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 products
103 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 numbers
137 where n < 5
138 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 numbersA
156 from b in numbersB
157 where a < b
158 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 customers
175 from o in c.Orders
176 where o.Total < 500
177 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 customers
190 from o in c.Orders
191 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 customers
205 from o in c.Orders
206 where o.Total > 2000
207 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 customers
221 // from o in c.Orders
222 // 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 customers
226 where c.Region == "WA"
227 from o in c.Orders
228 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 }
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