Dependency Injection Lifetimes

ASP.NET Core provides three main lifetimes for services registered in the Dependency Injection (DI) container.
Each lifetime defines how long an instance of a service lives and how it is shared.

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Transient

• A new instance is created every time the service is requested
• Suitable for:
  • Lightweight classes
  • Stateless services
• ❌ Not suitable for database connections
• Example registration:

  services.AddTransient<IEmailService, EmailService>();
  

Scoped

• One instance is created per HTTP request
• The same instance is shared within that request
• Suitable for:
  • Web requests
  • DbContext
  • Unit of Work pattern
• ✅ Recommended for business logic

• Example registration:

  services.AddScoped<IOrderService, OrderService>();
  

Singleton

• Only one instance for the whole application lifetime
• Shared across all users and requests
• Suitable for:
  • Caching
  • Configuration
  • Logging
• ⚠️ Must be thread-safe

• Example registration:

  services.AddSingleton<ICacheService, CacheService>();
  

• Golden Rule

  • A service with a longer lifetime must NOT depend on a service with a shorter lifetime. (This can cause memory leaks or unpredictable behavior)
  • ❌ Invalid dependencies:
    • Singleton → Scoped
    • Singleton → Transient

• Quick Guide

  • Helper / Utility code → Transient
  • Business Logic → Scoped
  • Database Access (DbContext) → Scoped
  • Cache / Configuration → Singleton