If you have suggestions for improvements, then please [raise an issue in this repository](https://github.com/markjprice/cs11dotnet7/issues) or email me at markjprice (at) gmail.com.
- [Page 586 - Creating a Razor class library, Page 587 - Implementing a partial view to show a single employee](#page-586---creating-a-razor-class-library-page-587---implementing-a-partial-view-to-show-a-single-employee)
> Thanks to [Mahdi Jaberzadeh Ansari](https://github.com/mjza) who raised this issue on [6 March 2023](https://github.com/markjprice/cs11dotnet7/issues/36).
In the example JSON used to illustrate a raw interpolated string literal, the comma after `"calculation"` should be a colon. Since we never use the JSON, it doesn't actually matter, but it would definitely be better as valid JSON, as shown in the following code:
```cs
var person = new { FirstName = "Alice", Age = 56 };
In Step 1, I note that the `ReadLine` method is declared to return `string?`, meaning that it could return a `null` value instead of a `string` value (including an empty one). I also note that this is treated as a warning by the compiler.
In the next edition, I will add a note to explain that this method never actually returns `null` so there is no point in checking for that in functional code. A more useful check is `string.IsNullOrEmpty` so I will add more steps to show how to use that method and `string.IsNullOrWhiteSpace` to validate text input.
In this section, I wrote about rounding rules as taught in schools and compare them to rounding rules when using C# and .NET. In schools, children are introduced to rounding rules with positive numbers and so learn the term "rounding up" and "rounding down". I did not explicitly say that for negative numbers, those terms would be reversed which can be confusing, so those terms should be avoided. This is why the .NET API uses the enum values `AwayFromZero`, `ToZero`, `ToEven`, `ToPositiveInfinity` and `ToNegativeInfinity` for improved clarity. In the next edition I will add a note about this.
WriteLine($"This is the {number} times table with {size} rows:");
for (int row = 1; row <= size; row++)
{
WriteLine($"{row} x {number} = {row * number}");
}
WriteLine();
}
}
```
If you use Visual Studio 2022 to create the `Program.Functions.cs` file from the **Class** project item template, then it wraps the class definition in a namespace (and imports some unnecessary namespaces), for example:
```cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace WritingFunctions
{
internal class Program
{
}
}
```
The namespace used by the `Program` class generated for the `Program.cs` file does not have a namespace (literally uses the `null` value for the name of its namespace), so the two `Program` classes never merge together as two `partial` definitions of a single class.
You must delete the namespace declaration so that the `partial Program` class in the `Program.Functions.cs` file is in the same `null` namespace.
In the next edition I will add a note explaining this, and I will change the Step 4 text to read: "In `Program.Functions.cs`, replace any existing code with new statements to define a function named `TimesTable` in the `partial Program` class, ..."
You can output the namespace of the `Program` class by getting the `Program` type information and checking if its `Namespace` property is `null`, as shown in the following code:
At the end of this section there is a note box that explains that we could use the `C` format code to format the output as currency. If you are running on a computer in a culture that uses Euros then to show the Euro currency symbol you must enable UTF-8 encoding.
Add the following statement near the top of the code file before doing any writing to the console:
# Page 161 - Using lambdas in function implementations
> Thanks to [Masoud Nazari](https://github.com/MAS-OUD) for raising this [issue on 8 March 2023](https://github.com/markjprice/cs11dotnet7/issues/39).
In the next edition, I will expand on the definition of **Immutability** e.g. a data value that cannot change. I will also note that C# `record` types are not necessarily immutable.
In Step 4, I tell Visual Studio 2022 readers to select the `appsettings.json` file and change its **Copy to Output Directory** to **Copy if newer**. To confirm this is done correctly, in the next edition, I will then tell them to review the change that was made to the project file, as shown in the following markup:
In the next edition, I will add a summary table of the different categories of type and their capabilities, as well as several paragraphs of explanation. Parts of it might go at the start of Chapter 5 as an introduction but most of it is likely to go at the end of Chapter 6 as a review that brings together all the details from the two chapters.
