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Errata (53 items)

If you find any mistakes, then please raise an issue in this repository or email me at markjprice (at) gmail.com.

Page 5 - Choosing the appropriate tool and application type for learning

Thanks to s3ba-b for raising this issue on November 3, 2024.

The last sentence says, "Then, in Chapters 12 to 16, you will build websites, services, and web browser apps." It should have said, "Then, in Chapters 12 to 15, you will build websites, web browser apps, and web services."

Page 10 - Installing other extensions

Thanks to Muhammad Faisal Siddiqui for raising this issue on November 20, 2023.

At the time of publishing, the Polyglot Notebooks extension has a dependency on .NET 7. The extension will soon be updated to use .NET 8 but for now you must install .NET 7 SDK. Hopefully the team will also update the extension to use the .NET Install Tool that ensures a correct version of a required .NET SDK is installed so users do not have to manually install it.

Note: The .NET Interactive team targetted .NET 8 two days after this issue was raised: dotnet/interactive#3336.

Support for LTS only: When .NET 9 is released in November 2024, Interactive .NET and Polyglot Notebooks will upgrade to it. If you are limited to only LTS releases, "As a workaround, you can install older versions of Polyglot Notebooks that use previous .NET versions and turn off automatic updates in VS Code.": dotnet/interactive#3355.

Page 15 - Understanding .NET runtime and .NET SDK versions

Thanks to a reader who contacted my publisher Packt on November 16, 2023 about this issue.

I wrote, ".NET SDK versioning does not follow semantic versioning. The major and minor version numbers are tied to the runtime version it is matched with. The patch number follows a convention that indicates the major and minor versions of the SDK."

But the patch number is not created from the major and minor versions of the SDK. It is created from the minor and patch versions of the SDK.

I should have written, ".NET SDK versioning does not follow semantic versioning. The major and minor version numbers are tied to the runtime version it is matched with. The third number follows a convention that indicates the minor and patch versions of the SDK. The third number starts at 100 for the initial version (equivalent to 0.0 for minor and patch number). The first digit increments with minor increments, and the other two digits increment with patch increments."

Page 43 - Configuring inline aka inlay hints

Thanks to TheFumblebee for raising this issue on November 30, 2023.

In the bullet for Visual Studio 2022, I wrote the label for the check box was Display inline parameter hint names. I should have written Display inline parameter name hints.

Page 50 - Exercise 1.2 – Practice C# anywhere with a browser

Thanks to MrBiteyFace in the book's Discord channel for raising this issue.

In this exercise, I wrote "You can start coding online at any of the following links: Visual Studio Code for Web: https://vscode.dev/".

Although Visual Studio Code for Web does support some extensions, it does not support the C# extension. If you edit a .cs file then you will not have IntelliSense to help you. It also does not support running and debugging C# code.

In the next edition, I will remove this bullet or change it to GitHub Codespaces (i.e. Visual Studio Code hosted in a cloud-based virtual machine) instead.

Page 51 - Exercise 1.5 – Explore themes of modern .NET

Thanks to Emre Duman who raised this issue on March 11, 2024.

Microsoft appears to have stopped paying for the domain used by the following link: https://themesof.net/. In the next edition, I will remove this exercise.

Page 54 - Understanding C# standards

Thanks to mark23344 who raised this issue on May 10, 2024.

In the note box, I put a link to the C# specifications: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/specifications. But Microsoft changed the link without an automatic redirect so that link now returns a 404.

The new link is: https://learn.microsoft.com/en-us/dotnet/csharp/specification/.

Page 58 - Showing the compiler version

In Step 3, the code should have been styled as Code (monospace black-on-light-gray text) instead of Command Line (monospace white-on-black).

Page 65 - Comparing programming languages to human languages

Thanks to zaynchoudry who raised this issue on April 14, 2024.

I wrote, "this YouTube video shows a demonstration of an Arabic programming language: https://youtu.be/dkO8cdwf6v8."

That video has been removed. An alternative is available at the following link: https://www.youtube.com/watch?v=EwYIZBL4sAU.

