LINQ Select n 列表 ASP.NET 核心

Question

I have this code:

foreach(var i in category.count)
{
    var getDifferentSerialNumberforEachLoop = _db.Category.Where(a => a.CategoryID == 
    categoryID).Select(i=>i.SerialNumber).FirstOrDefault();

 //Proceed to do something else with the first serial number value
  .....
 ///end of the first serial number being processed, do again n times (number of categry.count 
 times)
}

So you have a case where a CategoryID can have many SerialNumbers associated with it, Example:

CategoryID     SerialNumber
12345          0123445
12345          2345678
12345          0987654
12345          8756478
....           ......(n times)
                          

I want to loop through and get each of those serial number and save to the variable, 'getDifferentSerialNumberforEachLoop' process that separately and do it again for all serial numbers associated with that CategoryID. But at the moment I'm only getting the first SerialNumber say 0123445 of course this is because I'm using 'FirstOrDefault()' so even though the Select(i=>i.SerialNumber) value changes each time it loops through category.count the variable, getDifferentSerialNumberforEachLoop will always be the firstordefault value.

My question is: how do I make the getDifferentSerialNumberforEachLoop to always have the next SerialNumber value?

I can't use .Take(4) because I don't know if category.count will always be 4 - if that make sense?

Can't use LastOrDefault because I wouldn't get the first to the last values, I can't use List() because I only want one SerialNumber value at a time.

So is there a way I could go about this? I've also seen Takewhile but not sure about that? Any other query I could use for this please? Thank you.

Answer 1

I'd Suggest something like the below.

foreach(var i in category.count)
{
    var getDifferentSerialNumberforEachLoop = _db.Category.Where(a => a.CategoryID == 
    categoryID).Select(i=>i.SerialNumber).ToList().ForEach(serialNo => {
      Console.WriteLine(serialNo);
    });
}

You say you "cannot use List because you need one Serial Number at a time" but doing ToList() and ForEach will allow you to iterate over each Serial Number at a time.