AutoMapper从两个源映射表达式引发异常问题求助

刚好我之前处理过类似的场景，结合你用的Asp.Net Core 2.0和AutoMapper 6.2.2，给你整理完整的配置和实现步骤：

首先先补全你的模型类（添加了属性类型，方便实际测试）：

public class UserA 
{ 
    public int CustomerId { get; set; } 
    public string CustomerName { get; set; } 
} 

public class UserB 
{ 
    public int CustomerId { get; set; } 
    public string CustomerEmail { get; set; } 
} 

public class UserViewModel
{ 
    public int Id { get; set; } 
    public string CustomerName { get; set; } 
    public string CustomerEmail { get; set; } 
}

一、正向映射：从UserA+UserB到UserViewModel #

AutoMapper 6.x支持直接从多个源对象映射到单个目标对象，你只需要在Profile配置里明确每个目标成员的来源：

public class MappingProfile : Profile
{
    public MappingProfile()
    {
        // 配置双源映射到UserViewModel
        CreateMap<object[], UserViewModel>()
            .ForMember(dest => dest.Id, opt => opt.MapFrom(src => ((UserA)src[0]).CustomerId))
            // 这里要确保两个源的CustomerId一致，或者根据业务需求选择其中一个
            .ForMember(dest => dest.CustomerName, opt => opt.MapFrom(src => ((UserA)src[0]).CustomerName))
            .ForMember(dest => dest.CustomerEmail, opt => opt.MapFrom(src => ((UserB)src[1]).CustomerEmail));

        // 另一种灵活方案：分开配置单源到目标的映射，再手动合并
        // CreateMap<UserA, UserViewModel>()
        //     .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src.CustomerId));
        // CreateMap<UserB, UserViewModel>();
    }
}

使用的时候，直接传入两个源对象的数组即可：

var userA = new UserA { CustomerId = 1, CustomerName = "John Doe" };
var userB = new UserB { CustomerId = 1, CustomerEmail = "john@example.com" };

var viewModel = _mapper.Map<UserViewModel>(new object[] { userA, userB });

如果用分开配置单源的方式，需要手动合并属性：

var viewModel = _mapper.Map<UserViewModel>(userA);
_mapper.Map(userB, viewModel);

二、反向映射：从UserViewModel到UserA/UserB #

反向映射需要分别创建从ViewModel到两个源模型的映射配置，把ViewModel的属性拆分到不同类中：

public class MappingProfile : Profile
{
    public MappingProfile()
    {
        // 正向映射（同上）
        CreateMap<object[], UserViewModel>()
            .ForMember(dest => dest.Id, opt => opt.MapFrom(src => ((UserA)src[0]).CustomerId))
            .ForMember(dest => dest.CustomerName, opt => opt.MapFrom(src => ((UserA)src[0]).CustomerName))
            .ForMember(dest => dest.CustomerEmail, opt => opt.MapFrom(src => ((UserB)src[1]).CustomerEmail));

        // 反向映射到UserA
        CreateMap<UserViewModel, UserA>()
            .ForMember(dest => dest.CustomerId, opt => opt.MapFrom(src => src.Id))
            .ForMember(dest => dest.CustomerName, opt => opt.MapFrom(src => src.CustomerName));

        // 反向映射到UserB
        CreateMap<UserViewModel, UserB>()
            .ForMember(dest => dest.CustomerId, opt => opt.MapFrom(src => src.Id))
            .ForMember(dest => dest.CustomerEmail, opt => opt.MapFrom(src => src.CustomerEmail));
    }
}

使用反向映射的代码示例：

var viewModel = new UserViewModel { Id = 1, CustomerName = "John Doe", CustomerEmail = "john@example.com" };

var userA = _mapper.Map<UserA>(viewModel);
var userB = _mapper.Map<UserB>(viewModel);

三、Asp.Net Core 2.0中注入AutoMapper #

别忘了在Startup.cs里配置AutoMapper服务：

public void ConfigureServices(IServiceCollection services)
{
    // 注册AutoMapper，扫描程序集里的Profile类
    services.AddAutoMapper(typeof(MappingProfile));
    
    // 其他服务配置...
}

这样就能完美实现你需要的双源映射和反向映射功能了，要是有特殊业务逻辑，还可以在MapFrom里加入自定义转换逻辑哦。

内容的提问来源于stack exchange，提问作者Konrad