abp-dependency-injection

ABP Dependency Injection Skill

Trigger

User asks about dependency injection, DI, ITransientDependency, ISingletonDependency, IScopedDependency, [Dependency] attribute, [ExposeServices] attribute, auto service registration, or Autofac in ABP Framework.

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Core Concepts

ABP's DI system is built on Microsoft's Microsoft.Extensions.DependencyInjection with:

• Conventional (automatic) registration — Classes registered by convention
• Dependency interfaces — ITransientDependency, ISingletonDependency, IScopedDependency
• Dependency attribute — [Dependency] for fine-grained control
• ExposeServices attribute — [ExposeServices] to control exposed interfaces
• Autofac integration — Required for dynamic proxying (included in startup templates)

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Conventional Registration

ABP automatically registers all services in your assembly. No manual registration needed.

// This class is auto-registered as transient
public class TaxCalculator : ITransientDependency
{
    public decimal Calculate(TaxInput input) { ... }
}

Disable Auto Registration

public class BlogModule : AbpModule
{
    public BlogModule()
    {
        SkipAutoServiceRegistration = true;
    }

    public override void ConfigureServices(ServiceConfigurationContext context)
    {
        // Manual registration
        context.Services.AddAssemblyOf<BlogModule>();
    }
}

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Dependency Interfaces

Implement these interfaces for automatic registration:

Interface	Lifetime	Use Case
ITransientDependency	Transient	Default for most services
ISingletonDependency	Singleton	Shared state, caches
IScopedDependency	Scoped	Per-request state

public class TaxCalculator : ITransientDependency { }
public class CacheService : ISingletonDependency { }
public class RequestTracker : IScopedDependency { }

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Dependency Attribute

More control over registration:

[Dependency(ServiceLifetime.Transient, ReplaceServices = true)]
public class TaxCalculator
{
}

Properties

Property	Type	Purpose
Lifetime	ServiceLifetime	Transient, Singleton, or Scoped
TryRegister	bool	Register only if not already registered
ReplaceServices	bool	Replace existing registration

[Dependency(ServiceLifetime.Singleton, TryRegister = true)]
public class MyCacheService { }

[Dependency(ServiceLifetime.Transient, ReplaceServices = true)]
public class OverridingService { }

[Dependency] has higher priority than dependency interfaces if Lifetime is defined.

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ExposeServices Attribute

Control which interfaces a class exposes:

[ExposeServices(typeof(ITaxCalculator))]
public class TaxCalculator : ICalculator, ITaxCalculator, ICanCalculate, ITransientDependency
{
}

• Only ITaxCalculator can be injected
• TaxCalculator, ICalculator, ICanCalculate are NOT injectable

Expose Multiple Services

[ExposeServices(typeof(ITaxCalculator), typeof(ICalculator))]
public class TaxCalculator : ICalculator, ITaxCalculator, ITransientDependency
{
}

Expose All (default behavior)

Without [ExposeServices], all implemented interfaces are exposed:

public class TaxCalculator : ICalculator, ITaxCalculator, ITransientDependency
{
}
// Can inject: TaxCalculator, ICalculator, ITaxCalculator

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Combining Attributes and Interfaces

[Dependency(ReplaceServices = true)]
[ExposeServices(typeof(ITaxCalculator))]
public class TaxCalculator : ITaxCalculator, ITransientDependency
{
}

• ReplaceServices = true → replaces existing ITaxCalculator registration
• ExposeServices → only ITaxCalculator can be injected
• ITransientDependency → transient lifetime (overridden by [Dependency] if specified)

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Inherently Registered Types

These types are automatically registered by ABP:

• AbpModule implementations
• Controllers, PageModels
• Domain services, Application services
• Repositories (via EF Core / MongoDB modules)

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Autofac Integration

ABP requires a DI provider that supports dynamic proxying for:

• Unit of Work interception
• Validation interception
• Authorization interception
• Auditing interception
• Feature checking

Startup templates come with Autofac pre-installed.

