Question

I want to get the method System.Linq.Queryable.OrderyBy<T, TKey>(the IQueryable<T> source, Expression<Func<T,TKey>> keySelector) method, but I keep coming up with nulls.

var type = typeof(T); var propertyInfo = type.GetProperty(group.PropertyName); var propertyType = propertyInfo.PropertyType;  var sorterType = typeof(Func<,>).MakeGenericType(type, propertyType); var expressionType = typeof(Expression<>).MakeGenericType(sorterType);  var queryType = typeof(IQueryable<T>);  var orderBy = typeof(System.Linq.Queryable).GetMethod('OrderBy', new[] { queryType, expressionType }); /// is always null. 

Does anyone have any insight? I would prefer to not loop through the GetMethods result.

Answer 1

Solved (by hacking LINQ)!

I saw your question while researching the same problem. After finding no good solution, I had the idea to look at the LINQ expression tree. Here’s what I came up with:

public static MethodInfo GetOrderByMethod<TElement, TSortKey>() {     Func<TElement, TSortKey> fakeKeySelector = element => default(TSortKey);      Expression<Func<IEnumerable<TElement>, IOrderedEnumerable<TElement>>> lamda         = list => list.OrderBy(fakeKeySelector);      return (lamda.Body as MethodCallExpression).Method; }  static void Main(string[] args) {     List<int> ints = new List<int>() { 9, 10, 3 };     MethodInfo mi = GetOrderByMethod<int, string>();                Func<int,string> keySelector = i => i.ToString();     IEnumerable<int> sortedList = mi.Invoke(null, new object[] { ints,                                                                   keySelector }                                            ) as IEnumerable<int>;      foreach (int i in sortedList)     {         Console.WriteLine(i);     } } 

output: 10 3 9

EDIT: Here is how to get the method if you don’t know the type at compile-time:

public static MethodInfo GetOrderByMethod(Type elementType, Type sortKeyType) {     MethodInfo mi = typeof(Program).GetMethod('GetOrderByMethod', Type.EmptyTypes);      var getOrderByMethod = mi.MakeGenericMethod(new Type[] { elementType,                                                              sortKeyType });     return getOrderByMethod.Invoke(null, new object[] { }) as MethodInfo; } 

Be sure to replace typeof(Program) with typeof(WhateverClassYouDeclareTheseMethodsIn).