diff --git a/docs/errata/README.md b/docs/errata/README.md index 2e24f2b..8bc47d4 100644 --- a/docs/errata/README.md +++ b/docs/errata/README.md @@ -2,7 +2,7 @@ If you find any mistakes in the seventh edition, *C# 11 and .NET 7 - Modern Cross-Platform Development Fundamentals*, or 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. -[**Errata** (27 items)](errata.md): Typos, tool user interface changes, or mistakes in code that would cause a compilation error that prevents a successful build. +[**Errata** (29 items)](errata.md): Typos, tool user interface changes, or mistakes in code that would cause a compilation error that prevents a successful build. [**Improvements** (5 items)](improvements.md): Changes to text or code that would improve the content. These are optional. diff --git a/docs/errata/errata.md b/docs/errata/errata.md index d0da754..1afa575 100644 --- a/docs/errata/errata.md +++ b/docs/errata/errata.md @@ -1,4 +1,4 @@ -**Errata** (27 items) +**Errata** (29 items) 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. @@ -27,12 +27,15 @@ If you find any mistakes, then please [raise an issue in this repository](https: - [Page 399 - Managing directories](#page-399---managing-directories) - [Page 412 - Compressing streams](#page-412---compressing-streams) - [Page 477 - Inserting entities](#page-477---inserting-entities) +- [Page 548 - Creating a class library for a Northwind database context](#page-548---creating-a-class-library-for-a-northwind-database-context) +- [Page 551 - Creating a class library for entity models using SQL Server](#page-551---creating-a-class-library-for-entity-models-using-sql-server) - [Page 627 - Defining a typed view](#page-627---defining-a-typed-view) - [Page 631 - Passing parameters using a route value](#page-631---passing-parameters-using-a-route-value) - [Page 641 - Enabling role management and creating a role programmatically](#page-641---enabling-role-management-and-creating-a-role-programmatically) - [Page 649 - Varying cached data by query string](#page-649---varying-cached-data-by-query-string) - [Page 707 - Reviewing the Blazor Server project template](#page-707---reviewing-the-blazor-server-project-template) - [Page 733 - Building customer create, edit, and delete components](#page-733---building-customer-create-edit-and-delete-components) +- [Page 724 - Getting entities into a component](#page-724---getting-entities-into-a-component) # Page 4, 8 - Pros and cons of the .NET Interactive Notebooks extension, Downloading and installing Visual Studio Code @@ -280,6 +283,84 @@ It should use the method signature that allows multiple `productIds` to be highl 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: +```cs +using Microsoft.EntityFrameworkCore; // UseSqlite +using Microsoft.Extensions.DependencyInjection; // IServiceCollection + +namespace Packt.Shared; + +public static class NorthwindContextExtensions { + /// + /// Adds NorthwindContext to the specified IServiceCollection. Uses the Sqlite database provider. + /// + /// + /// Set to override the default of ".." + /// Set to override the default of "Northwind.db" + /// An IServiceCollection that can be used to add more services. + public static IServiceCollection AddNorthwindContext( + this IServiceCollection services, + string relativePath = "..", + string databaseFilename = "Northwind.db") { + + string databasePath = Path.Combine(relativePath, databaseFilename); + + services.AddDbContext(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 with multiple threads. + 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: +```cs +using Microsoft.EntityFrameworkCore; // UseSqlServer +using Microsoft.Extensions.DependencyInjection; // IServiceCollection + +namespace Packt.Shared; + +public static class NorthwindContextExtensions { + /// + /// Adds NorthwindContext to the specified IServiceCollection. Uses the SqlServer database provider. + /// + /// + /// Set to override the default. + /// An IServiceCollection that can be used to add more services. + public static IServiceCollection AddNorthwindContext( + this IServiceCollection services, + string connectionString = "Data Source=.;Initial Catalog=Northwind;" + + "Integrated Security=true;MultipleActiveResultsets=true;Encrypt=false") { + + services.AddDbContext(options => { + options.UseSqlServer(connectionString); + options.LogTo(Console.WriteLine, + new[] { Microsoft.EntityFrameworkCore.Diagnostics.RelationalEventId.CommandExecuting }); + }, // Register with a transient lifetime to avoid concurrency issues with multiple threads. + contextLifetime: ServiceLifetime.Transient, optionsLifetime: ServiceLifetime.Transient); + + return services; + } +} +``` + # Page 627 - Defining a typed view > Thanks to [Chadwick Geyser](https://github.com/chadwickgeyser) for raising this [issue on 4 December 2022](https://github.com/markjprice/cs11dotnet7/issues/6). @@ -407,3 +488,17 @@ private async Task Update() navigation.NavigateTo("customers"); } ``` + +# Page 724 - Getting entities into a component + +In Step 4, you write a statement to call an extension method that you previously created in Chapter 12, as shown in the following code: +```cs +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 instance is shared between multiple threads running on the server. This can cause concurrency issues as described here: +https://learn.microsoft.com/en-gb/ef/core/dbcontext-configuration/#implicitly-sharing-dbcontext-instances-via-dependency-injection + +To fix this issue, please make the changes shown in the following items: +- [Page 548 - Creating a class library for a Northwind database context](#page-548---creating-a-class-library-for-a-northwind-database-context) +- [Page 551 - Creating a class library for entity models using SQL Server](#page-551---creating-a-class-library-for-entity-models-using-sql-server)