.NET Fiddle

CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
					
public class Program
{
	public class Book {
		public int BookId { get; set; }
		public string Title { get; set; }
	}
	
	public class BookLoan {
		public int BookId { get; set; }
		public DateTime CheckedOutOn { get; set; }
		public DateTime? ReturnedOn { get; set; }
		public DateTime DueOn { get; set; }
	}
	
	public class BookViewModel {
		public int BookId { get; set; }
		public string Title { get; set; }
		public bool IsAvailable { get; set; }
		public DateTime? AvailableOn { get; set; }
	} 
	
	
	
	public static void Main()
	{
		var books = new List<Book> {
			new Book { BookId = 1, Title = "Book 1" },
			new Book { BookId = 2, Title = "Book 2" },
			new Book { BookId = 3, Title = "Book 3" }
		};
		
		var loans = new List<BookLoan> {
			new BookLoan { BookId = 1, CheckedOutOn = new DateTime(2016, 1, 3), DueOn = new DateTime(2016, 2, 4), ReturnedOn = new DateTime(2016, 2, 3)},
			new BookLoan { BookId = 1, CheckedOutOn = new DateTime(2016, 6, 9), DueOn = new DateTime(2016, 7, 4), ReturnedOn = null },
			new BookLoan { BookId = 2, CheckedOutOn = new DateTime(2016, 4, 5), DueOn = new DateTime(2016, 5, 3), ReturnedOn = new DateTime(2016, 5, 23)},
			new BookLoan { BookId = 2, CheckedOutOn = new DateTime(2016, 6, 1), DueOn = new DateTime(2016, 8, 4), ReturnedOn = new DateTime(2016, 7, 5)},
			new BookLoan { BookId = 3, CheckedOutOn = new DateTime(2016, 1, 9), DueOn = new DateTime(2016, 2, 4), ReturnedOn = null }
		};
		
		var viewModel = from book in books
            join loan in loans.Where(x => !x.ReturnedOn.HasValue) on book.BookId equals loan.BookId into result
            from loanWithDefault in result.DefaultIfEmpty()
            select new BookViewModel { 
                BookId = book.BookId,
                Title = book.Title,
                IsAvailable = loanWithDefault == null,
				AvailableOn = loanWithDefault == null ? (DateTime?) null : loanWithDefault.DueOn
            };
		
		
		
		Console.WriteLine("Available: ");
		viewModel.Where(x => x.IsAvailable).ToList().ForEach(x => Console.WriteLine(x.Title));
		Console.WriteLine("\nUnavailable: ");
		viewModel.Where(x => !x.IsAvailable).ToList().ForEach(x => Console.WriteLine(x.Title + " - available " + x.AvailableOn));
	}
}