At least one object must implement icomparable. LINQ C#

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Dear All,

I have a List and i'm appling GroupBy, Orderby & ThenBy using LINQ-C#.

When i change the requestDate and remarks i'm getting the following erro.

At least one object must implement IComparable.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.ArgumentException: At least one object must implement IComparable.

What I have tried:

C#

IEnumerable<CandidateRefundVoucherInfo> requestVouchers = CandidateRefundVoucherController.Instance.GetByCenterID(16);

            if (requestVouchers.Count() > 0)
            {
                var CandidateRefundVouchers = requestVouchers.
                    Select(items => new
                    {
                        CertificateID = items.Certificate.ID,
                        items.Certificate.Code,
                        items.Certificate.NameEN,
                        items.Certificate.NameAR,
                        items.Remarks,
                        items.RequestDate,
                        items.NumberOfRefundVoucherRequest,
                        items.StatusType,
                        UpdatedByUser = items.UpdatedByUser.NameEN
                    }).
                    GroupBy(i => new
                    {
                        i.CertificateID,
                        i.Code,
                        i.NameEN,
                        i.NameAR,
                        i.Remarks,
                        i.RequestDate,
                        i.NumberOfRefundVoucherRequest,
                        i.StatusType,
                        i.UpdatedByUser
                    })
                        .OrderByDescending(d => new { d.Key.RequestDate })
                        .ThenBy(l => new { l.Key.Remarks })
                        .Select(item => new
                        {
                            ID = item.Key.CertificateID,
                            Code = item.Key.Code,
                            NameEN = item.Key.NameEN,
                            NameAR = item.Key.NameAR,
                            RequestedVouchers = item.Sum(items => items.NumberOfRefundVoucherRequest),
                            Status = item.Key.StatusType,
                            RequestedDate = item.Key.RequestDate.ToString("dddd, dd MMMM yyyy"),
                            Remarks = item.Key.Remarks,
                            UpdatedBy = item.Key.UpdatedByUser,
                            BindLink = BindCode(item.Key.CertificateID, item.Key.Code)
                        });

                rptCandidateRefundVouchers.DataSource = CandidateRefundVouchers;
                rptCandidateRefundVouchers.DataBind();

Can anyone please help me.

Thanks

Posted 22-Nov-18 3:01am

abdul subhan mohammed

Updated 23-Nov-18 9:04am

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Aydin Homay · Answer 1 · 2018-11-22T03:25:00

The error message is very clear, to order a set of things, there must be a way to compare two things. You need to implement IComparable interface, to provide compare versus another instance. In the case of your code problem, will occurs at OrderByDescending method.

See the below link as well:
c# - At least one object must implement IComparable calling OrderBy() - Stack Overflow[^]

abdul subhan mohammed · Answer 2 · 2018-11-23T09:05:00

I got it!

C#

IEnumerable<CandidateRefundVoucherInfo> candidateRefundVoucherList = requestVouchers;
                var refundVouchers = candidateRefundVoucherList.OrderByDescending(d => d.RequestDate).
                    GroupBy(r => r.RequestDate).Select(item => new {
                    ID = item.First().Certificate.ID,
                    Code = item.First().Certificate.Code,
                    NameEN = item.First().Certificate.NameEN,
                    NameAR = item.First().Certificate.NameAR,
                    RequestedVouchers = item.Sum(items => items.NumberOfRefundVoucherRequest),
                    Status = item.First().StatusType,
                    RequestedDate = item.First().RequestDate.ToString("dddd, dd MMMM yyyy"),
                    Remarks = item.First().Remarks,
                    UpdatedBy = item.First().UpdatedByUser.NameEN,
                    BindLink = BindCode(item.First().Certificate.ID, item.First().Certificate.Code, item.First().RequestDate.ToShortDateString())
                });

                rptCandidateRefundVouchers.DataSource = refundVouchers;
                rptCandidateRefundVouchers.DataBind();

At least one object must implement icomparable. LINQ C#

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