FirstOrDefault（）返回字符串的第一个字母

Question

I've a people object

        people.Add(new Person { FirstName = "Tim", Id = 1, LastName = "Corey" });
        people.Add(new Person { FirstName = "Sue", Id = 2, LastName = "Storm" });
        people.Add(new Person { FirstName = "Bilbo", Id = 3, LastName = "Baggins" });

I'm trying to query it by passing FirstName and LastName (Tim, Corey)

return people.Where(names => names.FirstName == FirstName && names.LastName == LastName).FirstOrDefault().FirstName;

This returns output as

"Tim"

When I added .FirstOrDefault() at the end. It brought strange output as

return people.Where(names => names.FirstName == FirstName && names.LastName == LastName).FirstOrDefault().FirstName.FirstOrDefault();

84 'T'

Could anyone explain how did the output produced.

84 'T'

Answer 1

You are calling .FirstOrDefault() on FirstName which is a string . This will cause the .FirstOrDefault() to be called on the IEnumberable<char> implementation. This will result in returning the first or default character in that string .

The numeric value 84 is displaying the ASCII value for T . http://www.rapidtables.com/code/text/ascii-table.html

Answer 2

Strings are arrays of characters, which can be enumerated by Linq.

FirstOrDefault returns the first item in the list, or null.
In this case, the first character in the array ['T', 'i', 'm'] is 'T'.

I think this is what you meant to write:

return people.First(names => names.FirstName == FirstName && names.LastName == LastName).FirstName;

Note: Using FirstOrDefault can return null, which would cause a NullReferenceException if there are no matches.

Alternatively:

var match = people.FirstOrDefault(n => n.FirstName == FirstName && n.LastName == LastName);
return (match == null) ? "" : match.FirstName;

Answer 3

是的- string本质上是IEnumerable<char>因此，当您调用FirstOrDefault() ，您将返回IEnumerable的第一个char 。