Page 87 - Comparing double and decimal types

Thanks to Yousef Imran who raised this issue via email on December 15, 2023.

At the top of page 87, I end the section describing a few special values associated with real numbers that are available as constants in the float and double types. I wrote, "NaN represents not-a-number (for example, the result of dividing by zero)," but that sentence is missing a "zero". It should be, "NaN represents not-a-number (for example, the result of dividing zero by zero),". In the next edition I will fix this mistake.

Please also note a related improvement.

Page 95 - Displaying output to the user

Thanks to SilentSolace in the book's Discord channel for raising this issue on December 18, 2023.

I wrote, "If you want to write three letters to the console without carriage returns after them, then call the Write method, as shown in the following code:"

Write("A");
Write("B");
Write("C");

But I neglected to prefix the method calls with Console. so how does this work?

On page 102, in the section titled "Simplifying the usage of the console", I show how to avoid needing to prefix those method calls with Console. by adding a statement to statically import the System.Console class, as shown in the following code:

using static System.Console;

But seven pages earlier I show code without the prefix without an explanation why that works!

In the next edition, I will show the full code, as shown in the following code:

Console.Write("A");
Console.Write("B");
Console.Write("C");

And the same for the second code block:

Console.WriteLine("A");
Console.WriteLine("B");
Console.WriteLine("C");

Page 110 - Handling platforms that do not support an API

Thanks to rmantel23 for raising this issue on June 4, 2024.

At the top of page 110, I wrote, "Another way to handle differences in operating systems is to use the OperatingSystem class in the System namespace, as shown in the following code:"

if (OperatingSystem.IsWindows())
{
  // Execute code that only works on Windows.
}
else if (OperatingSystem.IsWindowsVersionAtLeast(major: 10))
{
  // Execute code that only works on Windows 10 or later.
}
else if (OperatingSystem.IsIOSVersionAtLeast(major: 14, minor: 5))
{
  // Execute code that only works on iOS 14.5 or later.
}
else if (OperatingSystem.IsBrowser())
{
  // Execute code that only works in the browser with Blazor.
}

But the if (OperatingSystem.IsWindows()) branch will always execute if the OS is Windows, and therefore the else if (OperatingSystem.IsWindowsVersionAtLeast(major: 10)) branch will never execute!

In the next edition I will fix the logic error, as shown in the following code:

if (OperatingSystem.IsWindowsVersionAtLeast(major: 10))
{
  // Execute code that only works on Windows 10 or later.
}
else if (OperatingSystem.IsWindows())
{
  // Execute code that only works on earlier versions of Windows.
}
else if (OperatingSystem.IsIOSVersionAtLeast(major: 14, minor: 5))
{
  // Execute code that only works on iOS 14.5 or later.
}
else if (OperatingSystem.IsBrowser())
{
  // Execute code that only works in the browser with Blazor.
}

Page 124 - Exploring bitwise and binary shift operators

Thanks to Vlad Alexandru Meici for raising this issue on January 19, 2024.

In Step 3, I refer to variables a and b, "In Program.cs, add statements to output the results of applying the left-shift operator to move the bits of the variable a by three columns, multiplying a by 8, and right-shifting the bits of the variable b by one column, ...".

I should have written x and y.

In the last paragraph, I wrote, "The 3 result is because the 1 bits in b were shifted one column into the 2-and 1-bit columns."

I should have written, "The 3 result is because the 1 bits in y were shifted one column into the 2-and 1-bit columns."

Page 149 - How negative numbers are represented in binary

Thanks to Mahmoud Elnagar for raising this issue on May 26, 2024.

In Step 3, I wrote, "Note that all the positive binary number representations start with 0 and all the negative binary number representations start with 1. The decimal value -1 is represented by all ones in binary. That is why when you have an integer too large to fit in a 32-bit integer, it becomes -1."

