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cs11dotnet7/docs/errata/errata.md
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Errata (47 items)

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

Microsoft has changed their domain for documentation from https://docs.microsoft.com to https://learn.microsoft.com with an automatic redirect so all links in my books that use the docs domain should still work.

Page 4, 8 - Pros and cons of the .NET Interactive Notebooks extension, 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. The engine is still named .NET Interactive.

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 8 - Installing other extensions

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. If you want to use them, then I have written instructions in the improvements page and I will use these in the next edition.

More Information: You can read the announcement about C# Dev Kit at the following link: https://devblogs.microsoft.com/visualstudio/announcing-csharp-dev-kit-for-visual-studio-code/

Page 11 - Understanding the journey to one .NET and Understanding .NET support

Even-numbered .NET releases like .NET 6 and .NET 8 have a support level named Long Term Support (LTS) with a duration of 3 years. Odd-numbered .NET releases like .NET 5 and .NET 7 had a support level named Current with a duration of 18 months.

On June 6, 2022, the .NET team proposed to change the support level name from Current to Short Term Support (STS) to complement the existing Long Term Support (LTS). I updated the drafts of my book to reflect that change.

On October 11, 2022, the .NET team changed the name again, to Standard Support, probably because Microsoft Marketing decided that "short term" sounded too negative. My editors and I scrambled to update the final drafts of my book to reflect that change.

On October 28, 2022, the .NET team changed the name again, to Standard Term Support (STS), probably because an initialism of SS is problematic and internal code and configuration was already using sts. Sadly, it was too late to update the PDFs that are sent to print.

Sigh. Such are the perils of trying to be up-to-date on release day.

Page 28 - Writing code using Visual Studio Code

In Step 18, 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.

Page 31 - Adding a second project using Visual Studio Code

In Step 7, 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.

Page 36 - Getting help for the dotnet tool

Step 1 is about opening a web browser to show the documentation for a dotnet command. It follows this syntax:

dotnet help <command>

I gave the example of dotnet help new, and although this worked in .NET Core 3.1 to .NET 6, with .NET 7 it gives an unhelpful error!

Other examples, like dotnet help run, work correctly by opening a web browser to show the run command's documentation.

The other type of help, as described in Step 2, is command-line documentation. It follows this syntax:

dotnet <command> -?|-h|--help

For example, dotnet new -? or dotnet new -h or dotnet new --help outputs documentation about the new command at the command-line.

Interestingly, dotnet help help opens a web browser for the help command, and dotnet help -h outputs documentation for the help command at the command-line!

Page 37 - Getting definitions of types and their members

In Step 3, I wrote, "Click inside int and then right-click and choose Go To Definition."

Visual Studio 2022 used to show code reverse-engineered from metadata for the selected type like int (see Figure 1.1), including the comments that I talk about in the book, but it now shows Source Link code (see Figure 1.2) which does not have comments.

from metadata code

Figure 1.1: Go To Definition file tab generated from metadata

SourceLink code

Figure 1.2: Go To Definition file tab retrieved from embedded Source Link code

To change back to the original Visual Studio 2022 behavior that is described in the book, please follow these steps:

  1. In Visual Studio 2022, navigate to Tools | Options.
  2. In the Options dialog, navigate to Text Editor | C# | Advanced.
  3. In the Go To Definition section, clear the check box named Enable navigation to Source Link and Embedded sources, as shown in Figure 1.3.
  4. Click OK.

Disabling Source Link for the Go To Definition feature

Figure 1.3: Disabling Source Link for the Go To Definition feature

Page 75 - Comparing double and decimal types

Thanks to Papa Smurf for raising this issue on 31 March 2023.

At the end of the last paragraph, I mention a method that can determine if a number value is not-a-number. The method name was written in the book as IsNan. It should be IsNaN.

Page 83 - Formatting using numbered positional arguments

At the end of the section, I say, "The Write, WriteLine, and Format methods can have up to four numbered arguments, named arg0, arg1, arg2, and arg3."

