Automapper 表达式映射问题答案

【问题标题】：Automapper Expression Mapping IssueAutomapper 表达式映射问题
【发布时间】：2018-12-27 05:41:59
【问题描述】：

使用AutoMapper.Extensions.Expression 的表达式映射不映射表达式。

这是我的模型：

public class UserDto
{
    public int Id { get; set; }
    public User User { get; set; }
    //other info
}

public class User
{
    public string Email { get; set; }
    //other info
}


public class UserEntity
{
    public int Id { get; set; }
    public string Email { get; set; }
    //other info
}

我的映射器：

public static class MapperConfiguration
{
    public static void Configure()
    {
        Mapper.Initialize(cfg =>
        {
            cfg.AddProfile(new UserDtoProfile());
        });
    }
}

internal class UserDtoProfile : Profile
{
    public UserDtoProfile()
    {
        CreateMap<UserDto, UserEntity>()
            .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src.Id))
            .ForMember(dest => dest.Email, opt => opt.MapFrom(src => src.User.Email));

        CreateMap<UserEntity, UserDto>()
            .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src.Id))
            .ForMember(dest => dest.User, opt => opt.MapFrom(src => Mapper.Map<UserEntity>(src)));

        CreateMap<UserEntity, User>()
           .ForMember(dest => dest.Email, opt => opt.MapFrom(src => src.Email)).ReverseMap();
    }
}

添加一个 sn-p 以重现该问题：

static void Main(string[] args)
{
    MapperConfiguration.Configure();
    var email = "test@test.com";
    Expression<Func<UserDto, bool>> filterExpression = x => x.User.Email == email;
    var expression = Mapper.Map<Expression<Func<UserEntity, bool>>>(filterExpression);
    Console.WriteLine("Old Expression : " + filterExpression.Body);
    Console.WriteLine("New Expression : " + expression.Body);
    Console.Read();
}

这个输出是：

旧表达式：(x.User.Email == "asd")
新表达式：(x.User.Email == "asd")

但是，我希望它能够输出：

旧表达式：(x.User.Email == "asd")
新表达式：(x.Email == "asd")

没有按我预期工作的特定行是：

Expression<Func<UserDto, bool>> filterExpression = x => x.User.Email == email;
var expression = Mapper.Map<Expression<Func<UserEntity, bool>>>(filterExpression);

我正在使用AutoMapper v8.0.0 和AutoMapper.Extensions.Expression v2.0.0

【问题讨论】：

标签： c# lambda automapper automapper-8

【解决方案1】：

您忘记配置表达式映射。您的设置应该是：

Mapper.Initialize(cfg =>
{
    cfg.AddExpressionMapping();
    cfg.AddProfile(new UserDtoProfile());
});

我并没有真正使用过 AutoMapper，也从未使用过表达式映射，但根据 this github issue，映射似乎是表达式的反向映射。您当前的映射将不起作用，并且在执行时会崩溃。您需要将映射更改为：

internal class UserDtoProfile : Profile
{
    public UserDtoProfile()
    {
        CreateMap<UserDto, UserEntity>()
            .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src.Id))
            .ForMember(dest => dest.Email, opt => opt.MapFrom(src => src.User.Email))
            .ReverseMap();

        CreateMap<UserEntity, User>()
           .ForMember(dest => dest.Email, opt => opt.MapFrom(src => src.Email)).ReverseMap();
    }
}

运行它会给出输出：

旧表达式：(x.User.Email == "asd")
新表达式：(x.Email == "asd")

【讨论】：