As Mahmoud says, it's not always the case that the result of this type of casting is -1. When casting from a wider integer data type to a narrower integer data type, the most significant extra bits gets truncated and the least significant bits represents the result of the casting. For example:

long x = 0b_101000101010001100100111010100101010;
int y = (int) x;

Console.WriteLine($"{x,38:B38} = {x}");
Console.WriteLine($"{y,38:B32} = {y}");

The result:

00101000101010001100100111010100101010 = 43657622826
      00101010001100100111010100101010 = 707949866

Page 162 - Throwing overflow exceptions with the checked statement

Thanks to Justin Treher for raising this issue on January 3, 2025.

In Step 3, I wrote, "let’s get the compiler to warn us about the overflow by wrapping the statements using a checked statement block", but it is not the compiler that warns us, it is the runtime that detects the overflow and throws the exception. In the next edition I will replace "compiler" with "runtime".

Page 225 - Where to catch exceptions

Thanks to Michael Smith for emailing me about this typo on May 22, 2024.

I wrote, "You might know that calling an exception could throw one or more types of exception, ..."

It should be, "You might know that calling a function could throw one or more types of exception, ..."

Page 241 - Inheriting from System.Object

Thanks to Emre Duman for raising this issue on June 21, 2024.

I wrote, "note that the class is in a .NET Standard 2.0 class library assembly and has a method named ToString, as shown in Figure 5.1:" but the screenshot cannot show the ToString method because it is too far down the class code file.

In the next edition, I will remove the text, "and has a method named ToString". After the figure, I will add a paragraph, "If you scroll down the class code file, note that the Object class has a method named ToString."

Page 261 - Passing optional parameters

Thanks to Vlad Alexandru Meici for raising this issue on March 18, 2024.

In Step 1, the method signature has an extra space between command and =, as shown in the following code:

public string OptionalParameters(string command  = "Run!",

Although extra whitespace has no effect on the compiler, in the next edition, I will remove the extra space, as shown in the following code:

public string OptionalParameters(string command = "Run!",

Page 265 - Controlling how parameters are passed

Thanks to Stanislav Svystovych for raising this issue on June 4, 2024.

In Step 4, I wrote, "In Program.cs, add statements to declare some more variables, including an out parameter named f declared inline, ..."

The variable name is h not f, so this should be, "In Program.cs, add statements to declare some more variables, including an out parameter named h declared inline, ..."

Page 295 - Setting up a class library and console application

Thanks to rmantel23 for raising this issue on June 14, 2024.

In Step 6, I defined a region for properties and meant to define three properties, but although the first two members are properties, the third is missing its getter and setter, as shown in the following code:

public List<Person> Children = new();

It should be as follows:

public List<Person> Children { get; set; } = new();

Page 296 - Implementing functionality using methods

Thanks to rmantel23 for raising this issue on June 14, 2024.

In Step 1, I wrote "add properties", but I defined a field, as shown in the following code:

public List<Person> Spouses = new();

It should be as follows:

public List<Person> Spouses { get; set; } = new();

Page 305 - Working with non-generic types

Thanks to rmantel23 for raising this issue on June 14, 2024.

After the four steps, I wrote a paragraph, "Although the code works, there is potential for mistakes because literally any type can be used for the key or value. If another developer used your variable named and expected all the items to be a certain type, ..."

In the second sentence, I failed to name the variable. The sentence should be: "If another developer used your variable named lookupObject and expected all the items to be a certain type, ..." Or I might just delete the word "named". Either would make the sentence less confusing.

Page 316 - Comparing objects when sorting

Thanks to Obs in the Discord channel for this book for raising this issue on October 10, 2024.

In Step 5, I wrote, "In Person.cs, after inheriting from object, add a comma and enter IComparable<Person?>, as highlighted in the following code:

public class Person : IComparable<Person?>

That instruction was written for an earlier edition where the Person class explicitly inherited from object. For example, Person : object.

In the next edition, I will change Step 5 to be, "In Person.cs, add code to say that Person implements the IComparable<Person?> interface, ..."

Thanks to Ashish in the Discord channel for this book for raising this issue.

In Step 9, the final else statement will never execute because the logic of the if and else if clauses mean it will only execute when this (the current object instance) is null. In that scenario, the method could not execute anyway since the object wouldn't exist! When I wrote the if statement, I exhaustively covered all combinations of null and not null for other and this, but one of those combinations could never in practice happen.