But the methods can only have up to three named arguments. I should have said, "The Write, WriteLine, and Format methods can have up to three numbered arguments, named arg0, arg1, and arg2. If you need to pass more than three values, then you cannot name the arguments using arg0 and so on, as shown in the following code:"

// Passing three values can use named arguments.
Console.WriteLine(
 format: "{0} {1} lived in {2}.", 
 arg0: "Roger", arg1: "Cevung", arg2: "Stockholm");

// Passing four or more values cannot use named arguments.
Console.WriteLine(
 "{0} {1} lived in {2} and worked in the {3} team at {4}.", 
 "Roger", "Cevung", "Stockholm", "Education", "Optimizely");

Page 83 - Formatting using interpolated strings

In Step 1, you enter some statements to output some variables using an interpolated string, as shown in the following code:

// The following statement must be all on one line.
Console.WriteLine($"{numberOfApples} apples cost {pricePerApple * numberOfApples:C}");

The comment says that it "must be all on one line". This is true for C# 10 and earlier (which is the default compiler if you target .NET 6), but if you use C# 11 then an expression inside an interpolation hole like {pricePerApple * numberOfApples:C} can now include line breaks. So we can, for example, enter the statement like this:

// The following statement must be all on one line when using C# 10 or earlier.
// If using C# 11, we can include a line break, as shown here:
Console.WriteLine($"{numberOfApples} apples cost {pricePerApple 
  * numberOfApples:C}");

Page 85 - 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 86 - Getting text input from the user

In Step 3, I wrote, "For the firstName variable" when I should have written, "For the age variable".

Page 114 - Simplifying switch statements with switch expressions

Thanks to Ricky for raising this issue on 25 January 2023.

In Step 1, the code statement that outputs the four-legged cat information is missing the word "named", as shown in the following code:

Cat fourLeggedCat when fourLeggedCat.Legs == 4
  => $"The cat {fourLeggedCat.Name} has four legs.",

It should be:

Cat fourLeggedCat when fourLeggedCat.Legs == 4
  => $"The cat named {fourLeggedCat.Name} has four legs.",

Page 116 - Looping with the do statement

Thanks to Norbert Duenki who raised this issue by email on 4 April 2023.

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 156 - Calculating factorials with recursion

Thanks to Ricky for raising this issue on 29 January 2023.

In Step 1, in the third bullet that explains the code, I wrote, "If the input parameter number is more than 1, which it will be in all other cases..." I should have written, "If the input parameter number is more than 0, which it will be in all other cases..."

Page 166 - Setting a breakpoint and starting debugging - Using Visual Studio 2022

Thanks to Masoud Nazari for raising this issue on 12 February 2023.

At the end of this section I wrote, "If you do not want to see how to use Visual Studio Code to start debugging, then you can skip the next section and continue to the section titled Navigating with the debugging toolbar."

But the immediately following section is Navigating with the debugging toolbar. The paragraph should move to after this section and before the section titled Using Visual Studio Code, and it should say, "If you do not want to see how to use Visual Studio Code to start debugging, then you can skip the next section and continue to the section titled Debugging windows."

Page 178 - Reviewing project packages

Thanks to Nick Bettes and Zhang Cheng for raising this issue on 16 February 2023, a special thanks to Huynh Loc Le, who identified that the issue was caused by a Microsoft fix to one of their bugs, and finally thanks to richshi who raised this issue again on 28 June 2023 and consequently made me dig deeper to find a more complete explanation and solution.

In Step 1, you add package references to enable an appsettings.json file to configure a trace switch. If you reference Microsoft.Extensions.Configuration.Binder package versions 7.0.3 or later, then they have fixed a bug, but the fix causes a regression in expected behavior which means that unless we change how we set the trace switch level an exception will be thrown, as shown in the following output:

Reading from appsettings.json in C:\cs11dotnet7\Chapter04\Instrumenting\bin\Debug\net7.0
Unhandled exception. System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> System.ArgumentException: Must specify valid information for parsing in the string. (Parameter 'value')
   at System.Enum.TryParse[TEnum](ReadOnlySpan`1 value, Boolean ignoreCase, Boolean throwOnFailure, TEnum& result)
   at System.Enum.TryParse[TEnum](String value, Boolean ignoreCase, Boolean throwOnFailure, TEnum& result)
   at System.Enum.Parse[TEnum](String value, Boolean ignoreCase)
   at System.Diagnostics.TraceSwitch.OnValueChanged()

Originally, it seemed the best solution was to avoid the later versions that cause the changed behavior, so I advised to use 7.0.2 or earlier. But the change in 7.0.3 was to fix a bug, so we really need a solution that will allow us to use the latest package version and also works for older versions too.

