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Question

比方說，我們有映射兩個源類型，和一個目的：

class TSource 
{ 
    public float A { get; set; } 
    public float B { get; set; } 
} 

class TSupport 
{ 
    public float C { get; set; } 
    public float D { get; set; } 
} 

class TDestination 
{ 
    public float A { get; set; } 
    public float B { get; set; } 
    public float C { get; set; } 
    public float D { get; set; } 
} 

，並與一些方法獲得TSupport的情況下，使用TSource例如：

Mapper.CreateMap<TSource, TDestination>(); 
Mapper.CreateMap<TSupport, TDestination>(); 
//... 
var support = GetSupportInstance(source); 

var destination = Mapper.Map<TSource, TDestination>(source); 
Mapper.Map(support, destination); 

這也可以在單來完成：

private TSupport GetSupportInstance(TSource source) 

所以，通常情況下，我會用雙重映射做到這一點使用手動決心映射：

Mapper.CreateMap<TSource, TDestination>() 
    .ForMember(desc => desc.C, opt => opt.ResolveUsing(src => 
    { 
     var support = GetSupportInstance(src); 
     return support.C; 
    })) 
    .ForMember(desc => desc.D, opt => opt.ResolveUsing(src => 
    { 
     var support = GetSupportInstance(src); 
     return support.D; 
    })); 

正如你所看到的，我使用的是GetSupportInstance兩次，爲每個屬性。所以，最後，我的問題是 - 是否有可能獲得一次映射的支持，以某種方式存儲它，並在不同屬性的映射中重用它？

Answer 1

如何：

Mapper.CreateMap<TSource, TDestination>() 
    .ForMember(d => d.C, x => x.Ignore()) 
    .ForMember(d => d.D, x => x.Ignore()) 
    .AfterMap((src, dst) => { 
     var support = GetSupportInstance(src); 
     dst.C = support.C; 
     dst.D = support.D; 
    }); 

Answer 2

我可能會去使用緩存你需要的情況下自定義解析。它看起來像這樣。

public class MySupportInstanceResolver : ValueResolver<TSource, TDestination> 
{ 
    private static readonly ISupportInstance _supportInstance; 

    [ImportingConstructor] 
    public MySupportInstanceResolver() 
    { 
     _supportInstance=GetSupportInstance(); 
    } 

    protected override string ResolveCore(Journal source) 
    { 
     return _supportInstance; 
    } 
} 

然後，你可以使用它作爲：

cfg.CreateMap<TSource, Tdest>() 
     .ForMember(dest => dest.C, 
      opt => opt.ResolveUsing<MySupportInstanceResolver>().FromMember(name => name.C)); 
});