The Devlineator

We have all at one time or another gotten a user request for sorts based on columns. If that is a pre-built control it most likely has this, and if it is home grown then it will probably need some work. You could write a sort for every column or you could write on that takes the column name in and sorts based on a string. LINQ however doesn’t like this. If you want string based sorting then you must do either a really nasty case statement or use a sort extension like this one.

public static class LinqSortExtensions
{
    private const string Ascending = "ASC";

    public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property, string dirrection)
    {
        return dirrection == Ascending ? source.OrderBy(property) : source.OrderByDescending(property);
    }

    public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
    {
        return ApplyOrder(source, property, "OrderBy");
    }
    public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
    {
        return ApplyOrder(source, property, "OrderByDescending");
    }
    public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property, string dirrection)
    {
        return dirrection == Ascending ? source.ThenBy(property) : source.ThenByDescending(property);
    }
    public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
    {
        return ApplyOrder(source, property, "ThenBy");
    }
    public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)
    {
        return ApplyOrder(source, property, "ThenByDescending");
    }
    static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName)
    {
        var props = property.Split('.');
        var type = typeof(T);
        var arg = Expression.Parameter(type, "x");
        Expression expr = arg;
        foreach (var pi in props.Select(prop => type.GetProperty(prop)))
        {
            expr = Expression.Property(expr, pi);
            type = pi.PropertyType;
        }
        var delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
        var lambda = Expression.Lambda(delegateType, expr, arg);

        var result = typeof(Queryable).GetMethods().Single(
                method => method.Name == methodName
                        && method.IsGenericMethodDefinition
                        && method.GetGenericArguments().Length == 2
                        && method.GetParameters().Length == 2)
                .MakeGenericMethod(typeof(T), type)
                .Invoke(null, new object[] { source, lambda });
        return (IOrderedQueryable<T>)result;
    }

This allows you to pass in a property name and a direction. It allows for multiple sorts, and in case some out there want them, here are the unit tests too..

[TestFixture]
    public class QueryTests
    {

        [Test]
        public void CanSortWithOnlyStrings()
        {
            IQueryable<TestObject> items = new List<TestObject>()
                            {
                                new TestObject(){id = 1, Test = "Test1"},
                                new TestObject(){id = 3, Test = "Test3"},
                                new TestObject(){id = 2, Test = "Test2"},
                               
                            }.AsQueryable();

            Assert.AreEqual(2, items.OrderBy("id", "ASC").ToArray()[1].id);
        }

        [Test]
        public void CanSortDescendingWithOnlyString()
        {
            IQueryable<TestObject> items = new List<TestObject>()
                            {
                                new TestObject(){id = 1, Test = "Test1"},
                                new TestObject(){id = 3, Test = "Test3"},
                                new TestObject(){id = 2, Test = "Test2"},
                               
                            }.AsQueryable();

            Assert.AreEqual(1, items.OrderBy("id", "DSC").ToArray()[2].id);

        }

        [Test]
        public void CanSortMultipleTimesAscending()
        {
            IQueryable<TestObject> items = new List<TestObject>()
                            {
                                 new TestObject(){id = 1, Test = "Test1"},
                                new TestObject(){id = 3, Test = "Test3"},
                                new TestObject(){id = 2, Test = "Test3"},
                                new TestObject(){id = 2, Test = "Test2"},
                                new TestObject(){id = 2, Test = "Test1"}
                               
                            }.AsQueryable();
            var item = items.OrderBy("id", "ASC").ThenBy("Test", "ASC").ToArray()[3];
            Assert.AreEqual("Test3", item.Test);
        }

        [Test]
        public void CanSortMultipleTimesWithMultipleDirrections()
        {
            IQueryable<TestObject> items = new List<TestObject>()
                            {
                                new TestObject(){id = 1, Test = "Test1"},
                                new TestObject(){id = 3, Test = "Test3"},
                                new TestObject(){id = 2, Test = "Test3"},
                                new TestObject(){id = 2, Test = "Test2"},
                                new TestObject(){id = 2, Test = "Test1"}
                               
                            }.AsQueryable();
            var item = items.OrderBy("id", "ASC").ThenBy("Test", "DSC").ToArray()[3];
            Assert.AreEqual("Test1", item.Test);

        }
    }

    public class TestObject
    {
        public int id { get; set; }
        public string Test { get; set; }
    }

Enjoy