Lambda Expression using OR operator

Question

I believe there is a better way to write this but I am experiencing a mental block.

int num = 0;

using(var db = new TestDB())
{
    num = db.Table.Where(x => x.FavoriteSport == "Baseball" &&
                             (x.FavoriteColor == "Green" || 
                              x.FavoriteColor == "Blue" || 
                              x.FavoriteColor == "Red")).Count();
}

return num;

Is there a better way to write the OR statements? I have tried:

x.FavoriteColor == "Green" || "Blue" || "Red"

but the compiler says Operator || cannot be applied to operands of type 'bool' and 'string'

Any help is appreciated.

Answer 1

You can use Contains method of array/list/hashset.

var colors = new List<string> {"Green", "Red", "Blue" };

db.Table.Where(x => x.FavoriteSport == "Baseball" &&
                         (colors.Contains (x.FavoriteColor)).Count()

It will generate SQL query like

SELECT ... WHERE FavoriteColor = 'Baseball' AND FavoriteColor in ("Green", "Red", "Blue")

I'd like to add that if you work with datasets which are stored in a memory you should bear in mind that List's Contains takes O(N) iteration to get result. So if colors contains a lot of elements you should use set HashSet instead with O(1).

var colors = new HashSet<string> {"Green", "Red", "Blue", .... };

someDataSet.Where(x => x.FavoriteSport == "Baseball" &&
                         (colors.Contains (x.FavoriteColor)).Count()

You can find List-HashSet performance comparison here

Answer 2

string[] FavColor = new string[]{"Green","Red","Blue"};

int num = 0;

    using(var db = new TestDB())
    {
        num = db.Table.Where(x => x.FavoriteSport == "Baseball" &&FavColor.Any(x.FavoriteSport)).Count();
    }

    return num;