For me, the terms *inherit* and *implement* are different, and in the early days of C# and .NET you could strictly apply them to classes and interfaces respectfully. *Inherit* implies some functionality that a sub class gets "for free" from its base aka super class. *Implement* implies some functionality that is NOT inherited but instead MUST be provided by the sub class. This is why **Chapter 6** is titled, **Implementing Interfaces and Inheriting Classes**.
Before C# 8, interfaces were always purely contracts i.e. there was no functionality that you could *inherit*. In those days, you could strictly use the term *implement* for an interface that represents a list of members that your type must implement, and *inherit* for classes with functionality that your type can inherit and potentially override.
With C# 8, interfaces can now include default implementations, making them more like abstract classes, and the term *inherit* for an interface that has default implementations does make sense. But I feel uncomfortable with this capability as do many other .NET developers because it messes up what used to be a clean language design.
Classes can also have `abstract` members, for example, methods or properties without any implementation, just like an interface could have. When a sub class inherits from this class, they MUST provide an implementation of those abstract members. And the base class must be decorated with the `abstract` keyword to prevent it being instantiated using `new` because it is missing some functionality.
In Step 4, I tell the reader to write some code that uses the `??` operator. But I do not explain how this operator works until later in the book, on page 282, as shown in the following text and code example:
"Sometimes, you want to either assign a variable to a result or use an alternative value, such as `3`, if the
variable is `null`. You do this using the **null-coalescing operator**, `??`, as shown in the following code:
```cs
// result will be 3 if authorName?.Length is null
int result = authorName?.Length ?? 3;
Console.WriteLine(result);
```
In the 8th edition, I will add a similar explanation of the operator `??` to the **Chapter 3, Operating on variables** section.
> Thanks to [Masoud Nazari](https://github.com/MAS-OUD) for raising this [issue on 8 March 2023](https://github.com/markjprice/cs11dotnet7/issues/38).
In Step 1, you are told to add a new file named `FlightPatterns.cs`. If you use Visual Studio 2022, then this file will contain a class named `FlightPatterns`.
In Step 2, you are given the complete code for that file that defines a file-scoped namespace named `Packt.Shared` with several classes like `Passenger` in it. If you define those classes inside the Visual Studio-generated `FlightPatterns` class then you will later have problems referencing the nested classes.
In the next edition, I will add a note for Visual Studio readers to explicitly tell them to delete the class named `FlightPatterns` as well as providing the complete code for the `FlightPatterns.cs` file.
# Page 251 - Setting up a class library and console application
In Step 8, I wrote, "Run the `PeopleApp` project".
In Chapter 1, I explain how to control which project starts when a Visual Studio 2022 solution contains multiple projects by setting the startup project. In Chapters 2 to 5, I remind the reader to set the startup project.
In the 8th edition, I will add the same reminder to Chapter 6 as well, for example:
8. Set the `PeopleApp` project as the startup/active project:
> Thanks to [Masoud Nazari](https://github.com/MAS-OUD) for raising this [issue on 17 March 2023](https://github.com/markjprice/cs11dotnet7/issues/44).
In Step 1, I tell the reader to write a statement to output the values of two integers and if they are equal, as shown in the following code:
It is not necessary to wrap the equality expression in parentheses like this: `(a == b)`. In more complex expressions it might be necessary to control the order of a calculation, and some developers prefer adding parentheses, but here it is not needed, and some code editors like Visual Studio 2022 will recommend that they are removed.
This section shows how to follow best practice and treat warnings as errors. But doing so means you must write extra code in common scenarios to fix all warnings that will now be treated as errors that prevent compilation during the build process.
So this section also shows how to disable some common warnings by adding extra code. The project is NOT designed to be run. The code in it is written only to illustrate some common warnings and how to disable them to allow a build.
