LINQ: Select an object, but change some properties without creating a new object

Q: Using LINQ, if I wanted to perform some query and return the object from the query, but change only some of the properties in that object, how would I do this without creating a new object and manually set every property? Is this possible?

Example

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

This post is based off of my Stack Overflow questionon the same topic.

You can do it via the LINQ extension methods pretty easily, as JaredPar answered:

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

But what if you wanted to use declarative syntax similar to my above example?  You could write a simple extension method to do that (code is below).

Usage

// select some monkeys and modify a property in the select statement
// instead of creating a new monkey and manually setting all properties
var list = from monkey in monkeys
select monkey.Set(monkey1 =>
{
    monkey1.FavoriteFood += " and banannas";
});

This is much quicker and more concise than creating a new monkey object and manually setting all properties, like so:

Ugly code

// instead of this ugly code:
var list = from monkey in monkeys
select new Monkey {
    Name = monkey.Name,
    FavoriteFood = monkey.FavoriteFood += ” and banannas”,
    FavoriteBeer = monkey.FavoriteBeer,
    FavoriteActivity = monkey.FavoriteActivity,
    EyeColor = monkey.EyeColor,
    HairColor = monkey.HairColor,
    LikesToFlingPoo = monkey.LikesToFlingPoo
// etc… };

A: Write an extension method.  I wrote an extension method called Set that to facilitate this.  All it does is allow you to write a lambda expression inside your select statement that returns the same object that you pass it.  You can set any number of properties on that object without creating a new instance of it.  Here’s the source code:

Extension Method Code

• Source hosted at my Helpers.Net GitHub Project

/// 
/// Used to modify properties of an object returned from a LINQ query
/// 
public static TSource Set(this TSource input, Action updater)
{
    updater(input);
    return input;
}

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