C＃代码/表达式以查找某个值在-的范围内

Question

I will just explain in brief what I have.

I have a list of configuration data like this --

Now I am trying to write code to find out which set/config a certain user falls, based upon his purchase sales amount. for eg. if he has made a sale of 23000 bucks he becomes a G01 grade salesguy. If he made 51000 bucks, he is G04 grade. If he made sale of 29000 bucks he would be G02 grade. Or if he made 71000 he is obviously G05 grade. Like that. To explain my use-case.

The code/logic I wrote was something like -

public JsonResult CustomerGradeByID([FromBody]decimal saleAmt)
{
    try
    {
        var cGrade = CustomerGrade(Convert.ToDecimal(saleAmt));
        return Json(cGrade);
    }
    catch (Exception exp)
    {
        return Json(exp.GetBaseException());
    }
}
protected string CustomerGrade(decimal salesTot)
{
    try
    {
        var grades = _appDbContext.CustomerGrades.ToList();
        CustomerGrade cg = grades.Aggregate((a, b) => a.grade_minsaleamount < salesTot && salesTot < b.grade_minsaleamount ? a : b);
        var gdName = cg.grade_name.ToString();
        return gdName;
    }
    catch(Exception exp)
    {
        throw exp;
    }
}

Don't worry about _appdbcontext and all that I am just fetching and populating from my db where that table is stored. Apparently the logic for 'CustomerGrade' is wrong. Because it is giving me all kinds of haywire results. For 33000 bucks sale it gives G01, for 61000 bucks it gives G04 and similar other all kinds of erroneous outputs. I tried using lambda aggregate. But seems it is incorrect.

Can you help me perfect this logic please? A bulletproof logic for this scenario? It would be hugely helpful for me! Thanks to all,

This is my actual set of data --

Answer 1

Assuming grade_minsaleamount are unique, you can just order the list and use FirstOrDefault i guess, it can all be done on the DB

var result = _appDbContext.CustomerGrades
                          .OrderBy(x => x.grade_minsaleamount)
                          .FirstOrDefault(x => salesTot >= x.grade_minsaleamount);

// Sanity check for null
if(result != null)
{
   // found!
   Debug.WriteLine(result.Name);
}

---

Additional Resources

Enumerable.FirstOrDefault Method

Returns the first element of a sequence, or a default value if no element is found.

Enumerable.OrderBy Method

Sorts the elements of a sequence in ascending order.

Update

_appDbContext.OrderBy(x => x.MinSaleAmount)
                      .LastOrDefault(x => x.MinSaleAmount < salesTot);

Ok what this is saying is

Order the sales amount like you have in your table. Filter out anything above that sales amount, and choose the last one.

If salesTot is higher then the last items in the list, it will return the last item in the list. if it is less than the minimum it will return null.

The confusion here was basically the concept if minimum sales amount, to be a G02 they cannot make less than 25000, or they are G01. However there is no upper limit. Though there is a finite lower limit