Manual Autofac Setup

dotnet add package Volo.Abp.Autofac

[DependsOn(typeof(AbpAutofacModule))]
public class MyModule : AbpModule { }

In Program.cs:

builder.Host.UseAutofac();

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Property Injection

ABP supports property injection via Autofac:

public class MyService : ITransientDependency
{
    public IEmailSender EmailSender { get; set; } // Property injected

    private readonly IRepository<MyEntity> _repository; // Constructor injected

    public MyService(IRepository<MyEntity> repository)
    {
        _repository = repository;
    }
}

Constructor injection is preferred. Property injection is useful for optional dependencies.

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Resolving Services

Constructor Injection (Recommended)

public class MyService : ITransientDependency
{
    private readonly IEmailSender _emailSender;

    public MyService(IEmailSender emailSender)
    {
        _emailSender = emailSender;
    }
}

Property Injection

public class MyService : ITransientDependency
{
    public IEmailSender EmailSender { get; set; }
}

Manual Resolution (Avoid When Possible)

public class MyService : ITransientDependency
{
    private readonly IServiceProvider _serviceProvider;

    public MyService(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
    }

    public void DoWork()
    {
        var emailSender = _serviceProvider.GetRequiredService<IEmailSender>();
    }
}

Lazy Service Resolution (LazyServiceProvider)

Instead of manual resolution via IServiceProvider, ABP's lazy service resolution is preferred. ABP base classes (ApplicationService, DomainService, AbpController) come with a LazyServiceProvider property out of the box — it prevents constructor bloat when you have optional or numerous dependencies:

public class BookAppService : ApplicationService
{
    // No need to inject — comes from the base class
    private IEmailSender EmailSender => LazyServiceProvider.LazyGetRequiredService<IEmailSender>();

    public async Task NotifyAsync()
    {
        await EmailSender.SendAsync("to@x.com", "Subject", "Body");
    }
}

In non-base-class services, inject ITransientCachedServiceProvider (the old IAbpLazyServiceProvider is for backward compatibility and may be removed in the future):

public class MyService : ITransientDependency
{
    private readonly ITransientCachedServiceProvider _serviceProvider;
    public MyService(ITransientCachedServiceProvider serviceProvider)
        => _serviceProvider = serviceProvider;

    private IEmailSender EmailSender => _serviceProvider.GetRequiredService<IEmailSender>();
}

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Best Practices

1. Use conventional registration — implement ITransientDependency (default)
2. Prefer constructor injection — explicit dependencies, easier to test
3. Use [Dependency(ReplaceServices = true)] to override framework services
4. Use [ExposeServices] to limit exposed interfaces
5. Use IScopedDependency for per-request state (HTTP context, etc.)
6. Use ISingletonDependency only for stateless services or caches
7. Don't use service locator pattern — avoid IServiceProvider resolution
8. Keep services focused — single responsibility, small interfaces
9. Use Autofac — required for dynamic proxying (interceptors, UOW, validation)
10. Skip auto-registration only when you need full control over DI setup

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Common Patterns

Repository Injection

public class BookAppService : ApplicationService, IBookAppService
{
    private readonly IRepository<Book, Guid> _bookRepository;

    public BookAppService(IRepository<Book, Guid> bookRepository)
    {
        _bookRepository = bookRepository;
    }
}

Domain Service

public class BookManager : DomainService, ITransientDependency
{
    private readonly IRepository<Book, Guid> _bookRepository;

    public BookManager(IRepository<Book, Guid> bookRepository)
    {
        _bookRepository = bookRepository;
    }

    public async Task<Book> CreateAsync(CreateBookDto input)
    {
        var book = new Book { Name = input.Name };
        return await _bookRepository.InsertAsync(book);
    }
}

Override Framework Service

[Dependency(ReplaceServices = true)]
public class MyCustomEmailSender : IEmailSender, ITransientDependency
{
    public async Task SendAsync(string to, string subject, string body)
    {
        // Custom email logic
    }
}

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Related

• Framework Core — base classes, module system, configuration
• Modularity — module-based DI registration, [DependsOn]
• DDD — application/domain service registration
• Autofac — DI container with dynamic proxying support
• ABP Docs: https://abp.io/docs/latest/framework/fundamentals/dependency-injection