如何在NRules类构造函数中注入DbContext？

Question

我正在使用NRules来定义规则，并试图在NRules基类中使用接口，但是发生了一些错误，我得到了“没有为这个对象定义无参数构造函数”的错误。下面是我的接口定义

{
    public interface ICalcDiscount
    {
        public void ApplyPoint(int point);
    }
    public class CalcDiscount:ICalcDiscount
    {
        private readonly UniContext _context;

       public CalcPoint(UniContext context)
        {
            _context = context;

        }

        public  void ApplyDiscount(int d)
        {
           _context.Discount.Add(new Discount{ CustomerId = 1, d= d});
           _context.SaveChanges();
        }
    }
}

NRule类

 public class PreferredCustomerDiscountRule : Rule
    {
        private readonly ICalcDiscount _d;

        public PreferredCustomerDiscountRule(ICalcDiscount d)
        {
            _d = d;
        }
        public override void Define()
        {
            Book book = null;


            When()

                .Match(() => book);


            Then()
                .Do(ctx => _c.ApplyDiscount(10));

        }

    }

当NRules开始加载程序集MissingMethodException时，我收到一个错误:没有为此对象定义无参数构造函数。

 //Load rules
    var repository = new RuleRepository();
    repository.Load(x => x.From(typeof(PreferredCustomerDiscountRule).Assembly));//problem is here!
 //Compile rules
    var factory = repository.Compile();

Answer 1

正如错误所说，您不能有一个包含参数的构造函数的规则。

您还应该解析规则定义中的依赖项，如NRules维基上的Rule Dependency所示。

因此，您的类应该类似于以下内容：

public class PreferredCustomerDiscountRule : Rule
    {
        public override void Define()
        {
            Book book = null;
            ICalcDiscount discountService = null;

            Dependency()
                .Resolve(() => discountService);

            When()
                .Match(() => book);


            Then()
                .Do(_ => discountService.ApplyDiscount(10));

        }

    }