掌握数据多态性

Question

我提到我与 DTO 的合作不多。我在 DataTransfereObjects 上玩弄多态主义。我想不出一个好的解决方案，所以我制作了这个代码示例来掌握多态与 DataTransfereObjects 和不同的逻辑实现，使用多态、泛型、接口、抽象等。

请检查代码。提示我有什么不好，可以做得更好或更容易。检查accessmodifier，还要检查SOLID（认为我没有正确理解它）。最后好像太复杂了，这样解决是不是很常见？

实际上，我尝试调用一些（反）序列化程序逻辑，它使用 baseDto 来获取派生的 dto，而不会丢失它们的特定信息。该代码应该是解决此类问题的干净抽象沙箱。

void Main()
{
    var twoIngrDto = new TwoIngredientsDto();
    var threeIngrDto = new ThreeIngredientsDto(); 

    var twoIngrMulAnswerChecker = new TwoIngredientsMultiplicationAnswerChecker();
    var threeIngrAddAnswerChecker = new ThreeIngredientsAdditionAnswerChecker();

    twoIngrMulAnswerChecker.IsTheAnswerCheckImplementationTheAnswer(twoIngrDto); //TRUE .Dump();
    threeIngrAddAnswerChecker.IsTheAnswerCheckImplementationTheAnswer(threeIngrDto); //TRUE .Dump();
    twoIngrMulAnswerChecker.IsTheAnswerCheckImplementationTheAnswer(threeIngrDto); //FALSE .Dump();

    IAnswerCheck answerchecker = new IngredientsAnswerChecker();
    answerchecker.CheckAnswer(twoIngrMulAnswerChecker, twoIngrDto); //TRUE .Dump();
    answerchecker.CheckAnswer(threeIngrAddAnswerChecker, threeIngrDto); //TRUE .Dump();

    /// QUESTION: How can I use the answerchecker 'twoIngrMulAnswerChecker' with the derived DTO 'threeIngrDto'
    /// It failes with following error:
    /// The type 'UserQuery.TwoIngredientsMultiplicationAnswerChecker' cannot be used as 
    /// type parameter 'T' in the generic type or method 'UserQuery.IngredientsAnswerChecker.CheckAnswer<T,DTO>(T, DTO)'. 
    /// There is no implicit reference conversion from 'UserQuery.TwoIngredientsMultiplicationAnswerChecker' 
    /// to 'UserQuery.TheAnswerChecker<UserQuery.ThreeIngredientsDto>'.
    //answerchecker.CheckAnswer(twoIngrMulAnswerChecker, threeIngrDto).Dump();
    answerchecker.CheckAnswer(twoIngrMulAnswerChecker, (TwoIngredientsDto)threeIngrDto).Dump(); // is casting the solution? 
}

interface IAnswerCheck
{
    bool CheckAnswer<T, DTO>(T answerCkecker, DTO ingredientsDto) 
        where T : TheAnswerChecker<DTO>
        where DTO : IngredientDto;
}

public abstract class TheAnswerChecker<T> where T : IngredientDto
{
    internal abstract int TheAnswerCheckImplementation(T answerIngredietsDto);
    private int TheAnswer {get { return 42;} }

    public bool IsTheAnswerCheckImplementationTheAnswer(T answerIngredietsDto)
    {
        return TheAnswer == TheAnswerCheckImplementation(answerIngredietsDto);
    }
}

//generate a base class
public class IngredientsAnswerChecker : IAnswerCheck //: TheAnswerChecker<IngredientDto>
{
    public bool CheckAnswer<T, DTO>(T answerCkecker, DTO ingredientsDto) 
        where T : TheAnswerChecker<DTO>
        where DTO : IngredientDto
    {
        return answerCkecker.IsTheAnswerCheckImplementationTheAnswer(ingredientsDto);
    }
}

public class TwoIngredientsMultiplicationAnswerChecker : TheAnswerChecker<TwoIngredientsDto>
{
    internal override int TheAnswerCheckImplementation(TwoIngredientsDto answerIngredietsDto) //where T : TwoIngredientsDto
    { 
        return answerIngredietsDto.A * answerIngredietsDto.B;
    }
}

public class ThreeIngredientsAdditionAnswerChecker : TheAnswerChecker<ThreeIngredientsDto>
{
    internal override int TheAnswerCheckImplementation(ThreeIngredientsDto answerIngredietsDto)
    {
        return answerIngredietsDto.A + answerIngredietsDto.B + answerIngredietsDto.C;
    }
}

public class IngredientDto
{
    public IngredientDto()
    {
        Id = Guid.NewGuid();
    }
    public Guid Id { get; private set; }
}

public class TwoIngredientsDto : IngredientDto
{
    public virtual int A {get {return 6;}}
    public virtual int B {get {return 7;}} 
}

public class ThreeIngredientsDto : TwoIngredientsDto
{
    public override int B {get {return 24;}} 
    public int C {get {return 12;}} 
}

Answer 1

DTO 背后的想法是使用 dummy/plain 对象进行数据传输，因此您应该避免向此类对象增加复杂性，例如通过继承，否则 DTO 将失去其简单和序列化友好的主要目的。

关于您的“演员问题”，答案是肯定的，演员将允许使用 ThreeIngredientsDto 而不是 TwoIngredientsDto。

对于私有属性“TheAnswer”，我建议使用 const。

总体而言，您的示例尊重 SOLID 原则，但请注意，并非总是必须将代码拆分为原子片段以实现单一职责原则。例如，我不使用 TwoIngredientsMultiplicationAnswerChecker、ThreeIngredientsAdditionAnswerChecker 和 TheAnswerChecker 类，而是使用单个类 TheAnswerChecker每种类型的 DTO 都有一个重载方法，这样您的代码将更具可读性和可理解性，毕竟，您的班级责任只是检查答案。当然，如果为每种类型的 DTO 检查答案的逻辑将非常复杂并且需要大量代码，那么拆分为不同的类可能是有意义的。关键是 SOLID 应该代表一组在构建代码时要牢记的原则，但有时违反某些规则会带来很多好处，在这种情况下，您应该做出这种妥协。