ASP.NET Core Dependency Injection and Lifetime Selection

Dependency injection is not framework magic. It separates object creation from object usage. The risky part is choosing the wrong lifetime.

flowchart TB
    A["Application startup"] --> B["Singleton"]
    C["Each HTTP request"] --> D["Scoped"]
    E["Each resolve"] --> F["Transient"]
    B --> G["Must be thread-safe"]
    D --> H["Business service / DbContext"]
    F --> I["Lightweight stateless object"]

Engineering Scenario

DbContext is usually scoped because it belongs to one request or unit of work. Injecting it into a singleton leaks request-level state into global lifetime.

Best Practices

• Start with Scoped for business services.
• Singleton must be stateless or thread-safe.
• Use Transient for lightweight objects.
• Design lifetime and disposal together.