To fix the issue, we can set both the Level property and the Value property of the trace switch, as shown in the following code:

{
  "PacktSwitch": {
    "Value": "Info", // Must be set to work with 7.0.3 or later.
    "Level": "Info" // Works with 7.0.2 or earlier including .NET 6.
  }
}

In the eighth edition, I will instruct readers to just set the Value property because this implicitly sets the Level as well.

See the following explanation from Microsoft about the bug they fixed that cause this problem: https://github.com/dotnet/runtime/issues/82998

See also this common mistake item: https://github.com/markjprice/cs11dotnet7/blob/main/docs/errata/common-errors.md#microsoft-introduces-a-bug-in-a-later-version

Page 180 - Reviewing project packages

Thanks to TheKuroEver for raising this issue on 7 March 2023.

In Step 6, I tell you to write a statement to add the appsettings.json file to the configuration builder so that it can be used to set the trace switch level. But in the print book, it sets the optional parameter to true when it should be false.

Fix the issue by setting the optional parameter to false, as shown in the following code:

builder.AddJsonFile("appsettings.json", 
  optional: false, reloadOnChange: true);

The statement was already correct in GitHub: https://github.com/markjprice/cs11dotnet7/blob/main/vs4win/Chapter04/Instrumenting/Program.cs#L28

The optional parameter controls if the statement throws an exception at runtime if the file is missing. We want to ensure that we are notified with an exception if the file is missing, for example, as shown in the following output:

Reading from appsettings.json in C:\cs11dotnet7\Chapter04\Instrumenting\bin\Debug\net7.0
Unhandled exception. System.IO.FileNotFoundException: The configuration file 'appsettings.json' was not found and is not optional. The expected physical path was 'C:\cs11dotnet7\Chapter04\Instrumenting\bin\Debug\net7.0\appsettings.json'.
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.HandleException(ExceptionDispatchInfo info)
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.Load(Boolean reload)
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.Load()
   at Microsoft.Extensions.Configuration.ConfigurationRoot..ctor(IList`1 providers)
   at Microsoft.Extensions.Configuration.ConfigurationBuilder.Build()
   at Program.<Main>$(String[] args) in C:\cs11dotnet7\Chapter04\Instrumenting\Program.cs:line 30

If we set the optional parameter to true and the appsettings.json file is missing then this exception will not be thrown BUT the trace switch will not be set by the file and therefore defaults to Off. Therefore no output is written to the log.txt file on the desktop for the trace switch.

In the next edition, I will add a statement after binding to the packt switch configuration that outputs the trace switch level to the Console to make it clearer when there might be a problem because either the trace switch is set to Off or the appsettings.json file is missing and it has been made optional, as shown in the following code:

configuration.GetSection("PacktSwitch").Bind(ts);

// Output the trace switch level.
Console.WriteLine($"Trace switch level: {ts.Level}");

Page 185 - Creating a class library that needs testing

In the "If you are using Visual Studio Code" section, in Step 5, the command in the book is dotnet new console but it should have been dotnet new classlib.

Page 188 - 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 231 - Requiring properties to be set during instantiation

Thanks to Masoud Nazari for raising this issue on 1 March 2023.

In Step 1, you are told to add a new class library project named PacktLibraryModern.

In Step 4, in the PeopleApp console app project, you are told to create an instance of the Book class that is defined in the class library. To do so, you must have added a reference to the PacktLibraryModern project.

In the next edition, I will add steps before Step 4 to remind readers how to do this, as shown below:

If you are using Visual Studio 2022:

  • In Solution Explorer, select the PeopleApp project, navigate to Project | Add Project Reference…, check the box to select the PacktLibraryModern project, and then click OK.

