Dependency Injection

Dependency Injection and DbContext in ASP.NET Core

**What is Dependency Injection (DI)?

• Definition: A design pattern that reduces coupling between components, increasing maintainability and testability.
• Core Principle: Instead of instantiating objects directly in a class, they are passed as parameters to constructors or methods.
• Benefits:
  • Flexible object creation and management.
  • Simplifies testing of individual components.
  • Enables adherence to SOLID principles (e.g., the Dependency Inversion principle).

DI in ASP.NET Core

• ASP.NET Core has a built-in dependency injection container.
• The container manages the lifetime and dependencies of services registered during application startup.
• Services can be registered in the Program.cs file.

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Non-DI Example

• In a non-DI scenario:
  • A class (e.g., MyController) directly instantiates a dependency (e.g., MyService).
  • Any changes to MyService (e.g., renaming or replacing it) require modifying all the consuming classes.

DI Example

• In a DI scenario:
  • The dependency (e.g., MyService) is injected into the consumer (e.g., MyController) via the constructor or a method.
  • The implementation of the dependency is defined in one place (Program.cs), making it easier to manage changes.

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Steps to Inject DbContext in ASP.NET Core

1. Open Program.cs.

2. Register the DbContext Class:

   builder.Services.AddDbContext<TRWalksDbContext>(options =>
       options.UseSqlServer(builder.Configuration.GetConnectionString("TRWalksConnectionString")));
   
   

   • AddDbContext: Adds the DbContext to the DI container.
   • UseSqlServer: Configures Entity Framework Core to use SQL Server.
   • Connection String: Retrieved from appsettings.json using builder.Configuration.GetConnectionString.

3. Configure Connection String in appsettings.json:

   "ConnectionStrings": {
     "TRWalksConnectionString": "Server=<YourServerName>;Database=TRWalksDB;Trusted_Connection=True;TrustServerCertificate=True;"
   }
   
   

4. Verify DI Registration:

   • Once registered, the DbContext can be injected into controllers or repositories.

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Outcome

• The DbContext is managed by ASP.NET Core's DI container.
• It can be used throughout the application in controllers or repositories without manual instantiation.
• Simplifies database interaction and enables flexibility for changes.