field-injection.md

Field injection

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

using Shouldly;
using Pure.DI;

DI.Setup(nameof(Composition))
    .Bind<ICoffeeMachine>().To<CoffeeMachine>()
    .Bind<ISmartKitchen>().To<SmartKitchen>()

    // Composition root
    .Root<ISmartKitchen>("Kitchen");

var composition = new Composition();
var kitchen = composition.Kitchen;
kitchen.CoffeeMachine.ShouldBeOfType<CoffeeMachine>();

interface ICoffeeMachine;

class CoffeeMachine : ICoffeeMachine;

interface ISmartKitchen
{
    ICoffeeMachine? CoffeeMachine { get; }
}

class SmartKitchen : ISmartKitchen
{
    // The Dependency attribute specifies to perform an injection.
    // The DI will automatically assign a value to this field
    // when creating the SmartKitchen instance.
    [Dependency]
    public ICoffeeMachine? CoffeeMachineImpl;

    // Expose the injected dependency through a public property
    public ICoffeeMachine? CoffeeMachine => CoffeeMachineImpl;
}

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

The following partial class will be generated:

partial class Composition
{
  public ISmartKitchen Kitchen
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      var transientSmartKitchen293 = new SmartKitchen();
      transientSmartKitchen293.CoffeeMachineImpl = new CoffeeMachine();
      return transientSmartKitchen293;
    }
  }
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	CoffeeMachine --|> ICoffeeMachine
	SmartKitchen --|> ISmartKitchen
	Composition ..> SmartKitchen : ISmartKitchen Kitchen
	SmartKitchen *--  CoffeeMachine : ICoffeeMachine
	namespace Pure.DI.UsageTests.Basics.FieldInjectionScenario {
		class CoffeeMachine {
				<<class>>
			+CoffeeMachine()
		}
		class Composition {
		<<partial>>
		+ISmartKitchen Kitchen
		}
		class ICoffeeMachine {
			<<interface>>
		}
		class ISmartKitchen {
			<<interface>>
		}
		class SmartKitchen {
				<<class>>
			+SmartKitchen()
			+ICoffeeMachine CoffeeMachineImpl
		}
	}

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