已经有与此命令关联的打开的DataReader，必须首先关闭

我有此查询，而且出现此函数错误：

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();
}

错误是：

已经有一个与此命令相关联的打开的DataReader，必须先关闭它。

更新：

堆栈跟踪已添加：

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

---

#1楼

您能够在return语句以前使用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;
    }

---

#2楼

在个人状况下，使用Include()解决了该错误，而且根据状况，若是能够经过联接同时查询全部查询，则发出多个查询的效率要高得多。

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);
            }
        }
    }
}

---

#3楼

我不知道这是不是重复的答案。 若是是这样，我很抱歉。 我只想让有须要的人知道如何使用ToList（）解决问题。

就我而言，下面的查询有相同的异常。

int id = adjustmentContext.InformationRequestOrderLinks.Where(item => item.OrderNumber == irOrderLinkVO.OrderNumber && item.InformationRequestId == irOrderLinkVO.InformationRequestId).Max(item => item.Id);

我像下面同样解决了

List<Entities.InformationRequestOrderLink> links = adjustmentContext.InformationRequestOrderLinks
.Where(item => item.OrderNumber == irOrderLinkVO.OrderNumber && item.InformationRequestId == irOrderLinkVO.InformationRequestId).ToList();

int id = 0;

if (links.Any())
{
  id = links.Max(x => x.Id);
 }
if (id == 0)
{
//do something here
}

---

#4楼

除了Ladislav Mrnka的答案：

若是要在“设置”选项卡上发布和覆盖容器，则能够将MultipleActiveResultSet设置为True。 您能够经过单击“ 高级...”找到此选项，它将位于“ 高级”组下。

---

#5楼

这是须要参考的人的有效链接字符串。

<connectionStrings>
    <add name="IdentityConnection" connectionString="Data Source=(LocalDb)\v11.0;AttachDbFilename=|DataDirectory|\IdentityDb.mdf;Integrated Security=True;MultipleActiveResultSets=true;" providerName="System.Data.SqlClient" />
  </connectionStrings>