The dotnet CLI (Command-Line Interface) allows you to install NuGet packages from a local feed or folder. It provides the dotnet add package command, which supports specifying package sources. This is particularly useful when working in an offline environment or when you want to use custom package sources.

ASP.NET Core introduces a built-in Dependency Injection (DI) system, which was not part of traditional ASP.NET. In the past, developers often relied on third-party libraries for DI, but ASP.NET Core brings this critical feature into the framework, making it easier to manage dependencies in your applications.

The "Startup.cs" file in an ASP.NET Core project plays a crucial role in configuring middleware and services for the application. It defines how the application will handle requests, set up routing, and configure various components like authentication, logging, and dependency injection. It's essentially the entry point for configuring the application's behavior.

To make a tag helper available across all your Razor views without adding its namespace to each view individually, you can use the element in the _ViewImports.cshtml file. This centralizes tag helper configuration for the entire directory, making it accessible to all views within that directory.

For reusability, developers can create Razor Components, which are similar to partial views but with more logic encapsulation. Razor Components encapsulate both the UI and the code, making them highly reusable and self-contained.

When you see a generic "An error occurred" message during development, it might be because Debug Mode is disabled in your ASP.NET Core application. Enabling Debug Mode provides detailed error information to help developers diagnose issues.

ASP.NET Core's configuration system allows you to access configuration values using a key/value API. This system can be configured using multiple configuration sources (e.g., JSON, XML, environment variables, command-line arguments) to provide flexibility in managing application settings.

ASP.NET Core's approach to preventing Cross-Site Request Forgery (CSRF) attacks involves using a token named CSRF (Cross-Site Request Forgery). This token is generated for each user session and is included in requests to ensure that the request originated from the same site, thereby preventing malicious actions from other domains. It's an essential security measure in web applications.

For securing APIs in ASP.NET Core, token-based authentication is recommended. Token-based authentication, often using technologies like OAuth 2.0 or JWT (JSON Web Tokens), provides a secure and scalable way to authenticate and authorize users for API access. It's widely adopted for modern API security scenarios.

After adding the new field to the model class, you should run the dotnet ef migrations add command to generate a new migration. This migration will contain the necessary changes to update the database schema. Manually updating the schema is not recommended as it can lead to inconsistencies.

In Entity Framework Core, developers can use the ExecuteSqlCommand method inside the DbContext to execute arbitrary SQL commands. This is especially useful for advanced configurations, data migrations, or when you need to perform database operations that are not supported by LINQ.

The primary purpose of the Startup.cs file is to configure the application's request handling pipeline. It defines how HTTP requests are processed, which controllers and actions handle them, and how various middleware components are configured. Additionally, it sets up services, defines routes, and performs other initialization tasks necessary for the application to run.