LINQ 使用方法语法查询

Question

My requirement is to make boolean value (IsPC=true) only if I found any value with IsCurrent = true from the list and second condition is to filter the list with G or W codes and third condition is to check the PCBNumber length ==15 with only one from the list.

How short can i able to reduce the below query using LINQ method syntax below is my query

     var CurrentQ= p.List.Where(x => x.IsConCurrent== true);
            if (CurrentQ.Count() > 0)
            {
                var NCurrentQwithWorQ = p.List.Where(x => x.Codes == Codes.W|| x.Codes== Codes.Q).Count();
                if (NCurrentQwithWorQ  != null)
                {
                    var PCBNumber = p.List.Where(x => x.PCBNumber .Length == 15).Count();
                    if (PCBNumber == 1)
                    {
                        isPC = true;
                    }
                }
}

Answer 1

You can use all conditions in same query like below,

var PCBNumber= p.List.Where(x => x.IsConCurrent== true && (x.Codes == Codes.W|| x.Codes== Codes.Q) && x.PCBNumber.Length == 15);
if (PCBNumber !=null && PCBNumber.Count() == 1)
{
   isPC = true;
}

Answer 2

I'm not trying to debug what you wrote, but isn't this really what you're looking for--that is, daisy-chaining your Where conditions?

var isPC = p.List.Where(x => x.IsConCurrent == true).Where(x => x.Codes == Codes.W || x.Codes == Codes.Q).Where(x => x.PCBNumber.Length == 15).Count() == 1;

Answer 3

Both solutions suggested above are correct.

p.List.Where(x => x.IsConCurrent== true && (x.Codes == Codes.W|| x.Codes== Codes.Q) && x.PCBNumber.Length == 15);
p.List.Where(x => x.IsConCurrent == true).Where(x => x.Codes == Codes.W || x.Codes == Codes.Q).Where(x => x.PCBNumber.Length == 15).Count()

Actually they are performed in the same way. The Where function does not force immediate iteration through the data source. Only when you execute the Count function, LINQ will process row by row and execute criterion by criterion to find out which values should be calculated.

I can only suggest you add the Take(2) operator after the where clause. In this case LINQ will stop after finding the first two rows that matches provided criterion and other rows will not be processed.

p.List.Where(x => x.IsConCurrent == true)
   .Where(x => x.Codes == Codes.W || x.Codes == Codes.Q)
   .Where(x => x.PCBNumber.Length == 15)
   .Take(2).Count()