cs11dotnet7/docs/errata/errata.md

Errata (34 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
• Page 11 - Understanding the journey to one .NET and Understanding .NET support
• Page 36 - Getting help for the dotnet tool
• Page 37 - Getting definitions of types and their members
• Page 83 - Formatting using numbered positional arguments
• Page 83 - Formatting using interpolated strings
• Page 85 - Getting text input from the user
• Page 86 - Getting text input from the user
• Page 114 - Simplifying switch statements with switch expressions
• Page 156 - Calculating factorials with recursion
• Page 166 - Setting a breakpoint and starting debugging - Using Visual Studio 2022
• Page 178 - Reviewing project packages
• Page 180 - Reviewing project packages
• Page 185 - Creating a class library that needs testing
• Page 188 - Running unit tests using Visual Studio Code
• Page 231 - Requiring properties to be set during instantiation
• Page 244 - Init-only properties
• Page 258 - Defining and handling events
• Page 272 - Defining struct types
• Page 275 - Releasing unmanaged resources
• Page 277 - Making a value type nullable
• Page 279 - Declaring non-nullable variables and parameters
• Page 322 - Revealing the location of a type
• Page 330 - Publishing a self-contained app, Page 354 - Exercise 7.3 – Explore PowerShell
• Page 399 - Managing directories
• Page 362 - Joining, formatting, and other string members
• Page 412 - Compressing streams
• Page 477 - Inserting entities
• Page 548 - Creating a class library for a Northwind database context
• Page 551 - Creating a class library for entity models using SQL Server
• Page 627 - Defining a typed view
• Page 631 - Passing parameters using a route value
• Page 641 - Enabling role management and creating a role programmatically
• Page 649 - Varying cached data by query string
• Page 707 - Reviewing the Blazor Server project template
• Page 724 - Getting entities into a component
• Page 733 - Building customer create, edit, and delete components

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 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 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.

Figure 1.1: Go To Definition file tab generated from metadata

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.

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

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}.");

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 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, and a special thanks to Huynh Loc Le, who identified that the issue was caused by a Microsoft bug.

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 version 7.0.3, it has a bug that causes an exception to 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()

Until Microsoft fixes the bug, use version 7.0.2, the latest version that works correctly, as shown in the following markup:

<ItemGroup>
  <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="7.0.2" />
  <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="7.0.0" />

  <!--The following packages are included anyway due to dependencies-->
  <!--<PackageReference Include="Microsoft.Extensions.Configuration.FileExtensions" Version="7.0.0" />-->
  <!--<PackageReference Include="Microsoft.Extensions.Configuration" Version="7.0.0" />-->
</ItemGroup>

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 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 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 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 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 362 - Joining, formatting, and other string members

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

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 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 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 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;
  }
}

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 548 - Creating a class library for a Northwind database context
• Page 551 - Creating a class library for entity models using SQL Server

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");
}