Entity Framework DB Context null when using Autofac IOC

Question

I'm trying to move the query logic out of my controllers. My problem is context is null and is throwing an exception in my concrete class PetRepository when I try and get a list of pets.

In the interface:

    public interface IPetRepository
    {
    List<Pet> GetAllPets();   
    PetStoreContext context { get; set; }
    }

In the concrete implementation:

public class PetRepository : IPetRepository
{
    public PetStoreContext context { get; set; }

    public List<Pet> GetAllPets()
    {
        return context.Pet.ToList(); //this line throws a null exception
    }
 }

In my controller I'm using constructor injection:

public class PetsController : BaseController
{
    private IPetRepository _petRepository;

    public PetsController(IPetRepository petRepository)
    {
        _petRepository = petRepository;
    }
 }

Then my action result

public ActionResult Index()
    {            
        var model = new PetListing()
        {
            Pets = _petRepository.GetAllPets()
         }
       return View(model);
     }

And finally I am just doing a simple mapping with autofac.

  private void RegisterAutoFac()
    {
        var builder = new ContainerBuilder();
        builder.RegisterControllers(Assembly.GetExecutingAssembly());
        builder.RegisterSource(new ViewRegistrationSource());

        builder.RegisterType<PetRepository>().As<IPetRepository>();

        var container = builder.Build();

        DependencyResolver.SetResolver(new AutofacDependencyResolver(container));

    }

If I use the same lines of code in my controller directly then I get a list of pets back from the DB e.g

public ActionResult Index()
{
 public PetStoreContext context = new PetStoreContext();    
return View(context.Pet.ToList());
}

Lockdowne · Accepted Answer · 2017-06-24 08:07:02Z

2

context is a property not being set, instead let IoC instantiate it for you by injecting it into your repo:

public class PetRepository : IPetRepository
{
    private readonly PetStoreContext _context;

    public PetRepository(PetStoreContext context)
    {
        _context = context;
    }

    public List<Pet> GetAllPets()
    {
        return _context.Pet.ToList();
    }
 }

answered Jun 24, 2017 at 8:07

Lockdowne

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3 Comments

JKerny Over a year ago

Thanks. I'm new to IOC. Is there another piece to the puzzle. Now I'm getting one of those confusing IOC run time errors when I call my controller : None of the constructors found with 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type 'PetStore.Repository.PetRepository' can be invoked with the available services and parameters: Cannot resolve parameter 'PetStore.PetStore.DAL.Context.PetStoreContext context' of constructor 'Void .ctor(PetStore.PetStore.DAL.Context.PetStoreContext)'.

Lockdowne Over a year ago

It looks like you will need to register the context with Autofac stackoverflow.com/questions/29560294/…

JKerny Over a year ago

Your original answer was correct. I wasn't instantiating context. I resolved this by making a BaseRepository interface with a concrete implementation that newed up context. Then I used IOC to pass the BaseRepo into the PetRepo constructor and Bob's you uncle. Thanks again

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