Grouping data using entity framework

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WPF

entity-framework

C#7.0

I have table contain some fields like (EmployeeId + OperationId + Operation_Amount)

I want to get the summation of Operation_Amount for every operation to every employee

Result will be as (EmployeeId + OperationId + Sum_Of_Operation_Amount)

I try use grouping , but I found some rows repeated , then try to use Distinct keyword but also fail

can some one help me pls ...

Imgur: The magic of the Internet[^]

Imgur: The magic of the Internet[^]

Imgur: The magic of the Internet[^]

What I have tried:

var sr = source
    .GroupBy(x => x.OperationId)
    .Distinct()
    .SelectMany(v => v.Distinct())
    .Select(n => new VoucherForPrintSalaryInvoice()
    {
        EmployeeName = n.Employee.EmployeeName,
        OperationName = n.Operation.OperationName.ToString(),
        OperationTypeId = n.Operation.OperationTypeId,
        Amount = _voucherService
            .GeSumOftEmployeeOperations(n.EmployeeId, App.MainCurrency, App.MainCurrency, month, year)

    })
    .Distinct()
    .ToList();