Question

Down Below I took part of a code I was looking at. I don’t understand the IEnumerable part of the Code. Can someone just walk me through the meaning of each line. Thanks

I don’t understand the Where(u =>) more than the rest.

  public static List<AAlexUsers.Models.SearchClass> Users(string userId, string email, string lastFourdigits)   
    {
        SearchClass Alex = new SearchClass();
        Alex.userId = "1234";
        Alex.email = "[e-mail]";
        Alex.lastFourdigits = "1885";

        SearchClass Emilio = new SearchClass();
        Emilio.userId = "0928";
        Emilio.email = "[e-mail]";
        Emilio.lastFourdigits = "0706";

        SearchClass Ulysses = new SearchClass();
        Ulysses.userId = "0914";
        Ulysses.email = "[e-mail]";
        Ulysses.lastFourdigits = "01zx";

        var list = new List<SearchClass>();
        list.Add(Alex);
        list.Add(Emilio);
        list.Add(Ulysses);

        IEnumerable<SearchClass> result = list;
         if (!string.IsNullOrEmpty(userId))
            result = result.Where(u => u.userId == userId);
        if (!string.IsNullOrEmpty(email))
            result = result.Where(u => u.email == email);
        if (!string.IsNullOrEmpty(lastFourdigits))
            result = result.Where(u => u.lastFourdigits == lastFourdigits);


        return list.ToList();

    }

Answer 1

The IEnumerable is a collection of SearchClass objects. See it as something like a list or an array.

IEnumerable is a generic interface describing something that can be enumerated (you can iterate through it and see/retrieve all of its elements). The content of this IEnumerable can have been pre-generated, or is live/lazily generated when you try to iterate through ‘result’ (IEnumerable).

The next lines are queries run against this “result’ list:

result = result.Where(u => u.userId == userId);

can be confusing since it assigns the return of the query to the data the query is run on.
Let’s take a simpler example:

var myResult= myEnumerableList.Where(u => u.userId == "Yusuf");

means that “var myResult” contains all elements from myEnumerableList, only when this element (here, called ‘u’)has a property userId that is equal to “Yusuf”

.Net provides powerful ways to query collections/lists/anything_enumerable, presented with an SQL-like syntax