From cb2c3c2c7b141495c4bb768626492afcbcad168d Mon Sep 17 00:00:00 2001
From: Vladimir Pecanac <vladimir.pecanac@gmail.com>
Date: Wed, 23 Sep 2026 14:04:45 +0200
Subject: [PATCH] Outer join in LINQ: retarget net10.0, add LeftJoin and
 RightJoin examples

- Retarget both projects from net8.0 to net10.0.
- Bump test packages: Microsoft.NET.Test.Sdk 18.10.1, xunit 2.9.3,
  xunit.runner.visualstudio 4.0.0, coverlet.collector 10.0.1.
- Add PerformLeftJoinWithLeftJoinMethod and PerformRightJoinWithRightJoinMethod
  using the .NET 10 Enumerable.LeftJoin and Enumerable.RightJoin operators.
- Add two tests for the new methods (8 tests become 10).
- SongWithAuthorComparer: Equals returns the expression directly, and
  GetHashCode combines Title and AuthorName with HashCode.Combine.
- Program.cs prints the two new joins.
---
 ...CreateAnOuterJoinInLINQLeftAndRight.csproj |  2 +-
 .../Program.cs                                | 26 ++++++++++
 .../SongWithAuthorComparer.cs                 |  9 +---
 .../Utilities.cs                              | 32 ++++++++++++
 ...teAnOuterJoinInLINQLeftAndRightUnitTest.cs | 50 +++++++++++++++++++
 .../Tests/Tests.csproj                        | 10 ++--
 6 files changed, 116 insertions(+), 13 deletions(-)

diff --git a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight.csproj b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight.csproj
index 2150e3797b..ed9781c223 100644
--- a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight.csproj
+++ b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/Program.cs b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/Program.cs
index 769e5ee466..d6a0e64c16 100644
--- a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/Program.cs
+++ b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/Program.cs
@@ -52,6 +52,32 @@
 Console.WriteLine();
 Console.WriteLine();
 
+Console.WriteLine("Left outer join - LeftJoin method");
+Console.WriteLine();
+
+results = Utilities.PerformLeftJoinWithLeftJoinMethod(Utilities.Songs, Utilities.Authors);
+
+foreach (var item in results)
+{
+    Console.WriteLine($"Title: {item.Title}, Author: {item.AuthorName}");
+}
+
+Console.WriteLine();
+Console.WriteLine();
+
+Console.WriteLine("Right outer join - RightJoin method");
+Console.WriteLine();
+
+results = Utilities.PerformRightJoinWithRightJoinMethod(Utilities.Songs, Utilities.Authors);
+
+foreach (var item in results)
+{
+    Console.WriteLine($"Title: {item.Title}, Author: {item.AuthorName}");
+}
+
+Console.WriteLine();
+Console.WriteLine();
+
 Console.WriteLine("Full outer join");
 Console.WriteLine();
 
diff --git a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/SongWithAuthorComparer.cs b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/SongWithAuthorComparer.cs
index 8ec28261ae..29e0f19d53 100644
--- a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/SongWithAuthorComparer.cs
+++ b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/SongWithAuthorComparer.cs
@@ -6,16 +6,11 @@ internal class SongWithAuthorComparer : IEqualityComparer<SongWithAuthor>
 {
     public bool Equals(SongWithAuthor? x, SongWithAuthor? y)
     {
-        if (x?.AuthorName == y?.AuthorName && x?.Title == y?.Title)
-        {
-            return true;
-        }
-
-        return false;
+        return x?.AuthorName == y?.AuthorName && x?.Title == y?.Title;
     }
 
     public int GetHashCode([DisallowNull] SongWithAuthor obj)
     {
-        return obj.AuthorName.GetHashCode();
+        return HashCode.Combine(obj.Title, obj.AuthorName);
     }
 }
diff --git a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/Utilities.cs b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/Utilities.cs
index 7c27f5961d..76f14fc56a 100644
--- a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/Utilities.cs
+++ b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/HowToCreateAnOuterJoinInLINQLeftAndRight/Utilities.cs
@@ -92,6 +92,38 @@ public static List<SongWithAuthor> PerformRightJoinWithMethodSyntax(
 
