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Errata (58 items)

If you find any mistakes in the sixth edition, C# 10 and .NET 6 - Modern Cross-Platform Development, then please raise an issue in this repository or email me at markjprice (at) gmail.com.

Page 3 - Pros and cons of the .NET Interactive Notebooks extension

The .NET Interactive Notebooks extension has been renamed to Polyglot Notebooks. It still retains its original identifier ms-dotnettools.dotnet-interactive-vscode.

Read more here: https://devblogs.microsoft.com/dotnet/dotnet-interactive-notebooks-is-now-polyglot-notebooks/#why-the-name-change

I wrote that "They cannot read input from the user, for example, you cannot use ReadLine or ReadKey." Although you cannot use the Console class methods, you can use the Microsoft.DotNet.Interactive.Kernel class and its GetInputAsync method. This uses the Visual Studio Code user interface to prompt the user for input.

Page 6 - Downloading and installing Visual Studio 2022 for Windows

Thanks to Bert_the_Dad who raised this issue on 1 July 2023.

In Step 3, I list the Workloads to select to install, including Mobile development with .NET. I should have written .NET Multi-platform App UI development. This workload is only needed for the optional online-only Chapter 19, Building Mobile and Desktop Apps Using .NET MAUI.

Page 7, 8 - Downloading and installing Visual Studio Code

The .NET Interactive Notebooks extension has been renamed to Polyglot Notebooks. It still retains its original identifier ms-dotnettools.dotnet-interactive-vscode.

In Step 2, I wrote to "install the .NET SDKs for versions 3.1, 5.0, and 6.0". You can continue to do so even after an SDK version reaches end-of-life because it will still work. However, you may prefer to install .NET 6 and .NET 7 SDKs once .NET Core 3.1 and .NET 5 reach their end-of-life.

https://dotnet.microsoft.com/en-us/download/dotnet/5.0

Page 8 - Installing other extensions

Thanks to ifduyue for raising this issue on 14 November 2021.

In the table of extensions, the identifier for MSBuild project tools should be tintoy not tinytoy.

The .NET Interactive Notebooks extension has been renamed to Polyglot Notebooks. It still retains its original identifier ms-dotnettools.dotnet-interactive-vscode.

In the table, the C# for Visual Studio Code extension says it is "powered by OmniSharp". This is true up to the most recent release version 1.25.9. But if you install the pre-release version 2.0.x then it does not include OmniSharp any more.

To follow the instructions in the book, if you have installed the pre-release version 2.0.x then on the C# extension page, I recommend that you click the button Switch to Release Version to revert back to the current release version 1.25.9.

If you have installed the C# Dev Kit then it will install the pre-release version of the C# extension.

Page 18, 19 - Writing code using Visual Studio 2022

In Step 3, the project template name has been changed from Console Application to Console App in the final release of Visual Studio 2022.

Thanks to Simon for raising this issue on 23 November 2022.

In Step 7, I wrote to "select .NET 5.0 (Current)". For this option to appear, you must have installed a version of .NET 5 SDK. If you have only installed .NET 6 then you will only see .NET 6.0 (Long Term Support) as an option.

You have three choices to proceed:

  1. Treat this small section as theory and a reference to how it worked historically. There is no need to perform the steps yourself. I included it to help show the change in behavior between .NET 5 and .NET 6 and to show the code generated by the old template. The rest of the book just uses .NET 6 except for another small section in Chapter 8.
  2. You can install the last version 5.0.408 that was released on May 10, 2022 from the following link: https://dotnet.microsoft.com/en-us/download/dotnet/5.0. .NET 5 has now reached end-of-life which means it is not supported by Microsoft but it still works perfectly well so for learning purposes its fine to use.
  3. You can install .NET 7 SDK from the following link: https://dotnet.microsoft.com/en-us/download/dotnet/7.0. Then when you get to Step 7, in the Additional information dialog, select the check box Do not use top-level statements. This option returns the behavior of the .NET 7 console app template back to similar behavior of .NET 5.

Page 25 - Writing code using Visual Studio Code

In Step 12, I wrote to "create a new console app that targets .NET 5.0". For this option to be available, you must have installed a version of .NET 5 SDK. If you have only installed .NET 6 then you will get an error.

You have three choices to proceed:

  1. Treat this small section as theory and a reference to how it worked historically. There is no need to perform the steps yourself. I included it to help show the change in behavior between .NET 5 and .NET 6 and to show the code generated by the old template. The rest of the book just uses .NET 6 except for another small section in Chapter 8.
  2. You can install the last version 5.0.408 that was released on May 10, 2022 from the following link: https://dotnet.microsoft.com/en-us/download/dotnet/5.0. .NET 5 has now reached end-of-life which means it is not supported by Microsoft but it still works perfectly well so for learning purposes its fine to use.
  3. You can install .NET 7 SDK from the following link: https://dotnet.microsoft.com/en-us/download/dotnet/7.0. Then when you get to Step 12, enter the following command: dotnet new console --use-program-main. This option returns the behavior of the .NET 7 console app template back to similar behavior of .NET 5.

In Step 14, I wrote, "Visual Studio Code may have to download and install C# dependencies like OmniSharp, .NET Core Debugger, and Razor Language Server". This is true up to the most recent release version 1.25.9. But if you install the pre-release version 2.0.x then it does not include OmniSharp any more. To follow the instructions in the book, if you have installed the pre-release version 2.0.x then on the C# extension page, I recommend that you click the button Switch to Release Version to revert back to the current release version 1.25.9.

Downloading and installing C# dependencies will not happen if you do not trust the workspace.

At the top of the window, in the blue bar, click Manage, as shown in the following screenshot:

Restricted mode blue bar

Click the Trust button, as shown in the following screenshot:

Restricted mode

You will then trust the workspace and extensions will activate as described in the book.

