Question

I’m returning a null in my code: (the var cat line)

public class CategoryItemsViewModel
{
    public ICategoriesRepository categoriesRepository;

    public IEnumerable<Categories> GetCategories()
    {
        var cat = categoriesRepository.Categories;

        return cat;

    }
}

here is the interface:

namespace SportsStore.Domain.Abstract
{
    public interface ICategoriesRepository
    {
        IQueryable<Categories> Categories { get; }
        void SaveCategory(Categories category);
        void DeleteCategory(Categories category);
    }
}

here is the class:

namespace SportsStore.Domain.Entities
{
    public class Categories
    {
        [Key]
        public int CategoryID { get; set; }
        public string CategoryName { get; set; }
    }

}

What am I doing wrong?

Answer 1

What you have so far is fine – it’s just incomplete.

You don’t need a setter as someone else suggested either – in fact in this case it’s probably better not to have one.

You do need a concrete implementation of your interface ICategoriesRepository eg:

public class CategoriesRepository : ICategoriesRepository
{
    private readonly ModelContainer db= new ModelContainer();

    public IQueryable<Categories> Categories 
    { 
        get
        {
            return this.db.Categories;
        }
    }

    public void SaveCategory(Categories category)
    {
        // TODO
    }

    public void DeleteCategory(Categories category)
    {
        // TODO
    }
}

Then you will need to add a line to your viewmodel:

public class CategoryItemsViewModel
{
    public ICategoriesRepository categoriesRepository;

    public IEnumerable<Categories> GetCategories()
    {
        // This is to instantiate your repository.  It may be a better idea to do this
        // when it is declared, above.
        categoriesRepository = new CategoriesRepository();

        var cat = categoriesRepository.Categories;

        return cat;

    }
}