If you find any mistakes, then please [raise an issue in this repository](https://github.com/markjprice/cs11dotnet7/issues) 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-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-11---understanding-the-journey-to-one-net-and-understanding-net-support)
- [Page 166 - Setting a breakpoint and starting debugging - Using Visual Studio 2022](#page-166---setting-a-breakpoint-and-starting-debugging---using-visual-studio-2022)
- [Page 641 - Enabling role management and creating a role programmatically](#page-641---enabling-role-management-and-creating-a-role-programmatically)
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*.
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.
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)**](https://github.com/dotnet/announcements/issues/223) 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**](https://devblogs.microsoft.com/dotnet/announcing-dotnet-7-rc-2/#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)**](https://twitter.com/mairacw/status/1585789100879069185), 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.
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!
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.
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:"
In Step 1, you enter some statements to output some variables using an interpolated string, as shown in the following code:
```cs
// The following statement must be all on one line.
Console.WriteLine($"{numberOfApples} apples cost {pricePerApple * numberOfApples:C}");
```
The comment says that it "must be all on one line". This is true for C# 10 and earlier (which is the default compiler if you target .NET 6), but if you use C# 11 then an expression inside an interpolation hole like `{pricePerApple * numberOfApples:C}` can now include line breaks. So we can, for example, enter the statement like this:
```cs
// The following statement must be all on one line when using C# 10 or earlier.
// If using C# 11, we can include a line break, as shown here:
Console.WriteLine($"{numberOfApples} apples cost {pricePerApple
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.
```cs
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 156 - Calculating factorials with recursion
> Thanks to [Ricky](https://github.com/r1c5) for raising this [issue on 29 January 2023](https://github.com/markjprice/cs11dotnet7/issues/21).
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](https://github.com/MAS-OUD) for raising this [issue on 12 February 2023](https://github.com/markjprice/cs11dotnet7/issues/28).
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*."
> Thanks to [Nick Bettes](https://github.com/bettesn) and [Zhang Cheng](https://github.com/Matrix-Zhang) for raising this issue on [16 February 2023](https://github.com/markjprice/cs11dotnet7/issues/29), and a special thanks to [Huynh Loc Le](https://github.com/huynhloc-1110), 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:
> Thanks to [TheKuroEver](https://github.com/TheKuroEver) for raising this [issue on 7 March 2023](https://github.com/markjprice/cs11dotnet7/issues/37).
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:
```cs
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:
# 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`.
> Thanks to [kwatsonkairosmgt](https://github.com/kwatsonkairosmgt) for raising this [issue on 27 October 2022](https://github.com/markjprice/cs10dotnet6/issues/106).
In Step 1, the project name `CalculatorLibUnitTest` should be `CalculatorLibUnitTests`.
# Page 231 - Requiring properties to be set during instantiation
> Thanks to [Masoud Nazari](https://github.com/MAS-OUD) for raising this [issue on 1 March 2023](https://github.com/markjprice/cs11dotnet7/issues/33).
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
> 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.
> Thanks to [Ricky](https://github.com/r1c5) for raising this [issue on 2 February 2023](https://github.com/markjprice/cs11dotnet7/issues/23).
In Step 5, the statement that outputs the "Stop it!" message uses the `$` string interpolation prefix character unnecessarily, as shown in the following code:
```cs
WriteLine($"Stop it!");
```
The `$` can be removed, as shown in the following code:
# Page 263 - Comparing objects using a separate class
> Thanks to [Masoud Nazari](https://github.com/MAS-OUD) for raising this [issue on 15 March 2023](https://github.com/markjprice/cs11dotnet7/issues/43).
In Step 1, the following comment has an extra slash:
> Thanks to [Ali Koleiny Zadeh](https://github.com/alikzalikz) for raising this [issue on 15 January 2023](https://github.com/markjprice/cs11dotnet7/issues/18).
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.
> 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.
> Thanks to [Ricky](https://github.com/r1c5) for raising this [issue on 2 February 2023](https://github.com/markjprice/cs11dotnet7/issues/24).
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](https://github.com/r1c5) for raising this [issue on 19 February 2023](https://github.com/markjprice/cs11dotnet7/issues/30).
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.
> 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](#page-37---getting-definitions-of-types-and-their-members).
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:
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.
> Thanks to [Dario Bosco](https://github.com/DarioBosco) for raising this [issue on 6 February 2023](https://github.com/markjprice/cs11dotnet7/issues/26).
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.
> Thanks to [Chadwick Geyser](https://github.com/chadwickgeyser) for raising this [issue on 29 November 2022](https://github.com/markjprice/cs11dotnet7/issues/5).
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:
# 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:
```cs
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>
/// <paramname="services"></param>
/// <paramname="relativePath">Set to override the default of ".."</param>
/// <paramname="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(
# 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:
```cs
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>
/// <paramname="services"></param>
/// <paramname="connectionString">Set to override the default.</param>
/// <returns>An IServiceCollection that can be used to add more services.</returns>
public static IServiceCollection AddNorthwindContext(
> Thanks to [Chadwick Geyser](https://github.com/chadwickgeyser) for raising this [issue on 4 December 2022](https://github.com/markjprice/cs11dotnet7/issues/6).
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:
```xml
<lidata-bs-target="#categories"data-slide-to="@c"
class="@currentItem"></li>
```
Should be `data-bs-slide-to`, as shown in the following markup:
> Thanks to [Chadwick Geyser](https://github.com/chadwickgeyser) for raising this [issue on 5 December 2022](https://github.com/markjprice/cs11dotnet7/issues/7).
In Step 1, when defining a policy for output caching, the statement uses the method `VaryByQuery`, as shown in the following code:
```cs
options.AddPolicy("views", p => p.VaryByQuery(""));
```
The method name changed in Release Candidate 2, as described [here](https://learn.microsoft.com/en-us/dotnet/core/compatibility/aspnet-core/7.0/output-caching-renames), so statement should be changed to use the new method `SetVaryByQuery`, as shown in the following code:
```cs
options.AddPolicy("views", p => p.SetVaryByQuery(""));
> Thanks to [Bob Molloy](https://github.com/BobMolloy) for raising this [issue on 19 December 2022](https://github.com/markjprice/cs11dotnet7/issues/12).
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:
> Thanks to Amer Cejudo (via email) and [Christopher Targett-Adams](https://github.com/targettadams) for raising this [issue on 20 February 2023](https://github.com/markjprice/cs11dotnet7/issues/31).
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:
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:
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](https://github.com/BobMolloy) for raising this [issue on 27 December 2022](https://github.com/markjprice/cs11dotnet7/issues/15).
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:
