andrew-t-moore

public class Person {
	public int Id { get; set; }
	public string FirstName { get; set; }
	public string LastName { get; set; }
}

public class Pet {
	public int Id { get; set; }
	public string Name { get; set; }
	public Person Owner { get; set; }

andrew-t-moore

var query = context.Person
	.GroupJoin(context.Pet, 
		person => person, 
		pet => pet.Owner, 
		(person, pets) => new { person, pets = pets.DefaultIfEmpty() })
	.SelectMany(group => group.pets, 
		(row, pet) => new { row.person.FirstName, row.person.LastName, PetName = pet.Name });

andrew-t-moore

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 })

andrew-t-moore

var query2 = context.Person
	.LeftJoin(context.Pet, 
		person => person, 
		pet => pet.Owner, 
		row => new { row.Outer.FirstName, row.Outer.LastName, PetName = row.Inner.Name });