如何使用实体框架从SQL表中获取两个列值的总和？

Question

I have a table name GRNDtlReturn in above mention screenshot. I want to get the sum of ReturnQuantity of first and third rows in table. I have written some code, but it returns the sum of full ReturnQuantity column. Please help me to solve this.

Here's my code:

public IList<GRNDtlReturnModel> GetReturnSum()
{
    return igrndtlreturnRepository.GetList (x=> x.GRNNo == "GRN00022"  && x.ProductCode == "D/F/HL/DM/0003/C/002")
            .Select(y => new GRNDtlReturnModel
            {
                GRNNo = y.GRNNo,
                totalQuantity = context.GRNDtlReturns.Sum(p => p.ReturnQuantity)
            }).ToList();
} 

Answer 1

public IList<GRNDtlReturnModel> GetReturnSum()
{
        return igrndtlreturnRepository.GetList(x=> x.GRNNo == "GRN00022" && 
                                                x.ProductCode == "D/F/HL/DM/0003/C/002")
            .Select(y => new GRNDtlReturnModel
            {
                GRNNo = y.GRNNo,

                totalQuantity = context.GRNDtlReturns.
                                Where(t=> t.GRNNo==y.GRNNo).Sum(p => p.ReturnQuantity)

            }).ToList();
}

Answer 2

I assume that igrndtlreturnRepository.GetList(x => x.GRNNo == grnno && x.ProductCode == productcode) returns an IQueryable<GRNDtlReturn> according to the filter expression.

Case 1: Get a single result for GRNNo = "GRN00022" and ProductCode = "D/F/HL/DM/0003/C/002"

In this case, the result of GetList is already limited to the relevant entries and there should be a single result GRNDtlReturnModel if any row matches the criteria.

GRNDtlReturnModel result = igrndtlreturnRepository.GetList(x => x.GRNNo == "GRN00022" && x.ProductCode == "D/F/HL/DM/0003/C/002")
    .GroupBy(x => x.GRNNo, (k, v) => new GRNDtlReturnModel { GRNNo = k, totalQuantity = v.Sum(q => q.ReturnQuantity) })
    .FirstOrDefault();

Case 2: Get the group-sum for all matching combinations of GRNNo and ProductCode

In this case, the grouping expression needs to contain all relevant group keys, the calculation of sum stays the same.

IList<GRNDtlReturnModel> result = igrndtlreturnRepository.GetList(x => true)
    .GroupBy(x => new { x.GRNNo, x.ProductCode }, (k, v) => new GRNDtlReturnModel { GRNNo = k.GRNNo, totalQuantity = v.Sum(q => q.ReturnQuantity) })
    .ToList();

This should be more efficient than a nested access to context.GRNDtlReturns .