Query and updating a property in a collection using LINQ

Question

What is the most succint/simple way of updating a single property of a specific item within a collection using LINQ?

For example if I have a List of the following:

public class Ticket
{
    public string Name { get; set; }
    public string Code { get; set; }
    public bool Selected { get; set; }
}

How can I use LINQ to update the "Selected" property of a Ticket item wheres its "Name" property has the value of "Beach". In SQL it would be:

UPDATE Tickets SET Selected = true WHERE Name = 'Beach'

I thought I was on the right track with this...

tickets.Select(x => { x.Selected = true; return x; }).ToList().Where(x => x.Name == "Beach");

score 32 · Accepted Answer · edited May 23 '17 at 12:01

32

You can change the order, then use the ForEach operator:

tickets
   .Where(x => x.Name == "Beach")
   .ToList()
   .ForEach(x => { x.Selected = true; });

Note:

that the ToList() is needed because IEnumerable doesn't support ForEach in Linq - see LINQ equivalent of foreach for IEnumerable<T>
that for readability it might be better to separate this out into a linq query and then a more conventional foreach(x in list) C# loop
if this is linq-to-sql, then you'll need to call SubmitChanges() in order to persist your changes.

edited May 23 '17 at 12:01

Community

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1

answered Mar 15 '11 at 20:16

Stuart

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Why ToList()? Sure it was in the OP, but it is probably unnecessary overhead. – Chris Shouts Mar 15 '11 at 20:19
The reason is - http://stackoverflow.com/questions/200574/linq-equivalent-of-foreach-for-ienumerablet – Stuart Mar 15 '11 at 20:19
`IEnumerable` doesn't support `.ForEach()`, so it's needed. – BrokenGlass Mar 15 '11 at 20:19
I prefer to your solution than the other one,because the code is more readable. Is there any performance advanatage for FloatLeft's suggestion ? – kbvishnu Sep 10 '13 at 14:09

score 8 · Answer 2 · edited Mar 17 '14 at 03:23

8

Bit late for an answer but i think we don't have to convert to ToList() as Mentioned by stuart what actually we can do is just tweak Stuart code(which is great piece of code) as following

tickets
   .Where(x => x.Name == "Beach")
   .All(x => x.Selected = true);

Another option

tickets
   .Where(x => x.Name == "Beach")
   .All(x => { x.Selected = true; return true; });

edited Mar 17 '14 at 03:23

Paresh Mayani

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answered Mar 17 '14 at 00:26

Atul Chaudhary

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score 1 · Answer 3 · answered Mar 15 '11 at 20:20

1

Let me start off by saying this, don't use LINQ to set properties like that, that's not how LINQ's meant to be used.

You should write the query to select the rows to be changed, change them in a loop, and submit the changes to the database (if LINQ to SQL).

var query = tickets.Where(ticket => ticket.Name == "Beach");
foreach (var item in query)
    item.Selected = true;

// if LINQ to SQL
context.SubmitChanges();

answered Mar 15 '11 at 20:20

Jeff Mercado

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Jeff, please can you supply a reason why you think LINQ should not be used in this way? The ForEach() is doing exactly the same thing as your foreach loop. – IsolatedStorage Sep 05 '13 at 05:03
1

@IsolatedStorage ForEach is not part of LINQ anyway... The reason is noone actually expects Where/Select/Any/All to update existing objects - as result doing so will cause confusion... Delayed execution does make it even more entertaining. – Alexei Levenkov Jan 29 '18 at 08:49

Query and updating a property in a collection using LINQ

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