如何在 LINQ 和 C# 中使用 if 条件

Question

I want to display value of one variable whose value depend on another variable. let say if I have three rows in a table:

starttime   endtime  comment
02:55       15:56    abc
03:54       23:46    def
09:33       12:69    oiuy

I want to use Where condition in Linq such that comment should be display on the basis of starttime, so that if I select 02:55 , then comment should display abc .

i use this linq query:

Comment = fr.Where(x => x.Starttime).Comment

but it is not correct. Can anyone suggest what improvement I need?

Answer 1

The Where clause must return a bool , so all you're missing is the actual comparison:

fr.Where(x => x.Starttime == "02:55")

But now we also need to decide what to select. There may be many, one, or no items returned. If we only want the first match, we can use FirstOrDefault , which will return the first record, or null if none are returned. We can also select a default value, like "[no match found]" if no records are returned, by comparing the result of FirstOrDefault to null (using the ?? operator):

var comment = fr
    .Where(item => item.Starttime == "02:55")
    .FirstOrDefault()
    ?.Comment ?? "[no match]";

If we want to select many comments, then we can use the Select method to specify the property we want to select, and ToList() to return them all in a List<string> :

var allComments = fr
    .Where(item => item.Starttime == "02:55")
    .Select(item => item.Comment)
    .ToList();

---

Update

Now that you've posted a screenshot of your code (which is not recommended here - better to paste the relevant code into a code section in your question), it appears that you're setting properties of an instance of an anonymouse type based on the properties of items in an IGrouping .

Since you have StartTime = fr.Min(x => x.StartTime) , and apparently the Comment is somehow related to StartTime , you may want to do something like this:

// Get the Comment from the item with the smallest (Min) StartTime
Comment = fr.OrderBy(x => x.StartTime).FirstOrDefault()?.Comment ?? "[no comment]",

Answer 2

Try

var comments = fr.Where(x => x.Starttime == val).Select(x=> x.Comment);

If you only want the first match, try

 var comment = fr.Where(x => x.Starttime == val).FirstOrDefault()?.Comment;

or more concisely

var comment = fr.FirstOrDefault(x => x.Starttime == val)?.Comment;