A trusted workspace allows extensions to run

Page 28 - Adding a second project using Visual Studio Code

In Step 6, I wrote, "Enter omni, and then, in the drop-down list that appears, select OmniSharp: Select Project."

This works if you installed the most recent release version 1.25.9. But if you installed the pre-release version 2.0.x then it does not include OmniSharp any more.

To follow the instructions in the book, if you have installed the pre-release version 2.0.x then on the C# extension page, I recommend that you click the button Switch to Release Version to revert back to the current release version 1.25.9.

There was also an older issue that has now been resolved with the release of C# extension 1.24.0 on January 20, 2022: https://marketplace.visualstudio.com/items?itemName=ms-dotnettools.csharp

Thanks to johncflorida for raising this issue on 9 December 2021. Also thanks to Paul-Schroeder and ken-from-the-uk who raised the same issue and made suggestions.

In Step 6, I say to select OmniSharp: Select Project. Unfortuately if you have installed version 1.23.17 of the C# extension (released on December 3, 2021) then it gives an error, as shown in the following screenshot and described in these issues:

OmniSharp: Select Project error dialog with version 1.23.17

To avoid the issue, revert back to an earlier version or manually install version v1.24.0-beta1 by downloading the VSIX and then in Visual Studio Code EXTENSIONS, select the Views and More Actions menu (three dots) and then Install from VSIX....

I had hoped that the seriousness of this issue would prompt a non-beta fix by now but the holidays have probably slowed development down. I will leave both issues open and I have added this erratum to warn readers about this temporary issue.

Page 32 - Adding Markdown and special commands to a notebook

Thanks to exzzy22 for raising this issue on January 14, 2022.

In Step 3, I wrote to "click + Markup to add a Markdown cell." I should have written "click + Markdown to add a Markdown cell."

Page 82 - Formatting using interpolated strings

Thanks to GregStevenson for raising this issue on 26 November 2021.

In the last code block in this section, the string is missing the $ prefix that makes it interpolated, as shown in the following code:

private const string fullname = "{firstname} {lastname}";

The code should be as follows:

private const string fullname = $"{firstname} {lastname}";

Page 83 - Understanding format strings

Thanks to dpkwhan for raising this issue on 2 January 2022.

In Step 1, the statement to output the column headings does not need the number format code :N0 because it is a string value, although it does still need the right-alignment format code ,6 to position it within the six character width column.

The following statement:

Console.WriteLine(
  format: "{0,-10} {1,6:N0}",
  arg0: "Name",
  arg1: "Count");

Should be:

Console.WriteLine(
  format: "{0,-10} {1,6}",
  arg0: "Name",
  arg1: "Count");

Page 84 - Getting text input from the user

I wrote that a notebook "does not support reading input from the console using Console.ReadLine()." Although this is true, you can use the Microsoft.DotNet.Interactive.Kernel class and its GetInputAsync method instead. This uses the .NET Interactive integration with the Visual Studio Code user interface to prompt the user for input.

using Microsoft.DotNet.Interactive; // to use the Kernel class

string firstName = await Kernel.GetInputAsync("Type your first name: ");

string age = await Kernel.GetInputAsync("Type your age: ");

Console.WriteLine($"Hello {firstName}, you look good for {age}.");

Getting input from the .NET Interactive kernel

Page 87 - Passing arguments to a console app

Thanks to Bob Molloy for emailing me this issue.

In Step 5, I say, "If you are using Visual Studio, then navigate to Project | Arguments Properties, select the Debug tab, and in the Application arguments box, enter some arguments".

Microsoft changed the user interface of Visual Studio 2022 after that step was written.

It should now say, "If you are using Visual Studio, then navigate to Project | Arguments Properties, select the Debug tab, click Open debug launch profiles UI, and in the Command line arguments box, enter some arguments", as shown in the following screenshot:

Updated UI for setting arguments in Visual Studio 2022

In Figure 2.6, it is difficult to see the hyphen in the second argument in the PDF edition (shown in the screenshot below) and impossible to see it in the Kindle edition.

In Step 5, it would have been clearer if I had written out the arguments as I did in Step 6 instead of relying on Amazon's image processing to clearly show the hyphen!

For example, firstarg second-arg third:arg "fourth arg".

Barely visible hyphen in second-arg

Page 92 - Exercise 2.3 – Practice number sizes and ranges

Thanks to Bob Molloy for emailing me this issue.

In Exercise 2.3, I say, "create a console application project named Exercise02". I should have said, "create a console application project named Exercise03".

Page 111 - Looping with the do statement

Thanks to Norbert Duenki who raised this issue by email on 4 April 2023. Thanks to YachtRocker in the Discord channel for pointing out that I should make the same fix for the 6th edition.

In Step 3, I wrote, "As an optional challenge, add statements so that the user can only make ten attempts before an error message is displayed."

In my code solution in GitHub, I made a mistake in my logic so that if the user entered the correct password on their tenth attempt, it output the error message.

I have updated the logic to fix this issue, as well as to use variables to store the actual password and the maximum number of attempts, as shown in the following code:

// Looping with the do statement

string? actualPassword = "Pa$$w0rd";
string? password;
int maximumAttempts = 10;
int attempts = 0;

do
{
  attempts++;
  Write("Enter your password: ");
  password = ReadLine();
}
while ((password != actualPassword) & (attempts < maximumAttempts));

if (password == actualPassword)
{
  WriteLine("Correct!");
}
else
{
  WriteLine("You have used {0} attempts! The password was {1}.",
    arg0: maximumAttempts, arg1: actualPassword);
}

Page 136 - Converting numbers from cardinal to ordinal

Thanks to Felix Namutare for raising this issue.

