There is already an open DataReader associated wit

Question

I have this query and I get the error in this function:

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();
}

Error is:

There is already an open DataReader associated with this Command which must be closed first.

Update:

stack trace added:

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

Answer 1

I am using web service in my tool, where those service fetch the stored procedure. while more number of client tool fetches the web service, this problem arises. I have fixed by specifying the Synchronized attribute for those function fetches the stored procedure. now it is working fine, the error never showed up in my tool.

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

This attribute allows to process one request at a time. so this solves the Issue.

Answer 2

I donot know whether this is duplicate answer or not. If it is I am sorry. I just want to let the needy know how I solved my issue using ToList().

In my case I got same exception for below query.

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

I solved like below

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
}

Answer 3

I solved this problem by changing await _accountSessionDataModel.SaveChangesAsync(); to _accountSessionDataModel.SaveChanges(); in my Repository class.

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

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

Changed it to:

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

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

The problem was that I updated the Sessions in the frontend after creating a session (in code), but because SaveChangesAsync happens asynchronously, fetching the sessions caused this error because apparently the SaveChangesAsync operation was not yet ready.

Answer 4

For those finding this via Google;
I was getting this error because, as suggested by the error, I failed to close a SqlDataReader prior to creating another on the same SqlCommand, mistakenly assuming that it would be garbage collected when leaving the method it was created in.

I solved the issue by calling sqlDataReader.Close(); before creating the second reader.

Answer 5

In my case, I had opened a query from data context, like

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

... and then subsequently queried the same...

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

Adding the .ToList to the first resolved my issue. I think it makes sense to wrap this in a property like:

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

Where _stores is a private variable, and Filters is also a readonly property that reads from AppSettings.

Answer 6

Most likely this issue happens because of "lazy loading" feature of Entity Framework. Usually, unless explicitly required during initial fetch, all joined data (anything that stored in other database tables) is fetched only when required. In many cases that is a good thing, since it prevents from fetching unnecessary data and thus improve query performance (no joins) and saves bandwidth.

In the situation described in the question, initial fetch is performed, and during "select" phase missing lazy loading data is requested, additional queries are issued and then EF is complaining about "open DataReader".

Workaround proposed in the accepted answer will allow execution of these queries, and indeed the whole request will succeed.

However, if you will examine requests sent to the database, you will notice multiple requests - additional request for each missing (lazy loaded) data. This might be a performance killer.

A better approach is to tell to EF to preload all needed lazy loaded data during the initial query. This can be done using "Include" statement:

using System.Data.Entity;

query = query.Include(a => a.LazyLoadedProperty);

This way, all needed joins will be performed and all needed data will be returned as a single query. The issue described in the question will be solved.