         return results.ToList();
     }
+
+    public static List<SongWithAuthor> PerformLeftJoinWithLeftJoinMethod(
+        List<Song> songs, List<Author> authors)
+    {
+        var results = songs.LeftJoin(
+            authors,
+            song => song.AuthorId,
+            author => author.Id,
+            (song, author) => new SongWithAuthor
+            {
+                Title = song.Title,
+                AuthorName = author?.Name ?? "unknown"
+            });
+
+        return results.ToList();
+    }
+
+    public static List<SongWithAuthor> PerformRightJoinWithRightJoinMethod(
+        List<Song> songs, List<Author> authors)
+    {
+        var results = songs.RightJoin(
+            authors,
+            song => song.AuthorId,
+            author => author.Id,
+            (song, author) => new SongWithAuthor
+            {
+                Title = song?.Title ?? "-",
+                AuthorName = author.Name
+            });
+
+        return results.ToList();
+    }
        
     public static List<SongWithAuthor> PerformFullOuterJoin(
         List<Song> songs, List<Author> authors)
diff --git a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/Tests/HowToCreateAnOuterJoinInLINQLeftAndRightUnitTest.cs b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/Tests/HowToCreateAnOuterJoinInLINQLeftAndRightUnitTest.cs
index 7a5c713c13..ffbcf6f51c 100644
--- a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/Tests/HowToCreateAnOuterJoinInLINQLeftAndRightUnitTest.cs
+++ b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/Tests/HowToCreateAnOuterJoinInLINQLeftAndRightUnitTest.cs
@@ -104,6 +104,56 @@ public void GivenTwoDataSources_WhenPerformRightJoinWithMethodSyntaxMethodCalled
         Assert.Equal(authors.Count, output);
     }
 
+    [Fact]
+    public void GivenTwoDataSources_WhenPerformLeftJoinWithLeftJoinMethodCalled_ThenAllItemsFromLeftSourceAreReturned()
+    {
+        // Arrange
+        List<Song> songs =
+        [
+            new() { Id = 1, Title = "song A", AuthorId = 3 },
+            new() { Id = 2, Title = "song B", AuthorId = 1 },
+            new() { Id = 3, Title = "song C", AuthorId = 5 },
+            new() { Id = 4, Title = "song D", AuthorId = 2 }
+        ];
+
+        List<Author> authors =
+        [
+            new() { Id = 1, Name = "Author A" },
+            new() { Id = 9, Name = "Author B" }
+        ];
+
+        // Act
+        var output = Utilities.PerformLeftJoinWithLeftJoinMethod(songs, authors).Count;
+
+        // Assert
+        Assert.Equal(songs.Count, output);
+    }
+
+    [Fact]
+    public void GivenTwoDataSources_WhenPerformRightJoinWithRightJoinMethodCalled_ThenAllItemsFromRightSourceAreReturned()
+    {
+        // Arrange
+        List<Song> songs =
+        [
+            new() { Id = 1, Title = "song A", AuthorId = 3 },
+            new() { Id = 2, Title = "song B", AuthorId = 1 },
+            new() { Id = 3, Title = "song C", AuthorId = 5 },
+            new() { Id = 4, Title = "song D", AuthorId = 2 }
+        ];
+
+        List<Author> authors =
+        [
+            new() { Id = 1, Name = "Author A" },
+            new() { Id = 9, Name = "Author B" }
+        ];
+
+        // Act
+        var output = Utilities.PerformRightJoinWithRightJoinMethod(songs, authors).Count;
+
+        // Assert
+        Assert.Equal(authors.Count, output);
+    }
+
     [Fact]
     public void GivenTwoDataSources_WhenPerformFullOuterJoinMethodCalled_ThenAllItemsFromBothSourcesAreReturned()
     {
diff --git a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/Tests/Tests.csproj b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/Tests/Tests.csproj
index 615d2e1e84..b79bfbeb8f 100644
--- a/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/Tests/Tests.csproj
+++ b/csharp-linq/HowToCreateAnOuterJoinInLINQLeftAndRight/Tests/Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 
@@ -10,13 +10,13 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.6.0" />
-    <PackageReference Include="xunit" Version="2.4.2" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.10.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.0">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
-    <PackageReference Include="coverlet.collector" Version="6.0.0">
+    <PackageReference Include="coverlet.collector" Version="10.0.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>