The CardinalToOrdinal function fails to properly convert numbers larger than 100 like 111, 112, 113. The fix is to calculate the last two digits and then switch on that value instead, as shown in the following code:

static string CardinalToOrdinal(int number)
{
  int lastTwoDigits = number % 100;

  switch (lastTwoDigits)
  {
    case 11: // special cases from 11th to 13th
    case 12:
    case 13:
      return $"{number}th";
    default:
      int lastDigit = number % 10;

      string suffix = lastDigit switch
      {
        1 => "st",
        2 => "nd",
        3 => "rd",
        _ => "th"
      };
      return $"{number}{suffix}";
  }
}

Page 137 - Calculating factorials with recursion

The factorial function is defined for non-negative integers only i.e. for 0, 1, 2, 3, and so on, and it is defined as:

0!=1 

n!=n×(n−1)!, for n∈{1,2,3,…}

So the implementation of the functions in the book, both for defining the function and for testing it, would be better as shown in the following code:

static int Factorial(int number)
{
  if (number < 0)
  {
     throw new ArgumentException(
       message: $"The factorial function is defined for non-negative integers only. Input: {number}", 
       paramName: nameof(number));
  }
  else if (number == 0)
  {
    return 1;
  }
  else
  {
    checked // for overflow
    {
      return number * Factorial(number - 1);
    }
  }
}


static void RunFactorial()
{
  for (int i = -2; i < 15; i++)
  {
    try
    {
      WriteLine($"{i}! = {Factorial(i):N0}");
    }
    catch (System.OverflowException)
    {
      WriteLine($"{i}! is too big for a 32-bit integer.");
    }
    catch (Exception ex)
    {
      WriteLine($"{ex.GetType()}: {ex.Message}");
    }
  }
}

Page 140 - Documenting functions with XML comments

Thanks to Bob Molloy via email and CoRB-ops for raising this issue on 21 November 2021.

First, it is worth emphasizing that this feature is primarily designed to be used with a tool that converts the comments into documentation like Sandcastle (https://github.com/EWSoftware/SHFB). The tooltips that appear while entering code or hovering over the function name are a secondary feature. Understanding this will help you understand the limitation involved with this errata item.

Second, in Step 4, I say that when calling the function you will see more details. However, when the .NET 6 project templates changed in Preview 7 to use top-level statements and an automatically generated Program class, the functions you write in the tasks became implemented as local functions declared inside the hidden automatically generated <Main>$ method. Local functions do not support XML comments because local functions cannot be used outside the member in which they are declared so it makes no sense to generate documentation from them. Sadly, this also means no tooltip, which would still be useful, but neither Visual Studio 2022 nor Visual Studio Code recognize that.

To enable XML comments for the CardinalToOrdinal function, we must therefore define it inside a class. The easiest way to do this is to add the function to the automatically generated partial Program class by moving the function to the bottom of the Program.cs file and wrapping it in a partial Program class, as shown in the following code:

// This must be at the bottom of the Program.cs file to avoid compile errors.
// Or you could create a separate file, perhaps named Program.CardinalToOrdinal.cs
partial class Program
{
    /// <summary>
    /// Pass a 32-bit integer and it will be converted into its ordinal equivalent.
    /// </summary>
    /// <param name="number">Number is a cardinal value e.g. 1, 2, 3, and so on.</param>
    /// <returns>Number as an ordinal value e.g. 1st, 2nd, 3rd, and so on.</returns>
    static string CardinalToOrdinal(int number)
    {
        switch (number)
        {
            case 11: // special cases for 11th to 13th
            case 12:
            case 13:
                return $"{number}th";
            default:
                int lastDigit = number % 10;
                string suffix = lastDigit switch
                {
                    1 => "st",
                    2 => "nd",
                    3 => "rd",
                    _ => "th"
                };
                return $"{number}{suffix}";
        }
    }
}

Page 159 - Reviewing project packages

If you are having trouble with this section, please read the following two entries from the 7th edition that might be related:

Page 165 - Running unit tests using Visual Studio Code

Thanks to kwatsonkairosmgt for raising this issue on 27 October 2022.

In Step 1, the project name CalculatorLibUnitTest should be CalculatorLibUnitTests.

Page 183 - Importing a namespace to use a type

In Step 3, I wrote a comment with the older C# syntax and a statement with the newer syntax for instantiating a new object, as shown in the following code:

// var bob = new Person(); // C# 1.0 or later
Person bob = new(); // C# 9.0 or later

The var keyword was not introduced until C# 3.0, so I should have written the following:

// Person bob = new Person(); // C# 1.0 or later
// var bob = new Person(); // C# 3.0 or later
Person bob = new(); // C# 9.0 or later

Page 187 - Storing a value using an enum type

Thanks to dpkwhan for raising this issue on 5 January 2022.

In the Good Practice box, the text "If you use are writing code" should be "If you are writing code"

Page 192 - Making a field constant

Thanks to Bob Molloy for emailing me this issue.

In Step 1, the assigned string literal should be "Homo Sapiens". In Step 3, the output should be Bob Smith is a Homo Sapiens.

Page 246 - Releasing unmanaged resources

Thanks to Wuu#0348 on the Discord channel for raising this issue.

In the second bullet point after the large code block, I wrote, "It needs to check the disposing parameter and disposed field because if the finalizer thread has already run and it called the ~Animal method, then only unmanaged resources need to be deallocated." I should have written managed not unmanaged.

It might be clearer if I wrote, "It needs to check the disposing parameter and disposed field because if the finalizer thread has already run and it called the ~Animal method, then unmanaged resources will already have been deallocated and only managed resources remain to be deallocated by the garbage collector." This same typo is in the 7th edition. I will fix this in the 8th edition due to be published in November 2023.

Page 252 - Inheriting from classes

Thanks to Nick Tsiatinis for emailing me this issue.

In Step 3, I wrote, "In Program.cs, ...", but at that point there are now two console app projects with a Program.cs file. I should have said, "In the PeopleApp project, in Program.cs, ..."

