Provide Perform inner joins article with method-based syntax examples (#36376)

* Implement method syntax approach for each inner join example

* Invoke the method-syntax methods in Program

* Adjust tests to cover the equality between query and method syntax results

* Add the method-syntax examples to the Inner Joins page

* Correct capitalization of a note for grouped joins

Co-authored-by: Bill Wagner <[email protected]>

* Use 2nd person for advices in Inner joins docs

Co-authored-by: Bill Wagner <[email protected]>

---------

Co-authored-by: Bill Wagner <[email protected]>

Author: BartoszKlonowski

docs/csharp/linq/perform-inner-joins.md

@@ -31,6 +31,10 @@ The following example creates two collections that contain objects of two user-d
 
 :::code language="csharp" source="../../../samples/snippets/csharp/concepts/linq/LinqSamples/InnerJoins.cs" id="inner_joins_1":::
 
+You achieve the same results using the <xref:System.Linq.Enumerable.Join%2A> method syntax:
+
+:::code language="csharp" source="../../../samples/snippets/csharp/concepts/linq/LinqSamples/InnerJoins.cs" id="inner_joins_method_syntax_1":::
+
 Note that the `Person` object whose `LastName` is "Huff" does not appear in the result set because there is no `Pet` object that has `Pet.Owner` equal to that `Person`.
 
 ## Example - Composite key join
@@ -41,6 +45,10 @@ The following example uses a list of `Employee` objects and a list of `Student`
 
 :::code language="csharp" source="../../../samples/snippets/csharp/concepts/linq/LinqSamples/InnerJoins.cs" id="inner_joins_2":::
 
+You can use the <xref:System.Linq.Enumerable.Join%2A> method, as shown in the following example:
+
+:::code language="csharp" source="../../../samples/snippets/csharp/concepts/linq/LinqSamples/InnerJoins.cs" id="inner_joins_method_syntax_2":::
+
 ## Example - Multiple join
 
 Any number of join operations can be appended to each other to perform a multiple join. Each `join` clause in C# correlates a specified data source with the results of the previous join.
@@ -53,6 +61,10 @@ The second `join` clause in C# correlates the anonymous types returned by the fi
 
 :::code language="csharp" source="../../../samples/snippets/csharp/concepts/linq/LinqSamples/InnerJoins.cs" id="inner_joins_3":::
 
+The equivalent using multiple <xref:System.Linq.Enumerable.Join%2A> method uses the same approach with the anonymous type (in the example below it's named `commonOwner`):
+
+:::code language="csharp" source="../../../samples/snippets/csharp/concepts/linq/LinqSamples/InnerJoins.cs" id="inner_joins_method_syntax_3":::
+
 ## Example - Inner join by using grouped join
 
 The following example shows you how to implement an inner join by using a group join.
@@ -65,6 +77,14 @@ The result of `query1` is equivalent to the result set that would have been obta
 
 :::code language="csharp" source="../../../samples/snippets/csharp/concepts/linq/LinqSamples/InnerJoins.cs" id="inner_joins_4":::
 
+The same results can be achieved using <xref:System.Linq.Enumerable.GroupJoin%2A> method, as follows:
+
+:::code language="csharp" source="../../../samples/snippets/csharp/concepts/linq/LinqSamples/InnerJoins.cs" id="inner_joins_method_syntax_4":::
+
+Note that this approach requires chaining the query results with <xref:System.Linq.Enumerable.SelectMany%2A> to create the final list of Owner - Pet relation based on the results of group join. To avoid chaining, the single <xref:System.Linq.Enumerable.Join%2A> method can be used as presented below:
+
+:::code language="csharp" source="../../../samples/snippets/csharp/concepts/linq/LinqSamples/InnerJoins.cs" id="inner_joins_method_syntax_5":::
+
 ## See also
 
 - <xref:System.Linq.Enumerable.Join%2A>

samples/snippets/csharp/concepts/linq/LinqSamples.Test/InnerJoinsTest.cs

@@ -8,50 +8,54 @@ public class InnerJoinsTest
     [Fact]
     public void BasicTest()
     {
-        var sw = InitTest();
-
-        InnerJoins.Basic();
-        Assert.Equal(
+        const string expectedOutput =
 @"""Daisy"" is owned by Magnus
 ""Barley"" is owned by Terry
 ""Boots"" is owned by Terry
 ""Whiskers"" is owned by Charlotte
 ""Blue Moon"" is owned by Rui
-", sw.ToString());
+";
+
+        var querySyntaxResult = InnerJoins.Basic();
+        Assert.Equal(expectedOutput, querySyntaxResult);
+
+        var methodSyntaxResult = InnerJoins.BasicMethodSyntax();
+        Assert.Equal(methodSyntaxResult, querySyntaxResult);
     }
 
     [Fact]
     public void CompositeKeyTest()
     {
-        var sw = InitTest();
-
-        InnerJoins.CompositeKey();
-        Assert.Equal(
+        const string expectedOutput =
 @"The following people are both employees and students:
 Terry Adams
 Vernette Price
-", sw.ToString());
+";
+        var querySyntaxResult = InnerJoins.CompositeKey();
+        Assert.Equal(expectedOutput, querySyntaxResult);
+
+        var methodSyntaxResult = InnerJoins.CompositeKeyMethodSyntax();
+        Assert.Equal(methodSyntaxResult, querySyntaxResult);
     }
 
     [Fact]
     public void MultipleJoinTest()
     {
-        var sw = InitTest();
-
-        InnerJoins.MultipleJoin();
-        Assert.Equal(
+        const string expectedOutput =
 @"The cat ""Daisy"" shares a house, and the first letter of their name, with ""Duke"".
 The cat ""Whiskers"" shares a house, and the first letter of their name, with ""Wiley"".
-", sw.ToString());
+";
+        var querySyntaxResult = InnerJoins.MultipleJoin();
+        Assert.Equal(expectedOutput, querySyntaxResult);
+
+        var methodSyntaxResult = InnerJoins.MultipleJoinMethodSyntax();
+        Assert.Equal(methodSyntaxResult, querySyntaxResult);
     }
 
     [Fact]
     public void InnerGroupJoinTest()
     {
-        var sw = InitTest();
-
-        InnerJoins.InnerGroupJoin();
-        Assert.Equal(
+        const string expectedOutput =
 @"Inner join using GroupJoin():
 Magnus - Daisy
 Terry - Barley
@@ -65,6 +69,11 @@ public void InnerGroupJoinTest()
 Terry - Boots
 Terry - Blue Moon
 Charlotte - Whiskers
-", sw.ToString());
+";
+        var querySyntaxResult = InnerJoins.InnerGroupJoin();
+        Assert.Equal(expectedOutput, querySyntaxResult);
+
+        var methodSyntaxResult = InnerJoins.InnerGroupJoinMethodSyntax();
+        Assert.Equal(methodSyntaxResult, querySyntaxResult);
     }
 }