For example, one warning is caused by the compiler thinking there could be a null dereference. To disable the warning, you therefore need to check for a `null` value *even though we know that can never actually happen* as explained in the note. That extra code check is pointless if you run the console app and expect it to work correctly.
In the next edition, I will add another note to explicitly tell the reader not to run the project. The project implementation is not written to actually function as a check if someone has entered their name because that's not the point of this section. I will also simplify the code.
Current code:
```cs
if (name == null)
{
Console.WriteLine("You did not enter a name.");
return;
}
```
Code in next edition:
```cs
if (name == null) return; // must check for null to remove the warning
> Thanks to [Masoud Nazari](https://github.com/MAS-OUD) for raising this [issue on 24 March 2023](https://github.com/markjprice/cs11dotnet7/issues/48).
In the next edition, I will add a note to remind readers about this. I will also add the explantion in the errata item above to Chapter 1 when the feature is first introduced.
In Step 3, you modify `SharedLibrary.csproj` to add some elements to control how the class library is turned into a NuGet package. If you rely on IntelliSense then it could mislead you to use deprecated tag names. For example, `<PackageIconUrl>` is deprecated in favor of `<PackageIcon>`.
In the next edition, I will add a warning about this and include a reference to the documentation. The tag names are documented in the **MSBuild Property** column in the table found at the following link:
I wrote, "To connect to a SQLite database, we just need to know the database filename, set using the parameter `Filename`."
In the next edition I will change this to, "To connect to a SQLite database, we just need to know the path to the database, set using the modern parameter named `Data Source` or the legacy parameter named `Filename`. The path can be relative to the current directory or an absolute path."
Throughout the rest of the book, I will replace the `Filename` parameter with `Data Source` for consistency with modern parameters. For example on pages 445, 453, 456, 464, 504, 541, and 547.
I recommend that you type from the print book or copy and paste long commands like this from the eBook into a plain text editor like Notepad. Then make sure that the whole command is properly formatted as a single line with correct spacing, before you then copy and paste it to the command-line. Copying and pasting directly from the eBook is likely to include newline characters and missing spaces and so on that break the command.
For convenience, here is the same command as a single line to make it easier to copy and paste:
In this section, I introduce the various technologies like Razor Pages, MVC, and Blazor that are included with ASP.NET Core.
In the next edition, I will add a section with a table summarizing the file types used by these technologies because they are similar but different and if the reader does not understand some subtle but important differences, it can cause much confusion when trying to implement their own projects.
A **Razor Layout** file like `_MyCustomLayout.cshtml` is identical to a **Razor View**. What makes it a layout is being set as the `Layout` property of another Razor file, as shown in the following code:
> **Convention**: The naming convention for special and shared Razor files like layouts and partial views is to prefix with an underscore `_`. For example, `_ViewStart.cshtml`, `_Layout.cshtml`, or `_Product.cshtml` (a partial view for rendering a product).
# Page 547 - Creating a class library for a Northwind database context
In Step 8, you write code to implement the `OnConfiguring` method so that it sets the Filename path to the SQLite database file correctly when running in both Visual Studio 2022 and at the command-line with Visual Studio Code, as shown in the following code:
In the next edition, it will be improved in two ways. First, by defining a string value once for the database name, and second, by checking that the database file exists and throwing an exception if it does not, as shown in the following code:
> After converting the relative path to an absolute path, you can set a breakpoint to more easily see where the database file is expected to be, or add a statement to log that path.
The throwing of the exception is important because if the database file is missing, then the SQLite database provider will create an empty database file, and so if you test connecting to it, it works! But if you query it then you will see an exception related to missing tables because it does not have any tables!
On page 553, we write some unit tests for this class and for SQLite the first test seems to work even when the path is actually wrong due to this issue. By adding code to throw an exception if the database file is missing, this test will now correctly fail.
