Emulating SQL IN statement using Linq

FilterDictionary.cs

var needles = new List<string> { "b", "d" };

var haystack = new Dictionary<string, object>
{
    { "a", 1 },
    { "b", 2 },
    { "c", false },
    { "d", "test" }
};

Console.WriteLine("Imperatively filtered:");
foreach (var p in FilterService.ImperativelyFiltered(needles, haystack))
{
    Console.WriteLine($"{p.Value}");
}
Console.WriteLine();

Console.WriteLine("Delcaratively filtered:");
foreach (var p in FilterService.DeclarativelyFiltered(needles, haystack))
{
    Console.WriteLine($"{p.Value}");
}
Console.WriteLine();

static class FilterService
{
    public static IDictionary<string, object> ImperativelyFiltered(
            IList<string> needles,
            IDictionary<string, object> haystack)
    {
        var filtered = new Dictionary<string, object>();
        foreach (var needle in needles)
        {
            if (haystack.ContainsKey(needle))
            {
                filtered.Add(needle, haystack[needle]);
            }
        }
        return filtered;
    }

    public static IDictionary<string, object> DeclarativelyFiltered(
            IList<string> needles,
            IDictionary<string, object> haystack) =>
        haystack.Where(p => needles.Contains(p.Key)).ToDictionary(p => p.Key, p => p.Value);

}