If you are using Visual Studio Code:

  • Edit PeopleApp.csproj to add a project reference to PacktLibraryModern, as shown in the following markup:
<ItemGroup>
  <ProjectReference Include="../PacktLibraryModern/PacktLibraryModern.csproj" />
</ItemGroup>
  • Build the PeopleApp project.

Page 235 - More about methods

Thanks to cgwid for raising this issue on 12 April 2023.

In this section, we define some methods and operators so that two Person objects can get married and have babies. The example we model comes from the Bible story of Lamech and his two wives and their children. But the code I tell you to write does not allow Lamech to marry two women so later an exception is thrown when Lamech and his second wife try to make a baby.

cgwid suggested a solution in the issue they raised. I want to rethink this code example for the next edition to avoid it becoming overly complex so I will leave it to the reader to decide how they might want to solve it. Meanwhile, I have added an improvement with suggested alternative code here: https://github.com/markjprice/cs11dotnet7/blob/main/docs/errata/improvements.md#page-235---more-about-methods

Page 244 - Init-only properties

Thanks to Bob Molloy for raising this issue via email.

In Step 1, I say to add a new file named Records.cs to the PacktLibraryNetStandard2 project/folder. I should have said to the PacktLibraryModern project/folder.

Page 256 - Defining and handling delegates

Thanks to bfdhud for raising this issue via Discord.

In Step 2, if you use Visual Studio 2022 to create the class file then it will have multiple statements of existing code. These statements should be deletd and replaced with the code as shown in Step 3. If you just add new statements inside those created by Visual Studio 2022 then it won't work because the partial Program class needs to be in the default empty namespace just like the auto-generated Program class is.

A similar issue is covered by these improvement items: https://github.com/markjprice/cs11dotnet7/blob/main/docs/errata/improvements.md#page-149---writing-a-times-table-function https://github.com/markjprice/cs11dotnet7/blob/main/docs/errata/improvements.md#page-241---defining-flight-passengers

In the next edition I will add notes to warn Visual Studio 2022 users to delete any existing statements.

Page 258 - Defining and handling events

Thanks to Ricky for raising this issue on 2 February 2023.

In Step 5, the statement that outputs the "Stop it!" message uses the $ string interpolation prefix character unnecessarily, as shown in the following code:

WriteLine($"Stop it!");

The $ can be removed, as shown in the following code:

WriteLine("Stop it!");

Page 263 - Comparing objects using a separate class

Thanks to Masoud Nazari for raising this issue on 15 March 2023.

In Step 1, the following comment has an extra slash:

/// ...if they are equal...

It should be:

// ...if they are equal...

Page 272 - Defining struct types

Thanks to Ali Koleiny Zadeh for raising this issue on 15 January 2023.

In Step 4, the output should be formatted using the "command line" style like in Step 6 instead of the "code" style so that it has the black background.

Page 275 - Releasing unmanaged resources

Thanks to Wuu#0348 on the Packt Discord channels 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 ~ObjectWithUnmanagedResources 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 ~ObjectWithUnmanagedResources method, then unmanaged resources will already have been deallocated and only managed resources remain to be deallocated by the garbage collector." I will do this in the next edition.

Page 277 - Making a value type nullable

Thanks to Ricky for raising this issue on 2 February 2023.

In Step 6, the output should be formatted with a black background like other command-line blocks, and the output is missing the writing of the variable named thisCannotBeNull. The output should be:

4

0
7
7

Step 7 should therefore say, "The second line is blank because it is outputting the null value!", and it should not be formatted as a numbered step because it is a not an instruction to the reader, it is a note.

Page 279 - Declaring non-nullable variables and parameters

Thanks to Ricky for raising this issue on 19 February 2023.

In Step 1, I wrote, "In NullHandling.csproj," which could be confusing because you do not need to modify that file. I should have written, "In the NullHandling project," because you need to add a new file to the project.

Page 322 - Revealing the location of a type

Thanks to Bob Molloy for raising this issue via email.