Page 260 - Avoiding casting exceptions

Thanks to Nick Tsiatinis for emailing me this issue.

In Step 3, I wrote, "In Main, ...", but there is no Main method. I should have written, "In Program.cs, ..."

Page 292 - Publishing a self-contained app, Page 316 - Exercise 7.3 – Explore PowerShell

In the Good Practice box on page 292, I wrote about how you can automate commands using scripts written in the PowerShell language. My original plan was to write content about PowerShell in the GitHub repository. But PowerShell is a massive topic and there will always be higher priority content to create that is specifically about C# and .NET. In the 8th edition, I will just reference the official PowerShell documentation: https://learn.microsoft.com/en-us/powershell/ And I will remove Exercise 7.3 that suggests exploring PowerShell.

Page 296 - Decompiling using the ILSpy extension for Visual Studio 2022

Thanks to omarz7 for raising this issue on 17 March 2023.

In Step 10, I wrote, "Select the System.IO.FileSystem.dll assembly". This was an unfortunate choice because in the final release version of .NET 6, that assembly's classes use type forwarding and the implementations were moved to the System.Private.Corelib.dll assembly.

In Step 10, it should therefore say, "Select the System.Private.Corelib.dll assembly" instead. The rest of the steps will then work.

In the 7th edition, I changed the instructions to open the System.Linq.dll assembly instead and view the Enumerable.Count method. This is so later in the book the reader will better understand how calling Count can be inefficient because it could require a sequence to be enumerated!

Page 297 - Decompiling using the ILSpy extension for Visual Studio Code

Thanks to Dreamoochy for raising this issue on 24 June 2022.

The ILSpy .NET Decompiler extension for Visual Studio Code has changed behavior. It no longer shows two edit panes side-by-side. Instead, you can only see one language at a time. You can toggle between C# and IL code by clicking the Output language button in the top right corner.

In the next edition, I will tell the reader to open a different assembly so it works with the latest version of ILSpy. Probably the System.Linq assembly and decompile the Enumerable class and its Average method for a sequence of int values:

Note: In the 7th edition I decided to show the Count method instead.

image

And then show how to toggle between C# and IL code by clicking Output language:

image

Page 311 - Understanding the .NET Portability Analyzer

Thanks to Hoshyar Karimi for raising this issue on 28 May 2022.

The link to the demonstration video has changed to: https://docs.microsoft.com/en-us/shows/seth-juarez/brief-look-net-portability-analyzer

Page 316 - Exercise 7.2 – Explore topics

Thanks to Hoshyar Karimi for raising this issue on 28 May 2022.

The link to the chapter links has changed to: https://github.com/markjprice/cs10dotnet6/blob/main/book-links.md#chapter-7---packaging-and-distributing-net-types

Page 384 - Disposing of file resources

Thanks to Dreamoochy for raising this issue on 5 July 2022.

In the finally block, I tell the reader to dispose of the XmlWriter and the FileStream, as shown in the following code:

if (xml != null)
{
  xml.Dispose();
  WriteLine("The XML writer's unmanaged resources have been disposed.");
  if (xmlFileStream != null)
  {
    xmlFileStream.Dispose();
    WriteLine("The file stream's unmanaged resources have been disposed.");
  }
}

But the file stream will only be disposed if the XML writer is successfully created and therefore not null. It would be better to not nest the if statements, as shown in the following code:

if (xml != null)
{
  xml.Dispose();
  WriteLine("The XML writer's unmanaged resources have been disposed.");
}
if (xmlFileStream != null)
{
  xmlFileStream.Dispose();
  WriteLine("The file stream's unmanaged resources have been disposed.");
}

Page 391 - Encoding strings as byte arrays

Thanks to KlarenAlexander for raising this issue on 17 December 2021.

In Step 4, you write code to detect numbers 1 to 5 entered on the keyboard to select between encodings. But the code only accepts numbers entered from the top row of the keyboard. To accept numbers entered on the number pad on an extended keyboard, the code needs to be modified, as shown in the following code:

Encoding encoder = number switch
{
  ConsoleKey.D1 or ConsoleKey.NumPad1 => Encoding.ASCII,
  ConsoleKey.D2 or ConsoleKey.NumPad2 => Encoding.UTF7,
  ConsoleKey.D3 or ConsoleKey.NumPad3 => Encoding.UTF8,
  ConsoleKey.D4 or ConsoleKey.NumPad4 => Encoding.Unicode,
  ConsoleKey.D5 or ConsoleKey.NumPad5 => Encoding.UTF32,
  _                                   => Encoding.Default
};

Page 396 - Serializing as XML

Thanks to Dreamoochy for raising this issue on 6 July 2022.

In Step 8, I show the XML output but I manually formatted it to be easier to read. The output you will see is all on one line.

Page 402 - Controlling JSON processing

Thanks to KlarenAlexander for raising this issue on 17 December 2021.

In Step 5, you write code to configure options for serializing JSON. The code was written in the spring of 2021 when the previews of .NET 6 at the time supported working with the new DateOnly type, although in an inefficient format as shown in the book. Over the summer, the System.Text.Json team added source generator support to improve performance and decided to remove support for DateOnly.

When you run the code in the book with the final release of .NET 6, it throws an, "Unhandled exception. System.NotSupportedException: Serialization and deserialization of 'System.DateOnly' instances are not supported. Path: $.PublishDate."

There is a request to add support for DateOnly and TimeOnly but it seems that we will have to wait for .NET 7 until it is officially supported. Support DateOnly and TimeOnly in JsonSerializer #53539: dotnet/runtime#53539

Meanwhile, we have to implement our own custom JsonConverter classes, like Jørn H. Dalvik (jornhd) suggests in the comments: dotnet/runtime#53539 (comment)

DO NOT USE THIS IN PRODUCTION CODE. Any custom converter implementation that you use is likely to be different from the official implementation so it will break if you serialize data today with your custom implementation and then try to deseralize it later with the official implementation.

