property-injection.md

Property injection

To use dependency injection on a property, make sure the property is writable and simply add the Ordinal attribute to that property, specifying the ordinal that will be used to determine the injection order:

using Shouldly;
using Pure.DI;

DI.Setup(nameof(Composition))
    .Bind<ILogger>().To<ConsoleLogger>()
    .Bind<IService>().To<Service>()

    // Composition root
    .Root<IService>("MyService");

var composition = new Composition();
var service = composition.MyService;
service.Logger.ShouldBeOfType<ConsoleLogger>();

interface ILogger;

class ConsoleLogger : ILogger;

interface IService
{
    ILogger? Logger { get; }
}

class Service : IService
{
    // The Dependency attribute specifies to perform an injection,
    // the integer value in the argument specifies
    // the ordinal of injection.
    // Usually, property injection is used for optional dependencies.
    [Dependency] public ILogger? Logger { get; set; }
}

Running this code sample locally

• Make sure you have the .NET SDK 10.0 or later installed

dotnet --list-sdk

• Create a net10.0 (or later) console application

dotnet new console -n Sample

• Add references to the NuGet packages
  • Pure.DI
  • Shouldly

dotnet add package Pure.DI
dotnet add package Shouldly

• Copy the example code into the Program.cs file

You are ready to run the example 🚀

dotnet run

The key points are:

• The property must be writable
• The Dependency (or Ordinal) attribute is used to mark the property for injection
• The DI automatically injects the dependency when resolving the object graph

The following partial class will be generated:

partial class Composition
{
  public IService MyService
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      var transientService316 = new Service();
      transientService316.Logger = new ConsoleLogger();
      return transientService316;
    }
  }
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	ConsoleLogger --|> ILogger
	Service --|> IService
	Composition ..> Service : IService MyService
	Service *--  ConsoleLogger : ILogger
	namespace Pure.DI.UsageTests.Basics.PropertyInjectionScenario {
		class Composition {
		<<partial>>
		+IService MyService
		}
		class ConsoleLogger {
				<<class>>
			+ConsoleLogger()
		}
		class ILogger {
			<<interface>>
		}
		class IService {
			<<interface>>
		}
		class Service {
				<<class>>
			+Service()
			+ILogger Logger
		}
	}

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