In Steps 2 and 5, I say to "Navigate to the top of the code file and note the assembly filename..."

If you have Source Link enabled, then you will not see the filename. I recommend that you disable Source Link.

If you have Source Link disabled, then to see the filename you must expand the collapsed region. You will then find the assembly filename within the region, as shown in the following code:

#region Assembly System.Runtime, Version=7.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
// C:\Program Files\dotnet\packs\Microsoft.NETCore.App.Ref\7.0.0\ref\net7.0\System.Runtime.dll
#endregion

Page 330 - Publishing a self-contained app, Page 354 - Exercise 7.3 – Explore PowerShell

In the Good Practice box on page 330, 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 next 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 357 - Working with complex numbers

Thanks to Masoud Nazari for raising this issue on 25 March 2023.

In Step 2, I show the default formatting for complex numbers i.e. using round brackets and commas, as well as a custom format, as shown in the following output:

(4, 2) added to (3, 7) is (7, 9)
4 + 2i added to 3 + 7i is 7 + 9i

See the official documentation for the Complex.ToString method here: https://learn.microsoft.com/en-us/dotnet/api/system.numerics.complex.tostring

Although this is the behavior in .NET 6, in .NET 7 (and .NET 8 previews), the formatting of complex numbers uses angle brackets and semi-colons, as shown in the following output:

<4; 2> added to <3; 7> is <7; 9>
4 + 2i added to 3 + 7i is 7 + 9i

In the next edition, I will add a note about this. Since the official documentation still shows the behavior of .NET 6, this seems odd. My guess is that they decided to change to angle brackets and semi-colons because some cultures use round brackets to indicate negative numbers and use commas for decimal numbers. Therefore it would be confusing to have a mix of round brackets and commas meaning different things. Its a shame the documentation does not explain this and show the .NET 7 and later new default formats.

Page 362 - Joining, formatting, and other string members

In the table, string.IsNullOrWhitespace should be string.IsNullOrWhiteSpace.

Page 399 - Managing directories

Thanks to Dario Bosco for raising this issue on 6 February 2023.

In Step 1, in the second bullet, I wrote, "Check for the existence of the custom directory path using the Exists method of the Directory class." But in the code I used the Exists method of the Path class. We have statically imported both the Path and the Directory classes and they both have an Exists method in .NET 7. If we try to call an Exists method without a classname prefix we get a compile error due to ambiguity of which one to call. After writing the second bullet text, I changed the code from using Directory to using Path simply because it is shorter. In the 8th edition, I will add a note about this since it is useful for the reader to understand my choice and how the reader could have done it differently.

Note: the Path.Exists method was added in .NET 7. It is not available in earlier versions of .NET.

Page 412 - Compressing streams

Thanks to Bob Molloy for raising this issue via email.

In Step 2, the following statement enables interpolated strings unnecessarily:

WriteLine($"The compressed contents:");

It should be:

WriteLine("The compressed contents:");

Page 454 - Scaffolding models using an existing database

Thanks to Masoud for raising this issue on 6 April 2023.

Category class changes

In Step 5, I show the class that represents a Category in the Northwind database that is generated by the dotnet-ef, as shown in the following code:

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.EntityFrameworkCore;

namespace WorkingWithEFCore.AutoGen
{
  [Index("CategoryName", Name = "CategoryName")]
  public partial class Category
  {
    public Category()
    {
      Products = new HashSet<Product>();
    }

    [Key]
    public int CategoryId { get; set; }

    [StringLength(15)]
    public string CategoryName { get; set; }

    [Column(TypeName = "ntext")]
    public string? Description { get; set; }

    [Column(TypeName = "image")]
    public byte[]? Picture { get; set; }

    [InverseProperty("Category")]
    public virtual ICollection<Product> Products { get; set; }
  }
}

The current dotnet-ef tool generates slightly different output, for example, it uses a file-scoped namespace declaration to avoid indenting and it initializes the Products property to a List<T> instead of a HashSet<T>, as shown in the following code:

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using Microsoft.EntityFrameworkCore;

namespace WorkingWithEFCore.AutoGen;