I have used Jørn's code to add a new class file to the code solutions that defines converters for DateOnly and DateOnly?, as shown in the following code:

using System.Text.Json;
using System.Text.Json.Serialization;
using System.Text.RegularExpressions;

namespace WorkingWithJson
{
  public class DateOnlyConverter : JsonConverter<DateOnly>
  {
    public override DateOnly Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
      if (reader.TryGetDateTime(out var dt))
      {
        return DateOnly.FromDateTime(dt);
      };
      var value = reader.GetString();
      if (value == null)
      {
        return default;
      }
      var match = new Regex("^(\\d\\d\\d\\d)-(\\d\\d)-(\\d\\d)(T|\\s|\\z)").Match(value);
      return match.Success
          ? new DateOnly(int.Parse(match.Groups[1].Value), int.Parse(match.Groups[2].Value), int.Parse(match.Groups[3].Value))
          : default;
    }

    public override void Write(Utf8JsonWriter writer, DateOnly value, JsonSerializerOptions options)
        => writer.WriteStringValue(value.ToString("yyyy-MM-dd"));
  }

  public class DateOnlyNullableConverter : JsonConverter<DateOnly?>
  {
    public override DateOnly? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
      if (reader.TryGetDateTime(out var dt))
      {
        return DateOnly.FromDateTime(dt);
      };
      var value = reader.GetString();
      if (value == null)
      {
        return default;
      }
      var match = new Regex("^(\\d\\d\\d\\d)-(\\d\\d)-(\\d\\d)(T|\\s|\\z)").Match(value);
      return match.Success
          ? new DateOnly(int.Parse(match.Groups[1].Value), int.Parse(match.Groups[2].Value), int.Parse(match.Groups[3].Value))
          : default;
    }

    public override void Write(Utf8JsonWriter writer, DateOnly? value, JsonSerializerOptions options)
        => writer.WriteStringValue(value?.ToString("yyyy-MM-dd"));
  }
}

Then you must add the DateOnly (and optionally DateOnly?) converters to the JSON options to fix this issue.

// existing code to configure JSON options
JsonSerializerOptions options = new()
{
  IncludeFields = true, // includes all fields
  PropertyNameCaseInsensitive = true,
  WriteIndented = true,
  PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
};

// add converters to enable working with DateOnly and DateOnly?
options.Converters.Add(new DateOnlyConverter());
options.Converters.Add(new DateOnlyNullableConverter());

Page 417 - Database Provider for MySQL

The table shows for MySQL the deprecated NuGet package "MySQL.Data.EntityFrameworkCore". The new one is "MySQL.EntityFrameworkCore"

Page 420 - Defining the Northwind database context class

Thanks to Hoshyar Karimi for raising this issue on 1 June 2022

Thanks to Dylan Sclanders for raising a related issue about losing changes to the database file if you choose to Copy always which will later cause exceptions to be thrown.

After step 7, steps 8 to 10 are only needed for SQLite and its Northwind.db file if you are running the project using Visual Studio 2022.

Step 11 is needed for both SQLite and SQL Server. I should have made that clearer.

For example:

If you are using (a) SQL Server or (b) SQLite with Visual Studio Code

If you are using SQL Server then the data is stored in a database outside the project. It will be found if the connection string is valid for the server name and database name.

If you are using SQLite then the data is stored in a .db database file in the project. If you run the project with Visual Studio Code and the dotnet run command, then the compiled application executes in the WorkingWithEFCore folder. It will be found if the connection string path is valid for the database file.

In both cases:

  1. Run the console application.
  2. Note the output showing which database provider you chose to use.

If you are using SQLite with Visual Studio 2022

If you are using SQLite with Visual Studio 2022, then you need to ensure that the Northwind.db file is in the correct folder. The compiled application executes in the WorkingWithEFCore\bin\Debug\net6.0 folder so it will not find the database file and an exception will be thrown. We need to copy it to the output directory, either only when the database file is newer or each time we run the project:

  1. In Solution Explorer, right-click the Northwind.db file and select Properties.
  2. In Properties, set Copy to Output Directory to Copy if newer.
  3. Run the console application and note the output showing which database provider you chose to use.
  4. Optionally, open WorkingWithEFCore.csproj and note the new elements, as shown in the following markup:
<ItemGroup>
  <None Update="Northwind.db">
    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
  </None>
</ItemGroup>

Note that in the book I say to set it to Copy always but this means that you will lose changes made since the last time you ran the project. For example, later in this exercise, you will write code to add a new product and then update it. If you choose to always copy then when you stop and restart the project you will lose the newly added product and so your code to update it will throw an exception.

Page 428 - Setting up the dotnet-ef tool

Thanks to Nick Tsiatinis for raising this issue on 30 March 2022

If you have an M1 Mac and you choose to install the .NET SDK 6 for Arm64, then beware there is an installer bug that means when you install the dotnet-ef tool, it installs the tool for Intel x64 architecture instead of Arm64. You will not see any problem until you try to run dotnet-ef commands, at which point you see the following error:

A fatal error occurred. The required library libhostfxr.dylib could not be found.
If this is a self-contained application, that library should exist in [/Users/[name]/.dotnet/tools/.store/dotnet-ef/6.0.0/dotnet-ef/6.0.0/tools/netcoreapp3.1/any/].
If this is a framework-dependent application, install the runtime in the global location [/usr/local/share/dotnet/x64] or use the DOTNET_ROOT environment variable to specify the runtime location or register the runtime location in [/etc/dotnet].

To fix this problem:

  1. Uninstall the x86 version using: dotnet tool uninstall --global dotnet-ef.
  2. Force the install of the ARM version using: dotnet tool install --global dotnet-ef -a arm64.

