#region LINQ语法可以让我们在项目使用一种类似于SQL的语法#region 投影查询,查询全部的书籍using (Models.BookStoreEntities db = new Models.BookStoreEntities()){//基于表达式查询var Books = from b in db.Booksselect b;//输出查询结果数量
                    Console.WriteLine(Books.Count());//投影查询除了可以用上述基于表达式的方式实现之外,还可以用一种更简洁的函数方式实现var Books1 = db.Books;Console.WriteLine(Books1.Count());}#endregion#region 条件查询,比如查询书名为JavaScript语言与AJAX应用的书籍编号using (Models.BookStoreEntities db = new Models.BookStoreEntities()){var BookWhere = from b in db.Bookswhere b.Title == "JavaScript语言与AJAX应用"select b;foreach (var book in BookWhere)Console.WriteLine(book.BookId);//同样的查询用函数方式实现var BookWhere2 = db.Books.Where(x => x.Title == "JavaScript语言与AJAX应用");foreach (var item in BookWhere2)Console.WriteLine(item.BookId);//在上述查询中,在函数方式实现的代码中用到了Lambda表达式描述查询条件
                }#endregion#region 排序和分页查询,比如查询全部订单,并按数量排序并分页using (Models.BookStoreEntities db = new Models.BookStoreEntities()) {//按数量排序并分页输出订单编号var Order1 = (from o in db.Ordersorderby o.Numselect o).Skip(0).Take(10);//输出查询结果的编号foreach(var oder in Order1)Console.WriteLine(oder.BookId);//以函数式方式实现查询var Order2 = db.Orders.OrderBy(x => x.Num).Skip(0).Take(10);foreach (var oder2 in Order2)Console.WriteLine(oder2.BookId);}#endregion#region  聚合查询,比如查询书籍总数和价格using (Models.BookStoreEntities db = new Models.BookStoreEntities()) {//书籍总数var num = db.Books.Count();Console.WriteLine(num);var price = db.Books.Min(x => x.Price);Console.WriteLine(price);}#endregion#region 连接查询,比如查询书的订单编号using (Models.BookStoreEntities db = new Models.BookStoreEntities()){var Order3 = from o in db.Ordersjoin b in db.Bookson o.BookId equals b.BookIdselect o;//join关键字用于连接2个数据表,on和equals关键字用于指定的两个表是通过那个字段连接在一起的foreach (var order3 in Order3)Console.WriteLine(order3);}#endregion#endregion