[Index("CategoryName", Name = "CategoryName")]
public partial class Category
{
  [Key]
  public int CategoryId { get; set; }

  [StringLength(15)]
  public string CategoryName { get; set; } = null!;

  [Column(TypeName = "ntext")]
  public string? Description { get; set; }

  [Column(TypeName = "image")]
  public byte[]? Picture { get; set; }

  [InverseProperty("Category")]
  public virtual ICollection<Product> Products { get; } = new List<Product>();
}

NorthwindDb class changes

In Step 7, I show the class that represents the Northwind database that was generated by the dotnet-ef tool. The current dotnet-ef tool generates slightly different output, for example, it uses a file-scoped namespace declaration to avoid indenting and it does not set each DbSet<T> property to the null-forgiving operator, as shown in the following code:

// older version of dotnet-ef did this:
public virtual DbSet<Category> Categories { get; set; } = null!;

// current version of dotnet-ef does this:
public virtual DbSet<Category> Categories { get; set; }

Page 477 - Inserting entities

Thanks to Chadwick Geyser for raising this issue on 29 November 2022.

In Step 4, the code statement to list the products uses an older version of the method signature that I removed before publishing that only allows a single productId to be highlighted, as shown in the following code:

ListProducts(productIdToHighlight: resultAdd.productId);

It should use the method signature that allows multiple productIds to be highlighted, as shown in the following code:

ListProducts(productIdsToHighlight: new[] { resultAdd.productId });

Page 478 - Updating entities

Thanks to Masoud for raising this issue on 11 April 2023.

In Step 2, the statement to output the price increase, as shown in the following code:

WriteLine("Increase price success for ID: {resultUpdate.productId}.");

Is missing the $ prefix to make it an interpolated string, as shown in the following code:

WriteLine($"Increase price success for ID: {resultUpdate.productId}.");

Page 495 - Filtering entities with Where

Thanks to Masoud for raising this issue on 20 April 2023.

In Steps 3 and 5, the screenshots in Figure 11.1 and Figure 11.2 show a solution name of Chapter12 when it should be Chapter11. In the next edition, I will retake the screenshots.

Page 548 - 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 550 - Creating a class library for entity models using SQL Server

Thanks to Amer Cejudo for raising this issue by email on 8 April 2023.

In Step 6, I tell the reader to enter a command to generate code from an existing SQL Server database, as shown in the following command:

dotnet ef dbcontext scaffold "Data Source=.;Initial Catalog=Northwind;Integrated Security=true;" Microsoft.EntityFrameworkCore.SqlServer --namespace Packt.Shared --data-annotations

If you get the error, "The certificate chain was issued by an authority that is not trusted.", then it is because the connection to the SQL Server database will be encrypted by default but the OS and therefore the app does not (yet) trust the local development server certificate.

You have three choices to fix this issue:

  1. Add the following to the database connection string to make the certicate trusted for this connection:
TrustServerCertificate=true;
  1. Add the following to the database connection string to disable encryption so it does not need to trust the certificate for this connection:
Encrypt=false;
  1. Run the following at the command-line to trust the certificate for all .NET apps in future:
dotnet dev-certs https --trust

Page 551 - Creating a class library for entity models using SQL Server

In Step 15, 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 627 - Defining a typed view

Thanks to Chadwick Geyser for raising this issue on 4 December 2022.

In Step 3, the code in the book to render the carousel indicators has an incorrect attribute named data-slide-to, as shown in the following markup:

<li data-bs-target="#categories" data-slide-to="@c" 
    class="@currentItem"></li>

Should be data-bs-slide-to, as shown in the following markup:

<li data-bs-target="#categories" data-bs-slide-to="@c" 
    class="@currentItem"></li>

It was already correct in the GitHub copy of the code.

Page 631 - Passing parameters using a route value

Thanks to Bob Molloy for raising this issue via email.

