Interview Question

What is the default lifetime of DbContext in Dependency Injection and why is it chosen as the default?

Answer

The default lifetime of DbContext in Entity Framework Core is Scoped. This means:

• A new instance is created once per request in web applications
• The same instance is shared within that request
• Different requests get different instances

// Default registration
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString));

// Equivalent to:
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString),
    ServiceLifetime.Scoped);

Why Scoped is the Default Choice

1. Resource Management

   • Automatic cleanup after each request
   • Prevents memory leaks from entity tracking
   • Efficient connection management

2. Thread Safety

   • Each request has its own DbContext
   • Safe for parallel request processing
   • Prevents concurrent access issues

Common Pitfall to Watch Out For

// ❌ WRONG: Never inject DbContext into Singleton services
public class SingletonService
{
    private readonly ApplicationDbContext _context; // This will cause issues!
    
    public SingletonService(ApplicationDbContext context)
    {
        _context = context;
    }
}

// ✅ CORRECT: Use scope creation in Singleton services
public class SingletonService
{
    private readonly IServiceProvider _serviceProvider;
    
    public SingletonService(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
    }
    
    public async Task DoWorkAsync()
    {
        using var scope = _serviceProvider.CreateScope();
        var context = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>();
        // Use context here
    }
}

Interview Tips 💡

• Emphasize that Scoped lifetime aligns with web request lifecycle
• Mention the importance of proper disposal in long-running operations
• Be ready to explain why Singleton lifetime should be avoided
• Know how to handle DbContext in background services

Common Follow-up Questions

1. How would you handle DbContext in a background service?
2. What are the implications of using Transient vs Scoped lifetime?
3. How do you properly dispose of DbContext when manually creating instances?