1 using System;  2 using System.Linq;  3   4 namespace Linq101  5 {  6     class Projection  7     {  8         /// <summary>  9         /// This sample uses select to produce a sequence of ints one higher than those in an existing array of ints. 10         /// </summary> 11         public void Linq6() 12         { 13             int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 14  15             var query = from n in numbers 16                         select n + 1; 17  18             Console.WriteLine("Numbers + 1 :"); 19             foreach (var i in query) 20             { 21                 Console.WriteLine(i); 22             } 23         } 24  25         /// <summary> 26         /// This sample uses select to return a sequence of just the names of a list of products. 27         /// </summary> 28         public void Linq7() 29         { 30             var products = Data.GetProductList(); 31  32             var query = from p in products 33                         select p.ProductName; 34  35             Console.WriteLine("Product Names:"); 36             foreach (var productName in query) 37             { 38                 Console.WriteLine(productName); 39             } 40         } 41  42         /// <summary> 43         /// This sample uses select to produce a sequence of strings representing the text version of a sequence of ints. 44         /// </summary> 45         public void Linq8() 46         { 47             int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 48             string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; 49  50             var query = from n in numbers 51                         select strings[n]; 52  53             Console.WriteLine("Number strings:"); 54             foreach (var s in query) 55             { 56                 Console.WriteLine(s); 57             } 58         } 59  60         /// <summary> 61         /// This sample uses select to produce a sequence of the uppercase and lowercase versions of each word in the original array. 62         /// </summary> 63         public void Linq9() 64         { 65             string[] words = { "aPPLE", "BlUeBeRrY", "cHeRry" }; 66  67             var query = from w in words 68                         select new { U = w.ToUpper(), L = w.ToLower() }; 69  70             Console.WriteLine("Results:"); 71             foreach (var item in query) 72             { 73                 Console.WriteLine("Uppercase:{0},Lowercase:{1}", item.U, item.L); 74             } 75         } 76  77         /// <summary> 78         /// This sample uses select to produce a sequence containing text representations of digits and whether their length? is even or odd. 79         /// </summary> 80         public void Linq10() 81         { 82             int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 83             string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; 84  85             var query = from n in numbers 86                         select new { Digit = strings[n], EorO = n % 2 == 0 ? "Even" : "Odd" }; 87  88             Console.WriteLine("Results:"); 89             foreach (var item in query) 90             { 91                 Console.WriteLine("The digit {0} is {1}", item.Digit, item.EorO); 92             } 93         } 94  95         /// <summary> 96         /// This sample uses select to produce a sequence containing some properties of Products, including UnitPrice which is renamed to Price in the resulting type. 97         /// </summary> 98         public void Linq11() 99         {100             var products = Data.GetProductList();101 102             var query = from p in products103                         select new { p.ProductName, p.Category, Price = p.UnitPrice };104 105             Console.WriteLine("Product Info:");106             foreach (var product in query)107             {108                 Console.WriteLine("{0} is in the category {1} and cost {2} per unit", product.ProductName, product.Category, product.Price);109             }110         }111 112         /// <summary>113         /// This sample uses an indexed Select clause to determine if the value of ints in an array match their position in the array.114         /// </summary>115         public void Linq12()116         {117             int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };118 119             var query = numbers.Select((n, index) => new { Num = n, InPlace = n == index });120 121             Console.WriteLine("Number:In-place?");122             foreach (var number in query)123             {124                 Console.WriteLine("{0}:{1}", number.Num, number.InPlace);125             }126         }127 128         /// <summary>129         /// This sample combines select and where to make a simple query that returns the text form of each digit less than 5.130         /// </summary>131         public void Linq13()132         {133             int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };134             string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };135 136             var query = from n in numbers137                         where n < 5138                         select digits[n];139 140             Console.WriteLine("Numbers < 5:");141             foreach (var digit in query)142             {143                 Console.WriteLine(digit);144             }145         }146 147         /// <summary>148         /// This sample uses a compound from clause to make a query that returns all pairs of numbers from both arrays such that the number from numbersA is less than the number from numbersB.149         /// </summary>150         public void Linq14()151         {152             int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };153             int[] numbersB = { 1, 3, 5, 7, 8 };154 155             var query = from a in numbersA156                         from b in numbersB157                         where a < b158                         select new { a, b };159 160             Console.WriteLine("Pairs where a < b");161             foreach (var pair in query)162             {163                 Console.WriteLine("{0} is less than {1}", pair.a, pair.b);164             }165         }166 167         /// <summary>168         /// This sample uses a compound from clause to select all orders where the order total is less than 500.00.169         /// </summary>170         public void Linq15()171         {172             var customers = Data.GetCustomerList();173 174             var query = from c in customers175                         from o in c.Orders176                         where o.Total < 500177                         select new { c.CustomerID, o.OrderID, o.Total };178 179             ObjectDumper.Write(query);180         }181 182         /// <summary>183         /// This sample uses a compound from clause to select all orders where the order was made in 1998 or later.184         /// </summary>185         public void Linq16()186         {187             var customers = Data.GetCustomerList();188 189             var query = from c in customers190                         from o in c.Orders191                         where o.OrderDate >= new DateTime(1998, 1, 1)192                         select new { c.CustomerID, o.OrderID, o.OrderDate };193 194             ObjectDumper.Write(query);195         }196 197         /// <summary>198         /// This sample uses a compound from clause to select all orders where the order total is greater than 2000.00 and uses from assignment to avoid requesting the total twice.199         /// </summary>200         public void Linq17()201         {202             var customers = Data.GetCustomerList();203 204             var query = from c in customers205                         from o in c.Orders206                         where o.Total > 2000207                         select new { c.CustomerID, o.OrderID, o.Total };208 209             ObjectDumper.Write(query);210         }211 212         /// <summary>213         /// This sample uses multiple from clauses so that filtering on customers can be done before selecting their orders. This makes the query more efficient by not selecting and then discarding orders for customers outside of Washington.214         /// </summary>215         public void Linq18()216         {217             var customers = Data.GetCustomerList();218 219             //效率低220             //var query = from c in customers221             //            from o in c.Orders222             //            where c.Region == "WA" && o.OrderDate >= new DateTime(1997, 1, 1)223             //            select new { c.CustomerID, o.OrderID };224 225             var query = from c in customers226                         where c.Region == "WA"227                         from o in c.Orders228                         where o.OrderDate >= new DateTime(1997, 1, 1)229                         select new { c.CustomerID, o.OrderID };230 231             ObjectDumper.Write(query);232         }233 234         /// <summary>235         /// This sample uses an indexed SelectMany clause to select all orders, while referring to customers by the order in which they are returned from the query.236         /// </summary>237         public void Linq19()238         {239             var customers = Data.GetCustomerList();240 241             //var query = customers.SelectMany(c => c.Orders);242             //var query = customers.SelectMany(c => c.Orders).Where(o => o.OrderDate >= new DateTime(1998, 1, 1));243             var query =244                 customers.SelectMany(245                     (customer, index) =>246                         (customer.Orders.Select(o => "Customer #" + (index + 1) + " has an order with OrderID " + o.OrderID)));247 248             ObjectDumper.Write(query);249         }250     }251 }