1 using System;
2 using System.Collections.Generic;
3 using System.Linq;
4
5 namespace Linq101
6 {
7 internal class Join
8 {
9 /// <summary>
10 /// This sample shows how to efficiently join elements of two sequences based on equality between key expressions over the two.
11 /// </summary>
12 public void Linq102()
13 {
14 string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
15 List<Data.Product> products = Data.GetProductList();
16
17 var q = from c in categories
18 join p in products on c equals p.Category
19 select new { Category = c, p.ProductName };
20
21 ObjectDumper.Write(q);
22 }
23
24 /// <summary>
25 /// Using a group join you can get all the products that match a given category bundled as a sequence.
26 /// </summary>
27 public void Linq103()
28 {
29 string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
30 List<Data.Product> products = Data.GetProductList();
31
32 var q = from c in categories
33 join p in products on c equals p.Category into ps
34 select new { Category = c, Products = ps };
35
36 foreach (var v in q)
37 {
38 Console.WriteLine(v.Category + ":");
39 foreach (var p in v.Products)
40 {
41 Console.WriteLine(" " + p.ProductName);
42 }
43 }
44 }
45
46 /// <summary>
47 /// The group join operator is more general than join, as this slightly more verbose version of the cross join sample shows.
48 /// </summary>
49 public void Linq104()
50 {
51 string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
52 List<Data.Product> products = Data.GetProductList();
53
54 var q = from c in categories
55 join p in products on c equals p.Category into ps
56 from p in ps
57 select new { Category = c, p.ProductName };
58
59 foreach (var v in q)
60 {
61 Console.WriteLine(v.ProductName + ": " + v.Category);
62 }
63 }
64
65 /// <summary>
66 /// A so-called outer join can be expressed with a group join. A left outer joinis like a cross join,
67 /// except that all the left hand side elements get included at least once, even if they don't match any right hand side elements.
68 /// Note how Vegetablesshows up in the output even though it has no matching products.
69 /// </summary>
70 public void Linq105()
71 {
72 string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
73 List<Data.Product> products = Data.GetProductList();
74
75 var q = from c in categories
76 join p in products on c equals p.Category into ps
77 from p in ps.DefaultIfEmpty()
78 select new { Category = c, ProductName = p == null ? "(No Products)" : p.ProductName };
79
80 foreach (var v in q)
81 {
82 Console.WriteLine(v.ProductName + ": " + v.Category);
83 }
84 }
85 }
86 }