In the next edition, I will add a comment for the following code from the CompareTo method:

else
{
  position = 0; // this and other are at same position.
}

And I will add a comment in the code explaining why it is not needed. I have already done this in the code solution here: https://github.com/markjprice/cs12dotnet8/blob/main/code/Chapter06/PacktLibrary/Person.cs#L196

Page 324 - How reference and value types are stored in memory

Thanks to rmantel23 for raising this issue on June 17, 2024.

In the code, I used TimeSpace.Zero. It should be TimeSpan.Zero.

Page 324 - How reference and value types are stored in memory

Thanks to Steven Wu for raising this issue on January 5, 2025.

In the code, I used System.Drawing.Point location = new(x: 4, y: 5);.

It should be System.Drawing.Point location = new(x: 3, y: 5); to match Figure 6.1 (or the figure could be changed to match the code).

Page 331 - Defining record struct types

Thanks to Vlad Alexandru Meici for raising this issue on November 23, 2024.

In Step 1, I wrote, "In the DisplacementVector type, add the record keyword, as highlighted in the following code:"

public record struct DisplacementVector(int X, int Y);

The statement should not end with (int X, int Y); Although this syntax is correct, there is a lot more code in the type as currently defined. That statement should be:

public record struct DisplacementVector

Page 344 - Inheriting from classes

Thanks to rmantel23 for raising this issue on June 18, 2024.

In Step 3, the following code statment includes an extra close-parenthesis: TimeSpan.Zero)). It should be: TimeSpan.Zero).

The code was already correct in the GitHub repository, as shown in the following code: https://github.com/markjprice/cs12dotnet8/blob/main/code/Chapter06/PeopleApp/Program.cs#L191

Page 361 - Comparing inheritance and implementation

Thanks to Blix in this book's Discord channel for pointing out this typo.

For the first sentence, I wrote, "For me, the terms inherit and implement are different, and in the early days of C# and .NET you could strictly apply them to classes and interfaces respectfully."

In the next edition, I will correct the word "respectfully" to "respectively", as explained at the following link: https://www.merriam-webster.com/grammar/respectively-vs-respectfully.

Page 375 - Revealing the location of a type

Thanks to rmantel23 for raising this issue on June 20, 2024.

In Step 1, I wrote, "In the search box, enter navigation in source." This should be, "In the search box, enter navigation to source." to match the check box label so it gets highlighted in the user interface.

Page 383 - Creating a console app to publish

Thanks to mdj._ in the book's Discord channel for raising this issue on December 18, 2023.

In Step 5, I tell the reader to "add the runtime identifiers (RIDs) to target five operating systems" including Windows 10 or later. The legacy RID was win10-x64 but in .NET 8 RC1 this changed to win-x64. The RID for MacOS/OS X also changed. From the documentation, "Starting with .NET 8, the default behavior of the .NET SDK and runtime is to only consider non-version-specific and non-distro-specific RIDs."

The book lists the RIDs as shown in the following markup:

<RuntimeIdentifiers>
  win10-x64;osx-x64;osx.11.0-arm64;linux-x64;linux-arm64
</RuntimeIdentifiers>

The RIDs should be as shown in the following markup:

<RuntimeIdentifiers>
  win-x64;osx-x64;osx-arm64;linux-x64;linux-arm64
</RuntimeIdentifiers>

In the next edition, as well as fixing the RID values, I will link to the official documentation so that readers can confirm the current valid values. For example, for known RIDs: https://learn.microsoft.com/en-us/dotnet/core/rid-catalog#known-rids.

Page 386 - Publishing a self-contained app

Thanks to mdj._ in the book's Discord channel for raising this issue on December 18, 2023.

Related to the previous issue, in Step 2, I tell the reader to "Enter a command to build and publish the self-contained release version of the console application for Windows 10". But the command uses the legacy RID value win10-x64, as shown in the following command:

dotnet publish -c Release -r win10-x64 --self-contained

The command should be:

dotnet publish -c Release -r win-x64 --self-contained

Any other references to win10-x64, like the folder name, should also be changed to win-x64.

