Build REST APIs in .NET 9: A Full Course for Beginners

Understanding REST APIs

• 💡 REST APIs are explained as a set of rules for how systems communicate over the web using HTTP methods like GET, POST, PUT, and DELETE.
• 🎯 They enable different applications (web, mobile, other software) to efficiently communicate with your app's data without directly interacting with databases or business logic.
• 🔑 The term REST stands for Representational State Transfer, and API stands for Application Programming Interface.

Setting Up Your First API Project

• 🚀 The course guides you through creating a new ASP.NET Core Web API project in Visual Studio using .NET 9.
• 📁 Key project files like Program.cs (entry point, middleware configuration) and appsettings.json (configuration, connection strings) are explained.
• ⚠️ A notable change in .NET 9 is the absence of Swagger UI by default, replaced by an HTTP file for testing endpoints.

Models and Controllers

• 🧠 Models represent the data structure of your application, typically defined as C# classes (e.g., a Book model with properties like ID, title, author, year published).
• 🛠️ Controllers specify how to interact with your REST API, handling different HTTP requests to get, modify, or delete data.
• 💡 A static list is used initially to hold book data, ensuring changes persist across HTTP requests within the same controller instance.

HTTP Methods and CRUD Operations

• 🔄 The course details how to implement HTTP GET (retrieve data), HTTP POST (add new data), HTTP PUT (update existing data), and HTTP DELETE (remove data) methods.
• ✅ Each method is demonstrated with corresponding attributes and return types, including status codes like 200 OK, 201 Created, 204 No Content, 400 Bad Request, and 404 Not Found.
• 🧪 API calls are tested using the built-in HTTP file, demonstrating how to send requests and interpret responses.

Connecting to SQL Server with Entity Framework Core

• 💾 For persistent data storage, the project connects to a SQL Server database using Entity Framework Core.
• 🏗️ A DbContext class is created to bridge the C# code with the database, and a DbSet for the Book model is defined.
• ⚙️ Configurations are set in appsettings.json with a connection string, and migrations are added using the Package Manager Console (add-migration, update-database).

Implementing CRUD with Database Persistence

• 💻 The static list is replaced by database interactions, and controller methods are made asynchronous to prevent blocking the application thread.
• 🔍 Data is accessed using context.Books.ToListAsync() for GET requests, context.Books.FindAsync(id) for specific resource retrieval, and context.Books.Add() for POST operations.
• 🔄 Updates are handled with context.Books.Update() (or by modifying properties directly) and deletions with context.Books.Remove(), all followed by context.SaveChangesAsync() to persist changes to the database.