如何使用AutoMapper映射集合对象 替换foreach循环设置OwnerData的逻辑

步骤1：配置AutoMapper映射规则 #

自定义映射Profile类，配置同类型映射规则，支持外部传入Owner实例为Car的OwnerData属性赋值：

using AutoMapper;

public class CarProfile : Profile
{
    public CarProfile()
    {
        // 配置Owner到Owner的映射，忽略不需要赋值的Id字段
        CreateMap<Owner, Owner>()
            .ForMember(dest => dest.Id, opt => opt.Ignore());

        // 配置Car到Car的映射，保留原Car的Id、Name属性不覆盖
        CreateMap<Car, Car>()
            .ForMember(dest => dest.Id, opt => opt.Ignore())
            .ForMember(dest => dest.Name, opt => opt.Ignore())
            // 从映射参数中获取外部传入的Owner实例，赋值给OwnerData
            .ForMember(dest => dest.OwnerData, opt => opt.MapFrom((src, dest, destMember, context) =>
            {
                var owner = (Owner)context.Items["OwnerInfo"];
                return context.Mapper.Map<Owner>(owner);
            }));
    }
}

步骤2：初始化AutoMapper #

ASP.NET Core 依赖注入环境 #

在Program.cs中注册AutoMapper服务：

builder.Services.AddAutoMapper(typeof(CarProfile));

之后在业务类中通过构造函数注入IMapper接口即可使用。

非依赖注入环境 #

手动构造Mapper实例：

var config = new MapperConfiguration(cfg => cfg.AddProfile<CarProfile>());
var mapper = config.CreateMapper();

步骤3：替换原有foreach逻辑 #

直接调用AutoMapper的集合映射方法，传入查询到的cars集合和ownerData参数，自动完成批量赋值：

Owner ownerData = repository.Get<Owner>(id);
IEnumerable<Car> cars = repository.Get<Car>();

// 批量映射替换整段foreach逻辑
var data = _mapper.Map<IEnumerable<Car>>(cars, opt =>
{
    opt.Items["OwnerInfo"] = ownerData;
});

如果你不需要自动适配Owner新增字段，也可以直接在映射规则里硬编码赋值三个字段，效果和原foreach完全一致：

CreateMap<Car, Car>()
    .ForMember(dest => dest.Id, opt => opt.Ignore())
    .ForMember(dest => dest.Name, opt => opt.Ignore())
    .ForMember(dest => dest.OwnerData, opt => opt.MapFrom((src, dest, destMember, context) =>
    {
        var owner = (Owner)context.Items["OwnerInfo"];
        return new Owner
        {
            CarName = owner.CarName,
            Name = owner.Name,
            Phone = owner.Phone
        };
    }));

内容的提问来源于stack exchange，提问作者user1765862