Fetching data from cache if available, fetch from database if not - asp.net

Question

I have a page that need to run a query against a large dataset very often. To ease the burden on the database, I've set up a cache that will refresh itself every 5 minutes.
The logic is:
When a call is made, check if there is data in cache, if it is, run the queryu on the cache. If not, start a task of fetching from all rows from database while running a query on my repository to get out just the data needed for that call. When all rows is fetched, put it in the cache so it can be accessed on the next call. The problem is that I sometimes get a: "Message = "There is already an open DataReader associated with this Command which must be closed first." I guess this is because it runs two queries to the same repository at the same time (one for all rows and one for the query). I've got MARS enabled in my connections string.
My code
public IQueryable<TrackDto> TrackDtos([FromUri] int[] Ids)
{
if (HttpContext.Current.Cache["Tracks"] != null && ((IQueryable<TrackDto>)HttpContext.Current.Cache["Tracks"]).Any())
{
var trackDtos = Ids.Length > 0
? ((IQueryable<TrackDto>)HttpContext.Current.Cache["Tracks"]).Where(trackDto => Ids.Contains(trackDto.Id).AsQueryable()
: ((IQueryable<TrackDto>)HttpContext.Current.Cache["Tracks"]).AsQueryable();
return trackDtos;
}
else
{
UpdateTrackDtoCache(DateTime.Today);
var trackDtos = Ids.Length > 0
? WebRepository.TrackDtos.Where(trackDto => trackDto.Date == DateTime.Today && Ids.Contains(trackDto.Id)).AsQueryable()
: WebRepository.TrackDtos.Where(trackDto => trackDto.Date == DateTime.Today).AsQueryable().AsQueryable();
return trackDtos;
}
}
private IQueryable<TrackDto> MapTrackDtosFromDb(DateTime date)
{
return WebRepository.TrackDtos.Where(tdto => tdto.Date == date.Date);
}
private void UpdateTrackDtoCache(DateTime date)
{
if (CacheIsUpdating)
return;
CacheIsUpdating = true;
var task = Task.Factory.StartNew(
state =>
{
var context = (HttpContext)state;
context.Cache.Insert("Tracks", MapTrackDtosFromDb(date), null, Cache.NoAbsoluteExpiration,
new TimeSpan(0, 5, 0));
CacheIsUpdating = false;
},
HttpContext.Current);
}

Answer 1

I believe you are running DML or DDL sql queries using the same active connection. And MARS does not allow that. You can execute multiple select statements or bulk insert but if you run multiple update, delete statements or your sql execution will throw this kind of errors. Even if you run an update sql query while running a select statement on the same command you will get this error. For more info read this
http://msdn.microsoft.com/en-us/library/h32h3abf(v=vs.110).aspx