System.Linq.Expressions.Expression for .OrderBy function

Question

I have a line of my code that repeats.

You will see the lambda expression under repeat 4 times

x => x.GetValue<string>("City")).ThenByDescending(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"), x.GetValue<string[]>("EventTimeZone")[0].ToString()) 

Code example:

 //SORT DATA switch (SortDetails) { case ("Date"): default: if (SortOrder == "ASC") { _allEvents = _allEvents.OrderBy(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"), x.GetValue<string[]>("EventTimeZone")[0].ToString())); } else { _allEvents = _allEvents.OrderByDescending(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"), x.GetValue<string[]>("EventTimeZone")[0].ToString())); } break; case ("Location"): if (SortOrder == "ASC") { _allEvents = _allEvents.OrderBy(x => x.GetValue<string>("Country")).ThenBy(x => x.GetValue<string>("ProvinceState")).ThenBy(x => x.GetValue<string>("City")).ThenBy(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"), x.GetValue<string[]>("EventTimeZone")[0].ToString())); } else { _allEvents = _allEvents.OrderByDescending(x => x.GetValue<string>("Country")).ThenByDescending(x => x.GetValue<string>("ProvinceState")).ThenByDescending(x => x.GetValue<string>("City")).ThenByDescending(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"), x.GetValue<string[]>("EventTimeZone")[0].ToString())); } break; } 

I would like to take the first line and make it something that I can just spit on OrderBy's.

Sort of:

 System.Linq.Expressions.Expression<Func<DynamicContent, DateTime>> sortLambda = x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"), x.GetValue<string[]>("EventTimeZone")[0].ToString()); 

in:

 allEvents = _allEvents.OrderBy(sortLambda); 

Unfortunately, this did not work.

Answer 1

This console application should fix you. SortLamda can be of any type, which I hope answers your question about dynamic content.

 using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Linq.Expressions; internal class BoringEvent { public string EventStartStr { get; set; } public string EventTimeZone { get; set; } public string ProvinceState { get; set; } public string City { get; set; } public string Country { get; set; } } internal enum SortedBy { Ascending = 0, Descending } class ExpressionsTest { internal static List<BoringEvent> _allEvents = new List<BoringEvent>(); internal static class HelperFunctions { public static DateTime strToTZDateTime(string startDate, string timeZone) { //I'm too lazy to figure out dates by time zone. //Your function already has the logic, so why bother. //Let assume the time zone is equal in this test case return DateTime.Parse(startDate); } } internal static void Main() { _allEvents.Add(new BoringEvent { EventStartStr = "12/31/1999", //let party like it 1999 - (yawn) I'm stuck at this event :< EventTimeZone = "en-us", City = "Philadelphia", ProvinceState = "Pennsylvania", Country = "United States of America"}); _allEvents.Add(new BoringEvent { EventStartStr = "01/01/1970", EventTimeZone = "en-us", City = "New York", ProvinceState = "New York", Country = "United States of America" }); IEnumerable<BoringEvent> sortedEvents = null; //sort by date Console.WriteLine("Sorting Events by Ascending date..."); Expression<Func<BoringEvent, DateTime>> sortLamba = evt => HelperFunctions.strToTZDateTime(evt.EventStartStr, evt.EventTimeZone); sortedEvents = _allEvents.SortEvents(SortedBy.Ascending, sortLamba); Print(sortedEvents); //sort by country, then state, then city, then date Console.WriteLine("Sorting Events Desc by Country, then ProvinceState, then City, then Date"); Expression<Func<BoringEvent, object>>[] sortLamba2 = new Expression<Func<BoringEvent, object>>[] { evt => evt.Country, evt => evt.ProvinceState, evt => evt.City, evt => HelperFunctions.strToTZDateTime(evt.EventStartStr, evt.EventTimeZone) }; sortedEvents = _allEvents.SortEvents(SortedBy.Descending, sortLamba2); Print(sortedEvents); Console.Read(); } private static void Print(IEnumerable<BoringEvent> events) { for(int i = 0; i < events.Count(); i++) { BoringEvent evt = events.ElementAt(i); Console.WriteLine("Event: {0}", i.ToString()); Console.WriteLine("\tEventStartStr: {0}", evt.EventStartStr); Console.WriteLine("\tEventTimeZone: {0}", evt.EventTimeZone); Console.WriteLine("\tCity: {0}", evt.City); Console.WriteLine("\tProvinceState: {0}", evt.ProvinceState); Console.WriteLine("\tCountry: {0}", evt.Country); } } } internal static class EventExtensions { public static IEnumerable<TResult> SortEvents<TResult, T>( this IEnumerable<TResult> events, SortedBy sortByType, params Expression<Func<TResult, T>>[] expressions) { IEnumerable<TResult> retVal = null; switch(sortByType) { case SortedBy.Ascending: retVal = EventExtensions.SortEventsAsc(events, expressions); break; case SortedBy.Descending: retVal = EventExtensions.SortEventsDesc(events, expressions); break; default: throw new InvalidOperationException( string.Format("The SortedBy enumeration does not contain a case for the value of '{0}'.", Enum.GetName(typeof(SortedBy), sortByType))); } return retVal; } public static IEnumerable<TResult> SortEventsAsc<TResult, T>( this IEnumerable<TResult> events, params Expression<Func<TResult, T>>[] expressions) { IOrderedEnumerable<TResult> sorted = null; for(int i = 0; i < expressions.Count(); i++) { Expression<Func<TResult, T>> exp = (Expression<Func<TResult, T>>)expressions[i]; Func<TResult, T> deleg = exp.Compile(); if(i == 0) { sorted = events.OrderBy(evt => deleg.Invoke(evt)); } else { sorted = sorted.ThenBy(evt => deleg.Invoke(evt)); } } return sorted; } public static IEnumerable<TResult> SortEventsDesc<TResult, T>( this IEnumerable<TResult> events, params Expression<Func<TResult, T>>[] expressions) { IOrderedEnumerable<TResult> sorted = null; for (int i = 0; i < expressions.Count(); i++) { Expression<Func<TResult, T>> exp = (Expression<Func<TResult, T>>)expressions[i]; Func<TResult, T> deleg = exp.Compile(); if (i == 0) { sorted = events.OrderByDescending(evt => deleg.Invoke(evt)); } else { sorted = sorted.ThenByDescending(evt => deleg.Invoke(evt)); } } return sorted; } } 

Answer 2

I believe the OrderBy method accepts the parameter Func<T1,T2> , so you can do this ...

 var func = x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"), x.GetValue<string[]>("EventTimeZone")[0].ToString()); 

then go func to _allEvents = _allEvents.OrderBy(func);