Dependency Injection in .NET: Core Concepts and Implementation

8 min read•February 9, 2026
Dependency Injection .NETDI .NET Core.NET service lifetimesTransient Scoped Singleton.NET IoC containerConstructor injection C#.NET best practicesLoose coupling .NET

# Dependency Injection in .NET

Dependency Injection (DI) is central to ASP.NET Core architecture. Used correctly, it keeps modules decoupled, testable, and easier to evolve.

Understanding Lifetimes

Transient

New instance every resolution. Good for lightweight, stateless services.

Scoped

One instance per request scope. Ideal for request-bound services and DbContext.

Singleton

One instance for app lifetime. Use only for thread-safe services without scoped dependencies.

Practical Registration Patterns

  • Register by interface for clear boundaries
  • Keep composition root explicit in startup/bootstrap code
  • Use factory registrations only when object creation truly needs runtime branching
  • Prefer options pattern for configuration-heavy services

    • Common DI Mistakes

  • Captive dependency: singleton depending on scoped service
  • Service locator anti-pattern in business code
  • Over-registering classes that should remain internal implementation details
  • Treating DI as a substitute for architecture decisions

    • Testing Benefits

  • Constructor injection simplifies mocks/stubs
  • Clear dependencies reduce hidden side effects
  • Integration tests can swap infrastructure registrations cleanly

    • Conclusion

    Good DI is not just container usage, it is explicit dependency design. That design directly impacts maintainability, testability, and change safety.

    I can review your registration graph and highlight lifetime risks.

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