How to select name corresponding the id using LINQ

Question

I have a class points.cs which has members :

  public class Points
    {
        public int Id = 0;
        public string Name { get; set; }
    }


I have a list of these points like this `List<Points> list= new List<Points>();`

Now this list object contains data:

list:

 Id    Name
  1    abc
  2    def
  3    ghi
  4    jkl

What i have to do is to get the Name corresponding to the id number providing in my code using LINQ query from list object.

My try which os obviously wrong is:

 string nameFetchedId=list.Select(Name).Where(obj=>obj.Id=2) //result returned will be "def"

Please correct me, I am not good in LINQ ?

@Lepijohnny: Correct. And there are a variety of ways to handle that, depending on what that means to the business logic being invoked. Which is outside the scope of the question. — David, Dec 26 '16 at 13:35

score 6 · Answer 1 · answered Dec 26 '16 at 13:28

6

Your query needs to be:

string name = list.SingleOrDefault(obj => obj.Id == 2)?.Name; // ?. will prevent the code from throwing a null-reference exception and will return null when a point with Id = 2 does not exist

answered Dec 26 '16 at 13:28

George Findulov

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16

Masoud Andalibi · Accepted Answer · 2016-12-26T13:33:26.543

2

Greetings you may want to go like this using lambda expression:

string strName = list.where( x => x.id == 2).SingleOrDefault()?.Name;

Goodluck

edited Dec 26 '16 at 13:33

answered Dec 26 '16 at 13:27

Masoud Andalibi

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2

Be careful about null reference. – Johnny Dec 26 '16 at 13:32

MacakM · Answer 3 · 2016-12-26T13:33:10.733

0

It should be

string nameFetchedId=list.SingleOrDefault(obj=>obj.Id==2)?.Name;

First you find your object, then select its Name :)

edited Dec 26 '16 at 13:33

answered Dec 26 '16 at 13:27

MacakM

1,804
3
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score 0 · Answer 4 · edited May 23 '17 at 11:53

Selects first that meats the condition return null if not found

list.SingleOrDefault(obj=>obj.Id == 2); 
list.FirstOrDefault(obj=>obj.Id == 2);

in c# 6 use so you don't have to check if item is found

list.SingleOrDefault(obj=>obj.Id == 2)?.Name; 
list.FirstOrDefault(obj=>obj.Id == 2)?.Name;

this will return null or the Name value.

Selects first that meats the condition throws exception if not found

list.Single(obj=>obj.Id == 2);
list.First(obj=>obj.Id == 2);

with this it's safe to use list.Single(obj=>obj.Id == 2).Name; list.First(obj=>obj.Id == 2).Name; You will not get null unless the Name is null just an exception.

If you are using some sort of LINQ to data server (EF,NH,Mongo) some solutions will act a bit differently then when doing in memory query For more info on Single vs First check out LINQ Single vs First

How to select name corresponding the id using LINQ

4 Answers4