Similarly, in Step 4, the command dotnet publish -c Release -r osx.11.0-arm64 --self-contained should be:

dotnet publish -c Release -r osx-arm64 --self-contained

I have updated the Command Lines summary file to use the new valid RIDs: https://github.com/markjprice/cs12dotnet8/blob/main/docs/command-lines.md#page-386---publishing-a-self-contained-app

Page 388 - Publishing a single-file app

Thanks to Vlad Alexandru Meici for raising this issue on December 8, 2024.

In the two command lines, I used /p to set a project property when I should have used -p. The complete command is:

dotnet publish -r win10-x64 -c Release --no-self-contained -p:PublishSingleFile=true

Page 394 - Publishing a native AOT project

Thanks to Nathan Wolfe for raising this issue on January 14, 2025.

I wrote, "A console app that functions correctly during development when the code is untrimmed and JIT-compiled could still fail once you publish it using native AOT because then the code is trimmed and JIT-compiled and, therefore, it is a different code with different behavior."

But I mistakenly repeated "JIT-compiled" when I meant "AOT-compiled".

I should have written, "A console app that functions correctly during development when the code is untrimmed and JIT-compiled could still fail once you publish it using native AOT because then the code is trimmed and AOT-compiled and, therefore, it is a different code with different behavior."

Page 399 - Decompiling using the ILSpy extension for Visual Studio 2022

Thanks to rene in the book's Discord channel for raising this issue.

At the end of the Good Practice box, I wrote, "What it doesn’t do is check if the sequence is an array and then use the Length property. If you have an array of any type, avoid Count() in favor of the Length property."

The System.Array class implements ICollection, and in particular it implements its Count property by returning the Length property. In the next edition, I have replaced those two incorrect sentences with corrected information, as shown at the following link:

https://github.com/markjprice/cs13net9/blob/main/docs/ch07-decompiling.md#decompiling-using-the-ilspy-extension-for-visual-studio

Page 400 - Viewing source links with Visual Studio 2022

Thanks to rmantel23 for raising this issue on June 20, 2024.

In Step 1, I wrote, "In the search box, enter navigation in source." This should be, "In the search box, enter navigation to source." to match the check box label so it gets highlighted in the user interface.

Page 421 - Generating GUIDs

Thanks to Cem Kaya for raising this issue on March 20, 2024.

In Step 1, I wrote, "In Program.cs, add statements to access the shared Random instance, and then call its methods to generate random numbers, as shown in the following code:"

This should have been, "In Program.cs, add statements to output the value of an empty Guid, generate a new random Guid and then output its value, and finally output each individual byte of the random Guid value, as shown in the following code:".

Page 430 - Regular expression performance improvements

Thanks to rmantel23 for raising this issue on July 11, 2024.

I wrote, "The .NET types for working with regular expressions are used throughout the .NET platform and many of the apps built with it. As such, they have a significant impact on performance. But until now, they have not received much optimization attention from Microsoft."

The last sentence was written for an earlier edition and not updated. In the next edition, I will update it to say, "But until .NET 5, they had not received much optimization attention from Microsoft."

Page 430 - Understanding the syntax of a regular expression

Thanks to rene in the book's Discord channel for raising this issue.

In Table 8.6, the entry for {,3} is wrong. That is not a valid range and so it actually matches the exact string {,3}! To match "Up to three", you should use {0,3} or {1,3} depending on whether you want to accept zero or one as the lowest value. I will fix this in the 10th edition.

Page 468 - Managing directories, Managing files

Thanks to Vlad Alexandru Meici for raising this issue on December 31, 2024.

After prompting the user to press any key to delete the directory or file, the code should have an extra statement to output a new line otherwise the next text written to the console will appear immediately at the end of the "Press any key..." text.

This has been fixed in the code solutions here: https://github.com/markjprice/cs12dotnet8/commit/81edf105ad5ae9a18bec32abe4b07342805e95bc

Page 509 - Expanding, setting, and getting an environment variables

Thanks to rene in the book's Discord channel for raising this issue on January 13, 2025.

