Question

I need to filter and order data entries after criteria that a user selects through a dropdown. Selectable will be things like “newest entries first”, “oldest entries first”, “lowest price first” etc.

I could just create an enum for the options and switch/case where I retrieve the data, but I’d rather do this in an easily extendable way.

What design pattern would fit the situation best?

Answer 1

Everyone has mentioned the strategy pattern. Just thought I’d post my simple implementation. No need to make it more complicated than necessary.

public enum SortMethod
{
    Newest,
    Oldest,
    LowestPrice,
}

public class Foo
{
    public DateTime Date {get;set;}
    public decimal Price {get;set;}
}


...
var strategyMap = new Dictionary<SortMethod, Func<IEnumerable<Foo>, IEnumerable<Foo>>>
                  {
                      { SortMethod.Newest, x => x.OrderBy(y => y.Date) },
                      { SortMethod.Oldest, x => x.OrderByDescending(y => y.Date) },
                      { SortMethod.LowestPrice, x => x.OrderBy(y => y.Price) }
                  };

...
var unsorted = new List<Foo>
               {
                   new Foo { Date = new DateTime(2012, 1, 3), Price = 10m },
                   new Foo { Date = new DateTime(2012, 1, 1), Price = 30m },
                   new Foo { Date = new DateTime(2012, 1, 2), Price = 20m }
               };

var sorted = strategyMap[SortMethod.LowestPrice](unsorted);