Property Injection in Asp.Net Core

Question

I am trying to port an asp.net application to asp.net core. I have property injection (using ninject) on my UnitOfWork implementation like this.

[Inject]
pu         


        

Answer 1

Is there a way to achieve the same functionality using build in DI on .net core?

No, but here is how you can create your own [inject] attributes with the help of autofac's property injection mecanism.

First Create your own InjectAttribute:

[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
public class InjectAttribute : Attribute
{
  public InjectAttribute() : base() { }
}

Then create your own InjectPropertySelector that uses reflection to check for properties marked with [inject]:

public class InjectPropertySelector : DefaultPropertySelector
{
  public InjectPropertySelector(bool preserveSetValues) : base(preserveSetValues)
  { }

  public override bool InjectProperty(PropertyInfo propertyInfo, object instance)
  {
    var attr = propertyInfo.GetCustomAttribute(inherit: true);
    return attr != null && propertyInfo.CanWrite
            && (!PreserveSetValues
            || (propertyInfo.CanRead && propertyInfo.GetValue(instance, null) == null));
  }
}

Then use your selector in your ConfigureServices where you wire up your AutofacServiceProvider:

public class Startup
{
  public IServiceProvider ConfigureServices(IServiceCollection services)
  {
    var builder = new ContainerBuilder();
    builder.Populate(services);

    // use your property selector to discover the properties marked with [inject]
    builder.RegisterType().PropertiesAutowired((new InjectablePropertySelector(true)););

    this.ApplicationContainer = builder.Build();
    return new AutofacServiceProvider(this.ApplicationContainer);
  }
}

Finally in your service you can now use [inject]:

public class MyServiceX 
{
    [Inject]
    public IOrderRepository OrderRepository { get; set; }
    [Inject]
    public ICustomerRepository CustomerRepository { get; set; }
}

You surely can take this solution even further, e.g. by using an attribute for specifying your service's lifecycle above your service's class definition...

[Injectable(LifetimeScope.SingleInstance)]
public class IOrderRepository

...and then checking for this attribute when configuring your services via autofac. But this would go beyond the scope of this answer.