Returning the result from a linq query but with one value modified

Question

I have a class like this

public class Product
{
    public int Id {get;set;}
    public string Name {get;set;}
    public Category Category {get;set;}
}

Now I want to query a List with Linq

var result = from p in products
             select p;

What I want to achive is that the result will set a default Category if it is empty.

What I can do is this

var result = from p in products
             select new Product()
             {
                 Id = p.Id,
                 Name = p.Name,
                 Category = p.Category ?? new Category() 
             }

but that requires me to set every field again. But that is not what I want because my real world entity has about 50 properties not 3 and I also have to renember to edit the code If I add another property in the future. What I am thinking is something more like this:

var result = from p in products
             select p { Category = p.Category ?? new Category() };

but that does not compile.

like I would do while constructing a product:

var product = new Product() { Category = new Category() };

I know I could just do this:

foreach (var p in result)
{
    if(p.Category == null)
        p.Category = new Category();
}

but I am passing the result to the caller an I don't want to itterate through my products at this moment.

Why aren't the properties initialized in the first place? If a product should have at least a category initialized with the default constructor, initialize the backing field accordingly. — Tim Schmelter
– Tim Schmelter, Commented May 24, 2013 at 10:33
If you're working with an ORM as datasource this may cause new Categories to be inadvertently inserted into the database. — Gert Arnold
– Gert Arnold, Commented May 24, 2013 at 13:32
That won't happen. Currently I am using the select new Product... approach and reassign every property. With the disadvantage that I have to modify the code everytime I add another property to my class. This is dangerous. I will never store the result, and even if I would try, my model has a [MinLength(5)] dataannotation on category.name, so it would fail anyway. — Jürgen Steinblock
– Jürgen Steinblock, Commented May 28, 2013 at 12:05

Eoin Campbell · Accepted Answer · 2013-05-24 10:37:22Z

2

I wouldn't recommend doing this in Linq. You're mixing business logic ( null values should be default initialized) with DataAcess code (get me products).

Can you not change your product class itself. Modify the "Category" property to something like.

private Category _category

public Category Category 
{
    get 
    {
        if (_category == null)
            _category = new Category();

        return _category;
    }
    set
    {
        _category = value;
    }
}

answered May 24, 2013 at 10:37

Eoin Campbell

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