Page 437 - Filtering and sorting products

Thanks to Arendjan Hoek for emailing this issue on 17 August 2022.

In Step 1, I tell you to enter code that queries for products. It checks for a null value and outputs a message to say there were no matches. But if you enter a price like 9999 that should have no matches, the query is empty but it is not null, so no message is output.

The problem is that as far as the compiler knows, the query could return null or a sequence of Product entities (that could be empty). If we attempt to access any member of products, like Count() or Any(), then that would throw a NullReferenceException when products is null. The best approach is therefore to check for both null or "not any", as shown in the following code:

if ((products is null) || (!products.Any()))
{
  WriteLine("No products found.");
  return;
}

Checking for "not any" is more efficient than checking for a count of zero using the following code: (products.Count() == 0).

Note that the order of the clauses in the if statement is important. We must check that products is null first. If it is true, then it will never execute the second clause and therefore it won't throw a NullReferenceException when accessing the Count() member.

Page 438 - Getting the generated SQL

Thanks to Bob Molloy for emailing this issue.

In Step 3, the ORDER BY clause shows the SQL sorts by CategoryId and then by ProductId:

ORDER BY "c"."CategoryId", "t"."ProductId"

The ORDER BY clause should only show the SQL sorts by CategoryId:

ORDER BY "c"."CategoryId"

Page 473 - Targeting a named method

In Step 2, I say "Above the NameLongerThanFour method, pass the method's name into the Func<string, bool> delegate, and then loop through the query items". But earlier, you would already have looped through the items, and you would have modified Jim to Jimmy. So you should comment out the statement that assigns Jimmy, as shown in the following code:

var query = names.Where(
  new Func<string, bool>(NameLongerThanFour));

foreach (string item in query)
{
  WriteLine(item);// outputs Pam
  // names[2] = "Jimmy"; // change Jim to Jimmy
  // on the second iteration Jimmy does not end with an M 
}

Page 509 - Implementing a Recorder class

Thanks to HoshyarKarimi for raising this issue on 5 June 2022.

In Step 1, the implementation of the Stop method includes "elapsed" spelled wrong in the output text:

WriteLine("{0} time span ellapsed.", timer.Elapsed);

WriteLine("{0:N0} total milliseconds ellapsed.",
  timer.ElapsedMilliseconds);

The code should be:

WriteLine("{0} time span elapsed.", timer.Elapsed);

WriteLine("{0:N0} total milliseconds elapsed.",
  timer.ElapsedMilliseconds);

Page 510 - Implementing a Recorder class

Thanks to akrsnr for raising this issue on 30 December 2021.

In Step 3, we see the result of generating an array of 10,000 integers in terms of memory usage. On an M1 Mac you might see a negative value for the physical bytes used, as shown in the following output:

Processing. Please wait...
-1,867,776 physical bytes used.
14,041,088 virtual bytes used.
00:00:06.0042556 time span ellapsed.
6,004 total milliseconds ellapsed.

This could be a bug but I am investigating.

Page 535 - Improving responsiveness for GUI apps

Thanks to Chang-Ping for raising this issue on 27 April 2022.

If you get the error, "The certificate chain was issued by an authority that is not trusted.", then either add the following to the database connection string:

"TrustServerCertificate=True;" +

Or run the following at the command line:

dotnet dev-certs https --trust

Page 562 - Creating a class library for a Northwind database context

In Step 11, you write an extension method that registers the NorthwindContext class for use as a dependency service. In later chapters, this will be used in ASP.NET Core and Blazor projects. By default, a DbContext class is registered using Scope lifetime, meaning that multiple threads can share the same instance. If more than one thread attempts to use the same NorthwindContext class instance at the same time then you will see the following runtime exception thrown:

"A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of a DbContext, however instance members are not guaranteed to be thread safe."

To avoid this, we should register the NorthwindContext class with a Transient lifetime, as shown in the following code:

using Microsoft.EntityFrameworkCore; // UseSqlite
using Microsoft.Extensions.DependencyInjection; // IServiceCollection

namespace Packt.Shared;

public static class NorthwindContextExtensions {
  /// <summary>
  /// Adds NorthwindContext to the specified IServiceCollection. Uses the Sqlite database provider.
  /// </summary>
  /// <param name="services"></param>
  /// <param name="relativePath">Set to override the default of ".."</param>
  /// <param name="databaseFilename">Set to override the default of "Northwind.db"</param>
  /// <returns>An IServiceCollection that can be used to add more services.</returns>
  public static IServiceCollection AddNorthwindContext(
    this IServiceCollection services, 
    string relativePath = "..",
    string databaseFilename = "Northwind.db") {

    string databasePath = Path.Combine(relativePath, databaseFilename);
    
    services.AddDbContext<NorthwindContext>(options => {
      options.UseSqlite($"Data Source={databasePath}");
      options.LogTo(Console.WriteLine,
      new[] { Microsoft.EntityFrameworkCore.Diagnostics.RelationalEventId.CommandExecuting });

    }, 
    // Register with a transient lifetime to avoid concurrency issues in Blazor Server projects.
    contextLifetime: ServiceLifetime.Transient, optionsLifetime: ServiceLifetime.Transient);

    return services;
  }
}

Page 564 - Creating a class library for entity models using SQL Server

In Step 17, you write an extension method that registers the NorthwindContext class for use as a dependency service. In later chapters, this will be used in ASP.NET Core and Blazor projects. By default, a DbContext class is registered using Scope lifetime, meaning that multiple threads can share the same instance. If more than one thread attempts to use the same NorthwindContext class instance at the same time then you will see the following runtime exception thrown:

"A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of a DbContext, however instance members are not guaranteed to be thread safe."

