Left join extension method

LeftJoinExtension.cs

public static class QueryableExtensions {
	public static IQueryable<TResult> LeftJoin<TOuter, TInner, TKey, TResult> (
		this IQueryable<TOuter> outer,
		IQueryable<TInner> inner,
		Expression<Func<TOuter, TKey>> outerKeySelector,
		Expression<Func<TInner, TKey>> innerKeySelector,
		Expression<Func<JoinResult<TOuter, TInner>, TResult>> resultSelector) {
		var result = outer
			.GroupJoin(inner, outerKeySelector, innerKeySelector, (outer1, inners) => new { outer1, inners = inners.DefaultIfEmpty() })
			.SelectMany(row => row.inners, (row, inner1) => new JoinResult<TOuter, TInner> { Outer = row.outer1, Inner = inner1 })
			.Select(resultSelector);

		return result;
	}

	public class JoinResult<TOuter, TInner> {
		public TOuter Outer { get; set; }
		public TInner Inner { get; set; }
	}
}