In Step 5, I wrote, "get an environment variable named MY_PASSWORD at all three potential scope levels". But the environment variable is named MY_SECRET.

Also, it would be more logical to order the reading of the environment variables: process, user, and then machine, as shown in the following code:

string secret_key = "MY_SECRET";

string? secret = GetEnvironmentVariable(secret_key,
  EnvironmentVariableTarget.Process);
WriteLine($"Process - {secret_key}: {secret}");

secret = GetEnvironmentVariable(secret_key,
  EnvironmentVariableTarget.User);
WriteLine($"User -    {secret_key}: {secret}");

secret = GetEnvironmentVariable(secret_key,
  EnvironmentVariableTarget.Machine);
WriteLine($"Machine - {secret_key}: {secret}");

Now the environment variables are rendered in alphabetical order, as shown in the following output:

Process - MY_SECRET: Alpha
User -    MY_SECRET: Beta
Machine - MY_SECRET: Gamma

Page 522 - Using the lightweight ADO.NET database providers

Thanks to blix11 in the book's Discord channel for raising this issue.

In the fourth paragraph I wrote, "The EF Core database providers for SQLite and SQL Server are built on top of the ADO.NET libraries, so EF Core is always inherently slower than ADO.NET. Furthermore, ADO.NET can be used independently for better performance because the EF Core database providers are “closer to the metal.”"

The second sentence is confusing or just wrong, and I probably meant to write, "Furthermore, ADO.NET can be used independently which will give better performance because the ADO.NET database providers are “closer to the metal.”". But even then the sentence doesn't add much so in the next edition I will remove that sentence.

Page 538 - Scaffolding models using an existing database

Thanks to rmantel23 for raising this issue on September 4, 2024.

In the fourth bullet for the notes about the code, I wrote, "The CategoryId property is decorated with the [Key] attribute to indicate that it is the primary key for this entity. The data type for this property is int for SQL Server and long for SQLite. We did not do this because we followed the naming primary key convention."

The second sentence is the wrong way round. It should say, "The data type for this property is int for SQLite and long for SQL Server." I will fix this in the next edition.

Page 548 - Getting the generated SQL

Thanks to Ashish in the book's Discord channel for raising this issue.

In Step 1, I wrote, "In the FilteredIncludes method" and in the GitHub solution code I do the same thing. Originally this was so that later you could see what happens when you run that method. But I'm not sure if this is necessary now because in the next section I get the reader to enable logging of SQL queries globally. It's also confusing because it happens to use a variable named categories so a reader might think I meant to add the statement to the QueryCategories method but this is not necessary. For the next edition, I might just remove this step.

In Step 3, I wrote, "Run the code, enter a minimum value for units in stock, like 99, and view the result," but the output shows I entered 95. In the next edition I will change the text to also say 95.

Page 553 - Getting a single entity

Thanks to Ashish in the book's Discord channel for raising this issue.

In Step 3, I show output of the logged SQL which includes WHERE NOT ("p"."Discontinued") AND "p"."ProductId" > @__id_0. But I do not tell the reader to add a global filter that would add the NOT ("p"."Discontinued") clause to the WHERE until the Defining global filters section on page 557.

In the next edition, I will edit the output to remove this SQL clause, as shown in the following output:

Enter a product ID: 1
Connection: Data Source=C:\cs12dotnet8\Chapter10\WorkingWithEFCore\bin\
Debug\net8.0\Northwind.db
dbug: 9/17/2023 18:04:14.210 RelationalEventId.CommandExecuting[20100]
(Microsoft.EntityFrameworkCore.Database.Command)
    Executing DbCommand [Parameters=[@__id_0='1'], CommandType='Text',
CommandTimeout='30']
    SELECT "p"."ProductId", "p"."CategoryId", "p"."UnitPrice",
"p"."Discontinued", "p"."ProductName", "p"."UnitsInStock"
    FROM "Products" AS "p"
    WHERE "p"."ProductId" > @__id_0
    LIMIT 1
Info > First: Chang
dbug: 9/17/2023 18:04:14.286 RelationalEventId.CommandExecuting[20100]
(Microsoft.EntityFrameworkCore.Database.Command)
    Executing DbCommand [Parameters=[@__id_0='1'], CommandType='Text',
CommandTimeout='30']
    SELECT "p"."ProductId", "p"."CategoryId", "p"."UnitPrice",
"p"."Discontinued", "p"."ProductName", "p"."UnitsInStock"
    FROM "Products" AS "p"
    WHERE "p"."ProductId" > @__id_0
    LIMIT 2
Info > Single: Chang

Page 616 - Be careful with Count!