To avoid this, we should register the NorthwindContext class with a Transient lifetime, as shown in the following code:

using Microsoft.EntityFrameworkCore; // UseSqlServer
using Microsoft.Extensions.DependencyInjection; // IServiceCollection

namespace Packt.Shared;

public static class NorthwindContextExtensions {
  /// <summary>
  /// Adds NorthwindContext to the specified IServiceCollection. Uses the SqlServer database provider.
  /// </summary>
  /// <param name="services"></param>
  /// <param name="connectionString">Set to override the default.</param>
  /// <returns>An IServiceCollection that can be used to add more services.</returns>
  public static IServiceCollection AddNorthwindContext(
    this IServiceCollection services,
    string connectionString = "Data Source=.;Initial Catalog=Northwind;" +
     "Integrated Security=true;MultipleActiveResultsets=true;Encrypt=false") {
    
    services.AddDbContext<NorthwindContext>(options => {
      options.UseSqlServer(connectionString);
      options.LogTo(Console.WriteLine,
        new[] { Microsoft.EntityFrameworkCore.Diagnostics.RelationalEventId.CommandExecuting });
    }, 
    // Register with a transient lifetime to avoid concurrency issues Blazor Server projects.
    contextLifetime: ServiceLifetime.Transient, optionsLifetime: ServiceLifetime.Transient);

    return services;
  }
}

Note that I have also written a related improvement here: https://github.com/markjprice/cs11dotnet7/blob/main/docs/errata/improvements.md#page-551---creating-a-class-library-for-entity-models-using-sql-server

Page 597 - Defining a form to insert a new supplier

Thanks to zhangjinshan1990 for raising this issue on May 18, 2024.

In Step 2, you bind HTML three <input> elements to properties of the Supplier class, as shown in the following markup:

<form method="POST">
  <div>
    <input asp-for="Supplier.CompanyName"
            placeholder="Company Name" />
  </div>
  <div>
    <input asp-for="Supplier.Country"
            placeholder="Country" />
  </div>
  <div>
    <input asp-for="Supplier.Phone"
            placeholder="Phone" />
  </div>
  <input type="submit" />
</form>

But you will see three null warnings, as shown in the following output:

Warning (active) CS8602	Dereference of a possibly null reference. Northwind.Web C:\cs10dotnet6\PracticalApps\Northwind.Web\Pages\Suppliers.cshtml 34
Warning (active) CS8602	Dereference of a possibly null reference. Northwind.Web C:\cs10dotnet6\PracticalApps\Northwind.Web\Pages\Suppliers.cshtml 38
Warning (active) CS8602	Dereference of a possibly null reference. Northwind.Web C:\cs10dotnet6\PracticalApps\Northwind.Web\Pages\Suppliers.cshtml 42

To prevent this, in the Razor Page code-behind file, you should make the Supplier property non-nullable (by removing the ? from Supplier?), and then add a statement in the constructor to initialize the Supplier property to a new instance, as shown in the following code:

// Disallow nulls to avoid null warnings in the view.
[BindProperty]
public Supplier Supplier { get; set; }

public SuppliersModel(NorthwindContext db)
{
  _db = db;

  // Initialize the Supplier property to avoid compile error 
  // and potential errors at runtime.
  Supplier = new();
}

Page 645 - Defining a typed view

Thanks to johncflorida for raising this issue.

In Step 3, I say to "add new markup to output categories in a carousel" but the attribute names that I use are for Bootstrap 4 rather than Bootstrap 5 that is included with the ASP.NET Core 6 MVC project template.

In Bootstrap 5, to avoid conflicts with other attribute names:

  • data-ride becomes data-bs-ride
  • data-interval becomes data-bs-interval
  • data-target becomes data-bs-target
  • data-slide-to becomes data-bs-slide-to
  • data-slide becomes data-bs-slide

The four corrected elements are as shown in the following markup:

<div id="categories" class="carousel slide" data-bs-ride="carousel"
     data-bs-interval="3000" data-keyboard="true">
<li data-bs-target="#categories" data-bs-slide-to="@c" 
    class="@currentItem"></li>
<a class="carousel-control-prev" href="#categories"
   role="button" data-bs-slide="prev">
<a class="carousel-control-next" href="#categories"
   role="button" data-bs-slide="next">

Page 688 - Controlling XML serialization

In Step 4, I say, "In the Northwind.Common.EntityModels.SqlServer project, decorate the CustomerCustomerDemos property with [XmlIgnore] too."

This should say, "In the Northwind.Common.EntityModels.SqlServer project, in Customers.cs, decorate the CustomerTypes property with [XmlIgnore] too."

Page 701 - Enabling HTTP logging

Thanks to Nick Tsiatinis for raising this issue on 27 April 2022.

The book misses an important step to enable HTTP logging. You must configure the level of ASP.NET Core logging to Information because it usually is configured as Warning and therefore does not output.

  1. Open appsettings.Development.json.
  2. Add an entry or modify the log level of Microsoft.AspNetCore to Information:
{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.AspNetCore": "Information",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  }
}

Note: Although the Default log level might be set to Information, more specific configurations take priority. For example, any logging systems in the Microsoft namespace will use Warning level. Any logging systems in the Microsoft.AspNetCore namespace will now use Information.

Page 703 - Configuring HTTP clients using HttpClientFactory

Thanks to Nick Tsiatinis for raising this issue on 27 April 2022.

In Step 1, I tell you to configure the Web API service to use port 5002 by calling the UseUrls method, as shown in the following code:

builder.WebHost.UseUrls("https://localhost:5002/");

But there is a bug in .NET 6 that causes it to ignore this configuration and continue to use the configuration in the launchSettings.json file, as explained at the following link: dotnet/aspnetcore#38185

To fix this, modify applicationUrl setting in the launchSettings.json file, as shown in the following configuration:

"profiles": {
    "Northwind.WebApi": {
      "commandName": "Project",
      "dotnetRunMessages": true,
      "launchBrowser": false,
      "launchUrl": "swagger",
      "applicationUrl": "https://localhost:5002",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    },

Page 706 - Enabling Cross-Origin Resource Sharing

Thanks to Dreamoochy for raising this issue on 3 August 2022.

