如何为两种不同场景配置AutoMapper单一映射规则？

从API获取行程数据后，需通过AutoMapper将API模型TripModel映射至EF Core实体Trip并存储到SQL Server数据库。大部分映射逻辑简单直接，但存在以下特殊场景需要处理：

• 当TripModel.ReasonForTravel（int?类型）有值且大于0时，需通过自定义TravelReasonConverter将其转换为目标字符串；
• 当TripModel.ReasonForTravel无值或小于等于0时，直接取用TripModel.CustomTravelReason的属性值。

如何在AutoMapper的CreateMap配置中实现该逻辑，完成一步映射？以下是现有代码：

public class TripModel
{
    public string Firstname { get; set; }
    public string Lastname { get; set; }
    public int? ReasonForTravel { get; set; }
    public string CustomTravelReason { get; set; }
    // 其他无关属性
}

public class Trip
{
    public string Firstname { get; set; }
    public string Lastname { get; set; }
    public string ReasonForTrip { get; set; }
}

public class TripProfile : Profile
{
    public TripProfile()
    {
        CreateMap<TripModel, Trip>()
            // 示例基础映射（实际可省略）
            .ForMember(dest => dest.Firstname, opt => opt.MapFrom(src => src.Firstname))
            .ForMember(dest => dest.Lastname, opt => opt.MapFrom(src => src.Lastname))
            
            // 疑问：如何同时处理两种场景？
            //.ForMember(dest => dest.ReasonForTrip, opt => opt.ConvertUsing(new TravelReasonConverter(), src => src.ReasonForTravel))
            //.ForMember(dest => dest.ReasonForTrip, opt => opt.MapFrom(src => src.CustomTravelReason));
    }
}

方法一：直接在MapFrom中编写条件逻辑 #

无需额外创建转换器，直接在MapFrom的委托中完成条件判断与转换：

public class TripProfile : Profile
{
    public TripProfile()
    {
        CreateMap<TripModel, Trip>()
            .ForMember(dest => dest.Firstname, opt => opt.MapFrom(src => src.Firstname))
            .ForMember(dest => dest.Lastname, opt => opt.MapFrom(src => src.Lastname))
            .ForMember(dest => dest.ReasonForTrip, opt => opt.MapFrom(src => 
                // 判断条件：ReasonForTravel有值且大于0
                src.ReasonForTravel.HasValue && src.ReasonForTravel.Value > 0 
                    // 满足条件时调用自定义转换器
                    ? new TravelReasonConverter().Convert(src.ReasonForTravel.Value, null, null) 
                    // 不满足时使用自定义原因
                    : src.CustomTravelReason));
    }
}

方法二：封装自定义转换器处理完整逻辑 #

如果逻辑较复杂或需要复用，可创建一个接收TripModel的自定义转换器，封装所有判断与转换逻辑：

// 自定义转换器：接收TripModel，返回对应的行程原因字符串
public class TripReasonConverter : IValueConverter<TripModel, string>
{
    public string Convert(TripModel source, ResolutionContext context)
    {
        if (source.ReasonForTravel.HasValue && source.ReasonForTravel.Value > 0)
        {
            // 调用原有的TravelReasonConverter处理整数转字符串
            var intConverter = new TravelReasonConverter();
            return intConverter.Convert(source.ReasonForTravel.Value, null, null);
        }
        // 返回自定义原因
        return source.CustomTravelReason;
    }
}

// 在Profile中配置使用该转换器
public class TripProfile : Profile
{
    public TripProfile()
    {
        CreateMap<TripModel, Trip>()
            .ForMember(dest => dest.Firstname, opt => opt.MapFrom(src => src.Firstname))
            .ForMember(dest => dest.Lastname, opt => opt.MapFrom(src => src.Lastname))
            .ForMember(dest => dest.ReasonForTrip, opt => opt.ConvertUsing<TripReasonConverter>());
    }
}

内容的提问来源于stack exchange，提问作者marc_s