如何模拟自定义 ValueResolver 构造函数参数

Question

我在 .NET Core 中有一个项目，我正在使用 AutoMapper 在我的类型之间进行映射。但我遇到了一个问题，我想模拟自定义值解析器的参数。我创建了虚拟示例来显示问题：

假设我有一个 ValueResolver，它需要访问数据库来解析给定的成员：

public class NumberProfile : Profile
{
    public NumberProfile()
    {
        CreateMap<NumberModel, NumberDto>()
            .ForMember(dest => dest.Number, opt => opt.MapFrom<NumberValueResolver>());
    }
}

public class NumberValueResolver : IValueResolver<NumberModel, NumberDto, int>
{
    private readonly IRepository _repository;

    public NumberValueResolver(IRepository repository)
    {
        _repository = repository;
    }

    public int Resolve(NumberModel source, NumberDto destination, int destMember, ResolutionContext context)
    {
        return _repository.GetNumber().Number + 3;
    }
}

让我们想象一下，Resolve 方法中有逻辑需要测试，我想模拟存储库以便能够测试它。这是我在测试中尝试过的

var repositoryMock = new Mock<IRepository>();
repositoryMock.Setup(s => s.GetNumber()).Returns(new NumberModel { Number = 3 });

var mapper = new MapperConfiguration(mc =>
{
    mc.AddProfile<NumberProfile>();
    mc.ConstructServicesUsing(s => new NumberValueResolver(repositoryMock.Object));
});

var service = new Service(repositoryMock.Object, mapper.CreateMapper());

然后我调用服务上的一个方法来触发映射。这个案例很好，可以工作并且测试通过。当我添加另一个 ValueResolver 时，问题就出现了。

public class NumberProfile : Profile
{
    public NumberProfile()
    {
        CreateMap<NumberModel, NumberDto>()
            .ForMember(dest => dest.Number, opt => opt.MapFrom<NumberValueResolver>())
            .ForMember(dest => dest.AnotherNumber, opt => opt.MapFrom<AnotherNumberValueResolver>());
    }
}

public class NumberValueResolver : IValueResolver<NumberModel, NumberDto, int>
{
    private readonly IRepository _repository;

    public NumberValueResolver(IRepository repository)
    {
        _repository = repository;
    }

    public int Resolve(NumberModel source, NumberDto destination, int destMember, ResolutionContext context)
    {
        return _repository.GetNumber().Number + 3;
    }
}

public class AnotherNumberValueResolver : IValueResolver<NumberModel, NumberDto, string>
{
    public int Resolve(NumberModel source, NumberDto destination, string destMember, ResolutionContext context)
    {
        return $"{source.Number} number(s)";
    }
}

然后我想我会在测试中这样做

var repositoryMock = new Mock<IRepository>();
repositoryMock.Setup(s => s.GetNumber()).Returns(new NumberModel { Number = 3 });

var mapper = new MapperConfiguration(mc =>
{
    mc.AddProfile<NumberProfile>();
    mc.ConstructServicesUsing(s => new NumberValueResolver(repositoryMock.Object));
    mc.ConstructServicesUsing(s => new AnotherNumberValueResolver());
});

var service = new Service(repositoryMock.Object, mapper.CreateMapper());

但后来我收到错误：

System.InvalidCastException：无法将“AutoMapper_app.ValueResolvers.AnotherNumberValueResolver”类型的对象强制转换为“AutoMapper_app.ValueResolvers.NumberValueResolver”类型。

我是否误解了ConstructServicesUsingValueResolvers 的用法，或者它是完全不同的东西？我错过了一些非常明显的东西吗？这可能是糟糕的设计吗？

Answer 1

有同样的问题。在研究了预期的结果之后，函数委托会根据（预期解析器的）类型返回解析器。所以像

x.ConstructServicesUsing(t =>
{
  if (t.Name.Contains("SomeObjectTypeResolver"))
    return new SomeObjectTypeResolver();
  // add more if statements if you have more than 2 resolvers
  return new SomeOtherObjectTypeResolver();
});