Handling circular dependencies in .NET can often be challenging and may lead to a cumbersome refactoring process. SmartInject is a versatile NuGet package designed to simplify this task, allowing developers to effortlessly manage and resolve circular dependencies through lazy loading. This article provides an insightful overview of how SmartInject operates, offering a practical solution to a common problem, without the need for extensive code restructuring.
Introduction
Dependency Injection (DI) is a common technique to achieve Inversion of Control (IoC) between classes and their dependencies. However, developers may encounter a System.InvalidOperationException
related to circular dependencies. This article introduces a convenient solution: SmartInject, a NuGet package that simplifies dependency injection in .NET by employing lazy loading to handle circular dependencies. Check it out on NuGet.
Background
When dealing with classes that depend on each other, a circular dependency is created, leading to an infinite loop during object instantiation. This scenario typically requires refactoring to resolve, but SmartInject provides an efficient workaround by implementing lazy loading. With SmartInject, dependencies are resolved in a deferred manner, eliminating the circular dependency issue without the need for major code restructuring.
Using the Code
Consider a scenario where Something
depends on SomethingElse
, and vice versa:
public class Something
{
public Something(SomethingElse somethingElse) { }
}
public class SomethingElse
{
public SomethingElse(Something something) { }
}
This typical arrangement would throw a System.InvalidOperationException
due to a circular dependency. With SmartInject, you can restructure the code as follows:
public class Something : ISomething
{
private readonly Lazy<ISomethingElse> _somethingElse;
public Something(Lazy<ISomethingElse> somethingElse)
{
_somethingElse = somethingElse;
}
}
public class SomethingElse : ISomethingElse
{
private readonly Lazy<ISomething> _something;
public SomethingElse(Lazy<ISomething> something)
{
_something = something;
}
}
With the Lazy<T>
class, SmartInject ensures that instances are not created until they are needed, effectively breaking the circular dependency loop. Services can be registered using SmartInject’s specialized methods:
builder.Services.AddLazySingleton<ISomething, Something>();
SmartInject also supports other service lifetimes, providing flexibility for various application needs. You can choose from the following registration methods, based on your requirements:
builder.Services.AddLazySingleton<ISomething, Something>();
builder.Services.AddLazyTransient<ISomething, Something>();
builder.Services.AddLazyScoped<ISomething, Something>();
Each method corresponds to a different service lifetime, allowing you to select the most appropriate one for your application's architecture and performance needs. For additional details, explore the SmartInject source code on GitHub.
Points of Interest
The SmartInject package offers an elegant solution to handle circular dependencies without requiring significant code restructuring. It introduces a deferred instantiation approach, improving the application's startup performance while integrating seamlessly with the .NET DI framework.
History
- 3rd October, 2023: This is the initial publication of this trick. Future updates and improvements to the SmartInject package or related tricks will be documented in subsequent revisions.