出现了。我通过为这些函数指定Synchronized属性来修复存储过程。现在它工作良好，错误从未出现在我的工具。

 [MethodImpl(MethodImplOptions.Synchronized)]
 public static List<t> MyDBFunction(string parameter1)
  {
  }

此属性允许一次处理一个请求。这就解决了问题。

2015-12-28 04:10:36

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，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

在我的例子中，我必须在连接字符串中将MultipleActiveResultSets设置为True。然后出现了另一个错误(真正的错误)，关于不能在同一数据上下文中同时运行2个(SQL)命令!(EF核心，代码优先) 因此，我的解决方案是寻找任何其他异步命令执行，并将它们转换为同步命令，因为两个命令都只有一个DbContext。

我希望这对你有所帮助

2019-03-05 20:23:20

这是从一个真实的场景中提取出来的:

代码在连接字符串中设置MultipleActiveResultSets的Stage环境中工作良好发布到生产环境的代码没有MultipleActiveResultSets=true 如此多的页面/呼叫工作，而一个是失败的仔细查看调用，有一个对db的不必要调用，需要删除在Production中设置MultipleActiveResultSets=true，并发布清理过的代码，一切都能正常有效地工作

总之，不要忘记MultipleActiveResultSets，在发现冗余的db调用之前，代码可能已经运行了很长一段时间，这可能是非常昂贵的，我建议不要完全依赖于设置MultipleActiveResultSets属性，但也要找出为什么代码需要它失败的地方。

2017-09-06 17:54:02

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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