Thanks to Clint Mayers who submitted this issue via email.

I showed a code teaser by Amichai Mantinband, a software engineer at Microsoft, as shown in the following code:

IEnumerable<Task> tasks = Enumerable.Range(0, 2)
  .Select(_ => Task.Run(() => Console.WriteLine("*")));

await Task.WhenAll(tasks);
Console.WriteLine($"{tasks.Count()} stars!");

But I mistakenly used WriteLine methods when they should have been Write methods, as shown in the following code:

IEnumerable<Task> tasks = Enumerable.Range(0, 2)
  .Select(_ => Task.Run(() => Console.Write("*")));

await Task.WhenAll(tasks);
Console.Write($"{tasks.Count()} stars!");

Page 641 - Customizing the model and defining an extension method

Thanks to swissbobo in the book's Discord channel for raising this issue.

In Step 4, in the AddNorthwindContext method, Word's autocorrect changed an o into an O in Options.UseSqlite, as shown in the following code:

services.AddDbContext<NorthwindContext>(options =>
{
  // Data Source is the modern equivalent of Filename.
  Options.UseSqlite($"Data Source={path}");

  options.LogTo(NorthwindContextLogger.WriteLine,
    new[] { Microsoft.EntityFrameworkCore
      .Diagnostics.RelationalEventId.CommandExecuting });
}

The correct code is shown here:

services.AddDbContext<NorthwindContext>(options =>
{
  // Data Source is the modern equivalent of Filename.
  options.UseSqlite($"Data Source={path}");

  options.LogTo(NorthwindContextLogger.WriteLine,
    new[] { Microsoft.EntityFrameworkCore
      .Diagnostics.RelationalEventId.CommandExecuting });
}

This is only a problem in the source code in the print book and PDF, not in the GitHub repository, as shown in the following statement:

cs12dotnet8/code/PracticalApps/Northwind.DataContext.Sqlite/NorthwindContextExtensions.cs

Line 33 in de8310d

options.UseSqlite($"Data Source={path}");

Page 684 - Defining a form to insert a new supplier

Thanks to zhangjinshan1990 for raising this issue on May 18, 2024 in the C# 10 and .NET 6 repository.

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

Warning (active) CS8602	Dereference of a possibly null reference. Northwind.Web C:\cs12dotnet8\PracticalApps\Northwind.Web\Pages\Suppliers.cshtml 34
Warning (active) CS8602	Dereference of a possibly null reference. Northwind.Web C:\cs12dotnet8\PracticalApps\Northwind.Web\Pages\Suppliers.cshtml 38
Warning (active) CS8602	Dereference of a possibly null reference. Northwind.Web C:\cs12dotnet8\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 to avoid runtime errors and to remove the compiler error about this, 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();
}

Warning! If you just set the Supplier property to = null!; to remove the compiler error, then runtime errors could still occur whenever the property actually is null.

Page 694 - Exercise 13.3 – Enabling HTTP/3 and request decompression support

Thanks to Phil Edmunds for raising this issue on January 20, 2024 and to RTD for discovering why Kestrel adds the HTTP/3 header but Chrome does not show it using HTTP/3 and a link to a work around on March 10, 2024.

This exercise is about enabling HTTP/3 and testing it. The following online page has step-by-step instructions with a localhost-hosted website: https://github.com/markjprice/cs12dotnet8/blob/main/docs/ch13-enabling-http3.md

Unfortunately, "Browsers don't allow self-signed certificates on HTTP/3, such as the Kestrel development certificate", as described here: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/servers/kestrel/http3#localhost-testing

The official documentation does not show a work around because Microsoft decided the steps are too difficult. You can read about the issue here if you want to try the complex workaround: dotnet/AspNetCore.Docs#23700. RTD wrote more detailed instructions that you can read here: #15 (comment).

