Automapper 自定义多对一转换

Question

Automapper 多对一转换

如何将源对象中的许多属性的值转换为目标对象中的单一类型？ 我可以在这种情况下使用Value Resolvers吗？或者也许有更好的解决方案？

文档

这里是 example 来自 documentation - 一对一的转换

Mapper.CreateMap<Source, Destination>()
    .ForMember(dest => dest.Total,
        opt => opt.ResolveUsing<CustomResolver>().FromMember(src => src.SubTotal));
Mapper.CreateMap<OtherSource, OtherDest>()
    .ForMember(dest => dest.OtherTotal,
        opt => opt.ResolveUsing<CustomResolver>().FromMember(src => src.OtherSubTotal));

public class CustomResolver : ValueResolver<decimal, decimal> {
// logic here
}

案例

我想将两个对象合二为一（多对一转换）。例如：

public class Document
{
    public int CurrencyId {get; set;}
    public int ExchangeRateId {get; set;}
}

public class DocumentDto
{
    public Currency Currency {get; set;}
}

public class CurrencyDetails
{
    public Currency Currency {get; private set;}
    public ExchangeRate ExchangeRate {get; private set;}

    public CurrencyDetails(Currency currency, ExchangeRate exchangeRate)
    {
        Currency = currency;
        ExchangeRate = exchangeRate;
    }
}

我想实现这样的目标：

public class CurrencyResolver : ValueResolver<int, int, CurrencyDetails>
{
    protected override Currency ResolveCore(int currencyId, int exchangeRateId)
    {
        var currency = new Currency(currencyId); //simplified logic
        var exchangeRate = new ExchangeRate(exchangeRateId);

        var currencyDetails = new CurrencyDetails(currency, exchangeRate);
        return currencyDetails;
    }
}

我知道我可以将整个对象作为源对象传递，但对我来说这不是解决方案：

ValueResolver<Document, Currency>

我不能使用完整对象，因为我有很多文档类型，我不想为每个文档创建新的解析器。 在我的情况下，也不允许忽略元素（用于手动转换）。货币转换逻辑必须由 AutoMapper 执行。

转换发生在后台（在主体转换期间）对我来说很重要。

例如：

Document document;
var documentDto = Mapper.Map<DocumentDto>(document); // and in this moment i have proper CurrencyDetails object!

感谢您的建议。

我的解决方案

我想出了两个解决方案，但我不喜欢它们（太脏了）

解决方案 1 - 用接口包装一个类：

public interface ICurrencyHolder
{
    int CurrencyId {get; set;}
    int ExchangeRateId {get; set;}
}

public class Document : ICurrencyHolder
{
    public int CurrencyId {get; set;}
    public int ExchangeRateId {get; set;}
}

并使用带有以下参数的解析器：

ValueResolver<ICurrencyHolder, Currency>

解决方案 2 - 作为源元素对象类型并通过反射获取值

ValueResolver<object, Currency>

这太可怕了！

Answer 1

如果我理解正确，您需要进行以下映射：从 (CurrencyId, ExchangeRateId) 到 Currency。您可以使用Tuple 来实现它（it is a standard .Net class 在这些情况下非常方便）：

Mapper.CreateMap<Tuple<int,int>, Currency>()
   .ForMember(x => x.Currency, cfg => cfg.MapFrom(y => new Currency(y.Item1, y.Item2));

按如下方式调用映射器：

Mapper.Map<Tuple<int,int>, Currency>(Tuple.Create(doc.CurrencyId, doc.ExchangeRateId));

Answer 2

也许你可以这样映射它：

Mapper.CreateMap<Source, Destination>()
      .ConstructUsing(s => Mapper.Map<Source, Currency>(s));

Mapper.CreateMap<Source, Currency>()
      .ForMember(dst => dst.CurrencySymbol, map => map.MapFrom(src => src.DocumentDto.CurrencySymbol))
      .ForMember(dst => dst.ExchangeRate , map => map.MapFrom(src => src.Document.ExchangeRate ));

也可以：

Mapper.CreateMap<Source, Destination>()
      .ConstructUsing(s => Mapper.Map<Source, Currency>(s));

Mapper.CreateMap<Source, Currency>()
      .ConstructUsing(s => Mapper.Map<DocumentDto, Currency>(s))
      .ConstructUsing(s => Mapper.Map<Document, Currency>(s));

Mapper.CreateMap<DocumentDto, Currency>();
Mapper.CreateMap<Document, Currency>();

Answer 3

如果您确定要为每种文档类型执行此操作：

Document document;
var documentDto = Mapper.Map<DocumentDto>(document);

然后您必须为它们中的每一个定义映射。所以我肯定会采用 ICurrencyHolder 的想法并使用这样的解析器：

解析器

public class CurrencyResolver : ValueResolver<ICurrencyHolder, Currency>
{
    protected override Currency ResolveCore(ICurrencyHolder source)
    {
        return new Currency(source.CurrencyId, source.ExchangeRateId);
    }
}

文档“类型”

public class Document : ICurrencyHolder
{
    public int CurrencyId { get; set; }
    public int ExchangeRateId { get; set; }
}

public class ExtendedDocument : ICurrencyHolder
{
    public DateTime SomeDate { get; set; }
    public int CurrencyId { get; set; }
    public int ExchangeRateId { get; set; }
}

public interface ICurrencyHolder
{
    int CurrencyId { get; set; }
    int ExchangeRateId { get; set; }
}

还有映射：

Mapper.CreateMap<Document, DocumentDto>().ForMember(m => m.Currency, opt => opt.ResolveUsing<CurrencyResolver>());
Mapper.CreateMap<ExtendedDocument, DocumentDto>().ForMember(m => m.Currency, opt => opt.ResolveUsing<CurrencyResolver>());

有了它，您可以像这样创建您的 dto，并在映射阶段为您自己解析货币：

var dto = Mapper.Map<DocumentDto>(document);
var extendedDto = Mapper.Map<DocumentDto>(extendedDocument);