Question

我正在使用NRules定义规则，并尝试在NRules基类中使用接口，但是出了一些问题，并且出现“没有为此对象定义无参数构造函数”错误。这是我的界面定义

{
    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开始加载组装时，我收到一个错误 MissingMethodException：没有为此对象定义无参数的构造函数。

 //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

如错误所述，您不能有一个规则，该规则的构造函数包含参数。

您还应该在规则定义内部解决依赖性，如NRules Wiki上的Rule Dependency所示。

因此，您的课程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));

        }

    }

如何将DbContext注入NRules类构造函数？

1 个答案: