Is there a C# IN operator?

linq

extension-methods

null-handling

byAnton Shumikhin·Oct 20, 2024

C# uses the Contains method on collections like arrays or lists to replicate the functionality of the SQL IN operator. It checks whether an element resides within the collection. Check this:

int[] numbers = { 1, 3, 5, 7 };
int target = 3;

bool exists = numbers.Contains(target); // Reminds me of my mom hunting for Easter eggs

Here, numbers.Contains(target) acts as the SQL IN operation, checking whether target is 'IN' numbers.

Crafting "IN" with extension methods

Extension methods can provide a cleaner look when frequently checking existence in an array or a list. They act as the SQL IN operator making your code more elegant:

public static class LinqExtensions
{
    public static bool In<T>(this T source, params T[] list)
    {
        if (list == null)
            throw new ArgumentNullException("Space is vast, but null arguments are not welcomed!"); // Some humor right there

        return list.Contains(source);
    }
}

I can use it now:

if (target.In(1, 3, 5, 7))
{
    // Print: I knew you were there!
}

The use of params keyword allows providing multiple arguments, so no need for an array here.

Embrace the might of LINQ

C# provides Language-Integrated Query (LINQ) that packs a punch even with no native 'IN' operator. The functions Where and Any come to the rescue:

var isAvailable = products.Any(p => desiredIds.Contains(p.Id)); // Is my dream gadget in the list?

The above line uses LINQ's Any to seek if any product's ID is within the desiredIds list, much like SQL's IN.

Diverse data types with "IN" functionality

The 'IN' logic can be applied to even ranges and various data types. Imagine checking if a string, date, or even custom types are 'IN' a collection:

if ("banana".In("apple", "banana", "cherry"))
{
    // Banana found, not slipped! Debug with caution.
}

Graceful handling of nulls

Null inputs need to be handled with care to avoid any exceptions. Add null checks within your In extension method:

public static bool SafeIn<T>(this T source, params T[] list)
{
    return list?.Contains(source) ?? false; // Nulls are shifty, tackled it now!
}

Better the Enumerable, sweeter the code

Patterns like SQL IN can be effectively translated into C# using the mighty Enumerable methods:

// Verify if any player has reached one of several milestone scores
var milestoneScores = new int[] { 100, 200, 300 };
bool hasMilestoneReached = players.Any(player => milestoneScores.Contains(player.Score));