In the next edition, I will add a note about this and remove the step-by-step instructions to try to test it.

Page 714 - Route constraints

At the top of the page, I wrote, "Use colons to separate multiple constraints, as shown in the following example:"

[Route("employees/{years:int:minlength(3)}")]
public Employees[] GetLoyalEmployees(int years)

But minlength is for checking the minimum length of a string, not the size of an int. The example should be as shown in the following code:

[Route("employees/{years:int:min(3)}")]
public Employees[] GetLoyalEmployees(int years)

Page 753 - Reviewing Blazor routing, layouts, and navigation

In Step 6, I wrote that there are three menu items. There are only two. And in the markup, the icon class names should end with -nav-menu, for example, bi-house-door-fill-nav-menu not bi-house-door-fill.

Page 761 - Using Bootstrap icons

In Step 1, I showed the CSS for the Bootstrap icons, but the icon class names should end with -nav-menu, as shown in the following markup:

.bi-house-door-fill-nav-menu {
    background-image: url("data:image/svg+xml,...");
}

.bi-plus-square-fill-nav-menu {
    background-image: url("data:image/svg+xml,...");
}

.bi-list-nested-nav-menu {
    background-image: url("data:image/svg+xml,...");
}

In Step 3, I wrote, "In the Search Bootstrap Icons box, enter globe, and note that six globe icons are found."

There are two input boxes on the web page, one labelled Search Icons and one labelled Filter Icons. You should enter globe in the Filter Icons box.

Page 771 - Building a customer detail component

Thanks to Paul Marangoni for raising this issue on June 28, 2024

In Step 2, the markup uses the Bootstrap 4 class named form-group. But the Blazor project template uses Bootstrap 5.1, as shown at the following link: https://github.com/markjprice/cs12dotnet8/blob/main/code/PracticalApps/Northwind.Blazor/wwwroot/bootstrap/bootstrap.min.css

In Bootstrap 5 and later, the form-group class has been removed and replaced with more simplified and flexible form controls. Instead of form-group, you can simply use the <div> element without any special class. Bootstrap 5 focuses on utility classes for spacing and layout. Labels and inputs should use the form-label and form-control classes respectively. For horizontal forms, Bootstrap 5.3 has new classes like row and col for layout. Use spacing utilities like mb-3 for margin-bottom to add spacing between form elements.

In the next edition, I will update the markup, as shown in the following code:

<EditForm Model="@Customer" OnValidSubmit="@OnValidSubmit">
  <DataAnnotationsValidator />
  <div>
    <label class="form-label">Customer Id</label>
    <div>
      <InputText class="form-control" @bind-Value="@Customer.CustomerId" />
      <ValidationMessage For="@(() => Customer.CustomerId)" />
    </div>
  </div>
  <div>
    <label class="form-label">Company Name</label>
    <div>
      <InputText class="form-control" @bind-Value="@Customer.CompanyName" />
      <ValidationMessage For="@(() => Customer.CompanyName)" />
    </div>
  </div>
  <div>
    <label class="form-label">Address</label>
    <div>
      <InputText class="form-control" @bind-Value="@Customer.Address" />
      <ValidationMessage For="@(() => Customer.Address)" />
    </div>
  </div>
  <div>
    <label class="form-label">Country</label>
    <div>
      <InputText class="form-control" @bind-Value="@Customer.Country" />
      <ValidationMessage For="@(() => Customer.Country)" />
    </div>
  </div>
  <button class="form-control" type="submit" class="btn btn-@ButtonStyle">@ButtonText</button>
</EditForm>

Appendix - Page 1 - Exercise 1.1 – Test your knowledge

Thanks to Ikarmus in the book's Discord channel for raising this issue.

In question 1, I wrote "Interactive Development Environment (IDE)". This should be "Integrated Development Environment (IDE)".