In Step 11, in the `NorthwindContextExtensions.cs` file, we should also use a dynamically constructed string for the `AddNorthwindContext` method, as shown in the following code:
```cs
public static IServiceCollection AddNorthwindContext(
# Page 551 - Creating a class library for entity models using SQL Server
In Step 14, I tell the reader, "In the `Northwind.Common.DataContext.SqlServer` project, in `NorthwindContext.cs`, remove
the compiler warning about the connection string."
It would be an improvement to also replace the hard-coded string value used for the database connection string with a dynamically constructed string using the `SqlConnectionStringBuilder` class, as shown in the following code:
```cs
// At the top of the NorthwindContext.cs file.
using Microsoft.Data.SqlClient; // SqlConnectionStringBuilder
In Step 15, in the `NorthwindContextExtensions.cs` file, we should also use a dynamically constructed string using the `SqlConnectionStringBuilder` class, as shown in the following code:
```cs
// At the top of the NorthwindContextExtensions.cs file.
using Microsoft.Data.SqlClient; // SqlConnectionStringBuilder
```
The `AddNorthwindContext` method:
```cs
public static IServiceCollection AddNorthwindContext(
this IServiceCollection services,
string? connectionString = null)
{
if (connectionString == null)
{
SqlConnectionStringBuilder builder = new();
builder.DataSource = "."; // "ServerName\InstanceName" e.g. @".\sqlexpress"
builder.InitialCatalog = "Northwind";
builder.IntegratedSecurity = true;
builder.TrustServerCertificate = true;
builder.MultipleActiveResultSets = true;
builder.ConnectTimeout = 3; // Because we want to fail fast. Default is 15 seconds.
> **Warning!** *Razor Pages* are different from *Razor Views* (used in ASP.NET Core MVC) but they share the same file extension `.cshtml`. When creating a *Razor View*, do NOT use the `@page` directive!
In these sections you create two files named `Employees.cshtml` and `_Employee.cshtml`. I think the order that these files are created and the similarity of their names can confuse some readers. I will start this section with more explanation about what the reader is about to do i.e. create a Razor Page and a partial view, and that the Razor Page will use the partial view.
To make it clearer how they are related, what they do, and what their names mean, in the next edition, I will tell the reader to create the partial view that shows a single employee first and keep its name as `_Employee.cshtml`. Then I will tell the reader to create the Razor Page that uses that partial view but name it `EmployeesList.cshtml`.
This section starts with a description of the three parts of MVC. For views, I wrote, "**Views**: Razor files, that is, `.cshtml` files, that render data in view models into HTML web pages. Blazor uses the `.razor` file extension, but do not confuse them with Razor files!"
"**Views**: *Razor View* files, that is, `.cshtml` files, that render data in view models into HTML web pages. *Razor Views* are different from *Razor Pages* but they share the same file extension `.cshtml`. When creating a *Razor Page*, it must have the `@page` directive at the top of its file. When creating a *Razor View*, do NOT use the `@page` directive! If you do, the controller will not pass the model and it will be `null`, throwing a `NullReferenceException` when you try to access any of its members. Also note that Blazor uses the `.razor` file extension, but do not confuse them with *Razor View* or *Razor Page* files! To add even more confusion, Blazor can also use the `@page` directive to allow a Blazor component to act like a page!"
# Page 654 - Making controller action methods asynchronous
In an earlier task, you imported the `Microsoft.EntityFrameworkCore` namespace so that you could use the `Include` extension method. In Step 1, I tell you to use the `ToListAsync` method to implement the `Index` action method asynchronously. If you had not previously imported the `Microsoft.EntityFrameworkCore` namespace then you would have to import it now to use the `ToListAsync` method.
In the next edition, I will add a comment to make this more obvious, as shown in the following code:
```cs
using Microsoft.EntityFrameworkCore; // To use the Include and ToListAsync extension methods.
> Note: You could also use the simpler link format `https://localhost:5001/home/category/1` but then both the action method and the view filename must be just `Category` instead of `CategoryDetail`.