In Step 3, I say, "Add a statement in the HTTP pipeline configuration section, before calling UseEndpoints, to use CORS" but there is no call to UseEndpoints.

Add the code immediately after the app object is built, as shown in the following code:

var app = builder.Build();

// Configure the HTTP request pipeline.

app.UseCors(configurePolicy: options =>
{
  options.WithMethods("GET", "POST", "PUT", "DELETE");
  options.WithOrigins(
    "https://localhost:5001" // allow requests from the MVC client
  );
});

In Step 4, I say, "Start the Northwind.WebApi project and confirm that the web service is listening only on port 5002." In the next edition I will add that if you are using Visual Studio then you should start it without debugging.

Good Practice: Always start your Visual Studio 2022 projects without debugging unless you are actually debugging. This is for two good reasons. First, starting a project with the debugger attached is much slower, and second, it prevents that copy of Visual Studio from starting another project at the same time. If you start a project without the debugger attached then you can use that single copy of Visual Studio to start as many projects as you need.

Page 708 - Implementing a Health Check API

In Step 8, I say to note the SQL statement that is executed to check the health of the service. This behavior was removed late in the process. To add it back, you can install the following package to your Northwind.WebApi project file:

<PackageReference Include="AspNetCore.HealthChecks.SqlServer" Version="6.0.2" />

And then in your Program.cs file, in the section for configuring services, add a call to the AddSqlServer method to use it:

builder.Services.AddHealthChecks()
  .AddDbContextCheck<NorthwindContext>()
  // execute SELECT 1 using the specified connection string
  .AddSqlServer("Data Source=.;Initial Catalog=Northwind;Integrated Security=true;");

Warning! The AspNetCore.HealthChecks.SqlServer is not officially supported by Microsoft.

Page 712 - Building a weather service using minimal APIs

Thanks to Nick Tsiatinis for raising this issue on 27 April 2022.

In Step 1, I tell you to configure the Minimal Web API service to use port 5003 by calling the UseUrls method, as shown in the following code:

builder.WebHost.UseUrls("https://localhost:5003/");

But there is a bug in .NET 6 that causes it to ignore this configuration and continue to use the configuration in the launchSettings.json file, as explained at the following link: dotnet/aspnetcore#38185

To fix this, modify applicationUrl setting in the launchSettings.json file, as shown in the following configuration:

"profiles": {
    "Minimal.WebApi": {
      "commandName": "Project",
      "dotnetRunMessages": true,
      "launchBrowser": true,
      "launchUrl": "api/weather",
      "applicationUrl": "https://localhost:5003",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    },

Bonus Content: Chapters 18 to 20 and Appendix

Page 20 - Adding a services page to the Northwind MVC website

Thanks to Dreamoochy for raising this issue on 11 August 2022.

In Step 3, I say to "add a new empty view named Services.cshtml and modify its contents to render the products". The code uses the older Bootstrap 4 class names of badge badge-info but it should use the newer Bootstrap 5 classes named of badge bg-info, as shown in the following markup:

<h2>Products that start with Cha using OData</h2>
  <p>
  @if (products is null)
  {
    <span class="badge bg-info">No products found.</span>
  }
  else
  {
    @foreach (Product p in products)
   {
     <span class="badge bg-info">
       @p.ProductId 
       @p.ProductName

Page 35 - Building a client for GraphQL

In Step 5, I say to "render the Seafood products". The code uses the older Bootstrap 4 class names of badge badge-success but it should use the newer Bootstrap 5 classes named of badge bg-success, as shown in the following markup:

<h2>Seafood products using GraphQL</h2>
<p>
  @foreach (Product p in seafoodProducts)
  {
    <span class="badge bg-success">
      @p.ProductId
      @p.ProductName
      -
      @(p.UnitsInStock is null ? "0" : p.UnitsInStock.Value) in stock
    </span>
  }
</p>

Page 41 - Testing a gRPC client to the gRPC service

In Step 8, I say to "View the command prompt or terminal for the gRPC service and note the info messages" but you will only see this output if you have enabled Info level logging as described in Page 703 - Configuring HTTP clients using HttpClientFactory.

Page 141 - Appendix A - Exercise 3.1 – Test your knowledge

Thanks to zeier for raising this issue on 1 December 2021.

Question 6 asked, "What are the three parts of a for statement and which of them are required?"

Answer: The three parts of a for statement are the initializer, condition, and incrementer expressions. The condition expression is required to evaluate to true or false, but the other two are optional.

But the conditional expression is NOT required to evaluate to true or false. Like the other two parts, it is optional. If it is missing then the for statement will loop forever.

Question 8 asked, "Does the following statement compile? for ( ; true; ) ;"

For the same reasons, the description in the answer should read, "Yes. The for statement does not require any of the three parts to be defined. The initializer, condition, and incrementer expressions are optional. Even if the true value was missing, this for statement will execute the empty ; statement after the close brace, forever. It is an example of an infinite loop."

Page 143 - Appendix A - Exercise 4.1 – Test your knowledge

Thanks to jbeale1 John Beale for raising this issue on 3 January 2022.

Question 3 asked, "In Visual Studio Code or Visual Studio, what is the difference between pressing F5, Ctrl or Cmd + F5, Shift + F5, and Ctrl or Cmd + Shift + F5?"

The answer included a typo: the word "with" instead of the correct "without", as shown in the following text:

Answer: F5 saves, compiles, runs, and attaches the debugger; Ctrl or Cmd + F5 saves, compiles, and runs the application without the debugger attached; Shift + F5 stops the debugger and running application; and Ctrl or Cmd + Shift + F5 restarts the application without the debugger attached.