In Step 3, the statements attempt to output the values of the category name and unit price for the product, as shown in the following markup:

<dt>Category</dt>
<dd>@Model.CategoryId - @Model.Category.CategoryName</dd>
<dt>Unit Price</dt>
<dd>@Model.UnitPrice.Value.ToString("C")</dd>

But since the Category and UnitPrice properties could be null, we should use a null checks, as shown in the following markup:

<dt>Category</dt>
<dd>@Model.CategoryId - @Model.Category?.CategoryName</dd>
<dt>Unit Price</dt>
<dd>@(Model.UnitPrice is null ? "zero" : Model.UnitPrice.Value.ToString("C"))</dd>

Page 641 - Enabling role management and creating a role programmatically

Thanks to Bob Molloy for raising this issue via email.

In Step 2, in the Index action method, the variable declaration for finding the email of the user is not nullable, as shown in the following code:

IdentityUser user = await userManager.FindByEmailAsync(UserEmail);

It should be nullable, as shown in the following code:

IdentityUser? user = await userManager.FindByEmailAsync(UserEmail);

It was already correct in the GitHub copy of the code.

Page 649 - Varying cached data by query string

Thanks to Chadwick Geyser for raising this issue on 5 December 2022.

In Step 1, when defining a policy for output caching, the statement uses the method VaryByQuery, as shown in the following code:

options.AddPolicy("views", p => p.VaryByQuery(""));

The method name changed in Release Candidate 2, as described here, so statement should be changed to use the new method SetVaryByQuery, as shown in the following code:

options.AddPolicy("views", p => p.SetVaryByQuery(""));

Page 707 - Reviewing the Blazor Server project template

Thanks to Bob Molloy for raising this issue on 19 December 2022.

In Steps 6 and 7, I wrote that there are two files that combine to product the home page for a Blazor Server project, named _Host.cshtml and _Layout.cshtml.

Microsoft changed this project template to merge them together so there is no shared layout file named _Layout.cshtml. The markup is now all in the _Host.cshtml file, as shown in the following markup:

@page "/"
@using Microsoft.AspNetCore.Components.Web
@namespace Northwind.BlazorServer.Pages
@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <base href="~/" />
    <link rel="stylesheet" href="css/bootstrap/bootstrap.min.css" />
    <link href="css/site.css" rel="stylesheet" />
    <link href="Northwind.BlazorServer.styles.css" rel="stylesheet" />
    <link rel="icon" type="image/png" href="favicon.png"/>
    <component type="typeof(HeadOutlet)" render-mode="ServerPrerendered" />
</head>
<body>
    <component type="typeof(App)" render-mode="ServerPrerendered" />

    <div id="blazor-error-ui">
        <environment include="Staging,Production">
            An error has occurred. This application may no longer respond until reloaded.
        </environment>
        <environment include="Development">
            An unhandled exception has occurred. See browser dev tools for details.
        </environment>
        <a href="" class="reload">Reload</a>
        <a class="dismiss">🗙</a>
    </div>

    <script src="_framework/blazor.server.js"></script>
</body>
</html>

Page 724 - Getting entities into a component

Thanks to Amer Cejudo (via email) and Christopher Targett-Adams for raising this issue on 20 February 2023.

In Step 4, I tell the reader to write a statement to call an extension method that you previously created in Chapter 12, as shown in the following code:

builder.Services.AddNorthwindContext();

By default, this statement registers the database context with Scope lifetime. This is not a problem with most ASP.NET Core projects. But in a Blazor Server project the Scope lifetime database context instance is shared between multiple threads running on the server. This can cause concurrency issues as described here: https://learn.microsoft.com/en-us/ef/core/dbcontext-configuration/#implicitly-sharing-dbcontext-instances-via-dependency-injection

This often only affects the SQL Server database provider but it is best to apply the code change for both SQL Server and SQLite class libraries. To fix this issue, please make the changes as shown in the following items:

Page 733 - Building customer create, edit, and delete components

Thanks to Bob Molloy for raising this issue on 27 December 2022.

In Step 4, in the file named EditCustomer.razor, the code for the Update method is missing the last statement to navigate to the customers page component after updating the customer in the database, as shown in the following code:

private async Task Update()
{
  if (customer is not null)
  {
    await service.UpdateCustomerAsync(customer);
  }

  navigation.NavigateTo("customers");
}