The result of a query cannot be enumerated more than once. even I user ToList.

Gaurang Thakkar 1

I get following error on EF6 when trying to go over list for different output.
I have read that we have to use ToList to solve this. But in my case, even if I user new variable at each stage, I am getting same error.

below is sample code for the same
var branchList = (
from br in db.BranchTbls
join ct in db.CityTbls on br.CityID equals ct.CityID
into ctLeft
from ctL in ctLeft.DefaultIfEmpty()

                where br.IsActive == true
                select new
                {
                    br.BranchID,
                    br.BranchName,
                    ctL.CityName,
                }
            ).ToList();
            var lrdetailsTemp1 = branchList
                .Select(o =>
                    new
                    {
                        detail = o,
                        lrs = db.SP_GetPendingLoadLR(0, 0, (int)o.BranchID)
                    }
                ).ToList();
            var lsdetailsTemp2 = lrdetailsTemp1
            .Select(o =>
                new
                {
                    o.detail.BranchID,
                    o.detail.BranchName,
                    o.detail.CityName,
                    Cnt = o.lrs.Count(),
                    TotGrWt = o.lrs.Sum(x => x.GrossWt)
                }
                ).ToList()
            .Where(o => o.Cnt > 0)
            .OrderBy(o => o.CityName)
            .ThenBy(o => o.BranchName)
            .ToList();

Daniel Zhang-MSFT 9,621 Reputation points

2021-01-29T08:11:06.247+00:00
Hi @Gaurang Thakkar ,
Have you checked if none of the three lists( branchList,lrdetailsTemp1,lsdetailsTemp2 )can be enumerated more than once?
And I suggest you use Enumerable.Any method to determine whether a list contains any elements first.

If(list.Any()) { //check if it contains any elements }

Best Regards,
Daniel Zhang
Gaurang Thakkar 1 Reputation point

2021-01-29T10:02:23.817+00:00

Hi Daniel,

initially, it was single query (long). But even after putting ToList on each part, I was not able to over come the issue.
Then I introduce different variables, hoping if that solves the issue, but it was the same.
at last the error was showing when I try to populate variable "lsdetailsTemp2".

right now, I have created a private class and getting primary result into the list of that class.
and looping throgh that list to fetch and fill other data.

To answer your question to see if list contain any list - Yes it is.

Below is the code with private class.
(limit exceed when I put code., So I am addint that in parts)

Gaurang Thakkar 1

var branchList = (
                        from br in db.BranchTbls
                        join ct in db.CityTbls on br.CityID equals ct.CityID
                        into ctLeft
                        from ctL in ctLeft.DefaultIfEmpty()

                        where br.IsActive == true
                        select new PendingDispatch()
                        {
                            BranchId = br.BranchID,
                            BranchName = br.BranchName,
                            BranchCity = ctL.CityName
                        }
                    ).ToList();


                foreach (var br in branchList)
                {
                    var lrs = db.SP_GetPendingLoadLR(0, 0, (int) br.BranchId).ToList();
                    br.LrCount = lrs.Count();
                    br.GrossWt = lrs.Sum(x => x.GrossWt);
                }

Gaurang Thakkar 1 Reputation point

2021-01-29T10:04:51.047+00:00

branchList = branchList.Where(o => o.LrCount > 0)
.OrderBy(o => o.BranchCity)
.ThenBy(o => o.BranchName)
.ToList();
Daniel Zhang-MSFT 9,621 Reputation points

2021-02-01T09:05:30.887+00:00

Hi @Gaurang Thakkar ,
>>at last the error was showing when I try to populate variable "lsdetailsTemp2".
According to my understanding, your branchList and lrdetailsTemp1 lists can be successfully enumerated.
The problem is in your lsdetailsTemp2 list. If not, please correct me.
And does your "lsdetailsTemp2" list contain elements? And what is the specific error message?
Best Regards,
Daniel Zhang
Gaurang Thakkar 1 Reputation point

2021-02-03T04:09:49.98+00:00

Hi Daniel,

does your "lsdetailsTemp2" list contain elements? - Yes.

I had change the code as I shown earlier. And move that to production.
For now we can close this question. I will get back to you (or open a new question) in future if I encounter similar issue.

Thanks for your time.

Regards,
Gaurang

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The result of a query cannot be enumerated more than once. even I user ToList.