AutoMapper.ProjectTo與字段級別類型轉換

Question

我想使用AutoMapper的ProjectTo擴展方法將基於實體框架表的對象轉換爲自定義的DTO。在EF對面的人實體看起來是這樣的：

public partial class Person 
{ 
    public int PersonId { get; set; } 
    public string Name { get; set; } 
    public string Age { get; set; } 
} 

的PersonViewModel，我投射到看起來像這樣DTO：

public class PersonViewModel 
{ 
    public PersonViewModel(Person p) 
    { 
     PersonId = p.PersonId; 
     Name = p.Name; 
     Age = Convert.ToInt32(p.Age); 
    } 

    public PersonViewModel() 
    { 

    } 

    public PersonViewModel(int id, string name, int age) 
    { 
     PersonId = id; 
     Name = name; 
     Age = age; 
    } 

    public int PersonId { get; set; } 
    public string Name { get; set; } 
    public int Age { get; set; } 
} 

要注意的關鍵一點是，人表中包含的字段稱爲Age的nvarchar類型，PersonViewModel具有Age類型的int類型。不幸的是，我無法更改表格，而必須找到轉換數據的方法。

以下代碼是我嘗試過的AutoMapper配置，它們的「問題」以及使用代碼（數據庫調用等）。

MapperConfiguration config = new MapperConfiguration(cfg => 
     { 
      // ----- Throws "Unable to create map expression" exception ------ 
      //cfg.CreateMap<Person, PersonViewModel>(); 


      // ----- Throws "Linq to Entities does not support method" exception ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ForMember(dest => dest.Age, opt => opt.MapFrom(src => Convert.ToInt32(src.Age))); 


      // ----- Throws "Unable to create map expression" exception ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ConstructProjectionUsing(src => new PersonViewModel 
      // { 
      //  PersonId = src.PersonId, 
      //  Name = src.Name, 
      //  Age = Convert.ToInt32(src.Age) 
      // }); 


      // ----- Throws "Unable to create map expression" exception ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ConstructProjectionUsing(src => new PersonViewModel(src.PersonId, src.Name, Convert.ToInt32(src.Age))); 


      // ----- Throws "Unable to create map expression" exception ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ConstructProjectionUsing(src => new PersonViewModel(src.PersonId, src.Name, 25)); 


      // ----- Throws "Linq to Entities does not support method" exception ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ProjectUsing(src => new PersonViewModel 
      // { 
      //  PersonId = src.PersonId, 
      //  Name = src.Name, 
      //  Age = Convert.ToInt32(src.Age) 
      // }); 


      // ----- Throws "Unable to create map expression" exception ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ConstructUsing(src => new PersonViewModel 
      // { 
      //  PersonId = src.PersonId, 
      //  Name = src.Name, 
      //  Age = Convert.ToInt32(src.Age) 
      // }); 


      // ----- Throws "Unable to create map expression" exception ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ConstructUsing(src => new PersonViewModel(src)); 


      // ----- Doesn't throw exception, but all values are null or 0. ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ConvertUsing(src => new PersonViewModel 
      // { 
      //  PersonId = src.PersonId, 
      //  Name = src.Name, 
      //  Age = Convert.ToInt32(src.Age) 
      // }); 


      // ----- Doesn't throw exception, but all values are null or 0. ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ConvertUsing(src => new PersonViewModel(src.PersonId, src.Name, Convert.ToInt32(src.Age))); 


      // ----- Works, but bypasses the conversion I need ------ 
      //cfg.CreateMap<Person, PersonViewModel>() 
      // .ProjectUsing(src => new PersonViewModel 
      // { 
      //  PersonId = src.PersonId, 
      //  Name = src.Name, 
      //  Age = 25 
      // }); 


      // ----- Works, but bypasses the conversion I need ------ 
      cfg.CreateMap<Person, PersonViewModel>() 
       .ForMember(dest => dest.Age, opt => opt.MapFrom(src => 35)); 
     }); 

     using (FamilyEntities db = new FamilyEntities()) 
     { 
      PersonViewModel p = db.Set<Person>() 
       .Where(x => x.PersonId == 1) 
       .ProjectTo<PersonViewModel>(config) 
       .SingleOrDefault(); 

      Console.WriteLine("Name: " + p.Name + Environment.NewLine + "Age: " + p.Age); 
     } 

     Console.ReadLine(); 

是否可以使用AutoMapper的ProjectTo將字符串轉換爲int？其次，如果可能的話，那個配置是​​什麼樣的？

在此先感謝您的幫助。

Answer 1

https://stackoverflow.com/a/24027242/1736944介紹瞭如何將功能添加到EF。基本上生成的查詢將不得不執行類型轉換。

Answer 2

你的第一個嘗試是爲什麼這不起作用。實體框架不知道如何將一個字符串轉換爲一個整型，所以你被弄糊塗了。其他方面都不重要，重要的是EF給你的例外。

如果EF無法支持轉換，AutoMapper無法爲您提供幫助。

相反，我會做類似轉換您的視圖模型的內部：

public class PersonViewModel 
{ 
    public int PersonId { get; set; } 
    public string Name { get; set; } 
    public string Age { get; set; } 
    public int AgeValue => Convert.ToInt32(Age); 
}