Note
In Blazor Server applications, multiple threads could be used to handle requests from the same client connection. This can cause problems when using a service that is not thread-safe, such as the DbContext.
Quiz
What are the three main service lifetimes in C# and how do they differ?
- Transient: A new instance is created each time the service is requested.
- Scoped: An instance is created once per request scope.
- Singleton: Only one instance of the service is created the first time it is requested, and it is shared throughout the application’s lifetime.
What is the "Scope" of a service for ASP.NET Core API and Blazor Server applications?
- In an ASP.NET Core API application, the scope is typically per HTTP request. This means that a new instance of a scoped service is created for each incoming HTTP request and is shared within that request.
- In a Blazor Server application, the scope is per connection. This means that a new instance of a scoped service is created for each client connection and is shared within that connection.
When you call builder.Services.AddDbContext in ASP.NET Core, what is the default service lifetime for the DbContext?
- The default service lifetime for the DbContext is Scoped. This means that a new instance of the DbContext is created for each request scope (typically per HTTP request in an API application or per client connection in a Blazor Server application).
Why should we use the DbContextFactory instead of directly injecting the DbContext for Blazor Server applications? And what are some things that you should be aware of when using it?
- In Blazor Server applications, the scope is per connection, which means that if you inject the
DbContextdirectly, it will be shared across all requests from that connection. TheDbContextis not thread-safe, and is designed to be short-lived. If you do try to use the sameDbContextinstance, you may encounter anInvalidOperationException. - When using the
DbContextFactory, you should be aware that theDbContextFactoryitself is a singleton service and managed by the DI container, however theDbContextinstances it creates are not managed by the DI container. Therefore, you should useusing varto dispose of them.