LINQ: Select an object and modify its properties without having to create a new one.

Problem

I’d like to alter several properties of a LINQ query result object without having to create a new object and set each property manually. Is that even possible?

Example:

var list = from something in someList
           select x // but change one property

Asked by Rob Volk

Solution #1

I’m not sure how to write a query. However, here is a more detailed LINQ expression example.

var query = someList.Select(x => { x.SomeProp = "foo"; return x; })

This replaces an expression with an anonymous method. This allows you to combine many statements into a single lambda. As a result, you can use this method to combine the two procedures of setting the property and returning the object.

Answered by JaredPar

Solution #2

If all you want to do is update the property on all elements, this is the way to go.

someList.All(x => { x.SomeProp = "foo"; return true; })

Answered by Jon Spokes

Solution #3

This is the one I favor. It’s possible to use it in conjunction with other Linq instructions.

from item in list
let xyz = item.PropertyToChange = calcValue()
select item

Answered by Jan Zahradník

Solution #4

You shouldn’t be able to do this because of any LINQ wizardry. If you utilize projection, you’ll get an anonymous type.

User u = UserCollection.FirstOrDefault(u => u.Id == 1);
u.FirstName = "Bob"

This will change the physical object as well as:

foreach (User u in UserCollection.Where(u => u.Id > 10)
{
    u.Property = SomeValue;
}

Answered by Joshua Belden

Solution #5

Language Integrated Query, not Language Integrated Update, is not achievable with normal query operators. However, you might be able to disguise your change via extension methods.

public static class UpdateExtension
{
    public static IEnumerable<Car> ChangeColorTo(
       this IEnumerable<Car> cars, Color color)
    {
       foreach (Car car in cars)
       {
          car.Color = color;
          yield return car;
       }
    }
}

You can now utilize it in the following manner.

cars.Where(car => car.Color == Color.Blue).ChangeColorTo(Color.Red);

Answered by Daniel Brückner

Post is based on https://stackoverflow.com/questions/807797/linq-select-an-object-and-change-some-properties-without-creating-a-new-object