如何使用AutoMapper将Customer与Person合并映射为CustomerModel？

现有以下C#类定义：

Customer类 #

public class Customer
{
    public int Id { get; set; }
    public int PersonId { get; set; }
    public int DiscountValue { get; set; }
    public Person Person { get; set; }
    public ICollection<Receipt> Receipts { get; set; }
}

Person类 #

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Surname { get; set; }
    public DateTime BirthDate { get; set; }
}

CustomerModel类 #

public class CustomerModel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Surname { get; set; }
    public DateTime BirthDate { get; set; }
    public int DiscountValue { get; set; }
    public ICollection<int> ReceiptsIds { get; set; }
}

需要将Customer和Person合并映射为CustomerModel，当前的AutoMapper配置尝试使用元组但未完善映射规则，以下是两种场景下的正确实现：

场景1：Customer已关联Person导航属性 #

如果你的Customer对象已通过EF Core等方式加载了Person导航属性（即customer.Person不为null），可直接基于Customer配置映射，无需传入元组：

public class AutomapperProfile : Profile
{
    public AutomapperProfile()
    {
        CreateMap<Customer, CustomerModel>()
            // 自动匹配的属性可省略显式配置，这里写出是为了清晰
            .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src.Id))
            .ForMember(dest => dest.DiscountValue, opt => opt.MapFrom(src => src.DiscountValue))
            // 映射Person导航属性的字段
            .ForMember(dest => dest.Name, opt => opt.MapFrom(src => src.Person.Name))
            .ForMember(dest => dest.Surname, opt => opt.MapFrom(src => src.Person.Surname))
            .ForMember(dest => dest.BirthDate, opt => opt.MapFrom(src => src.Person.BirthDate))
            // 将Receipts集合转换为Id集合，处理空集合避免异常
            .ForMember(dest => dest.ReceiptsIds, opt => opt.MapFrom(src => src.Receipts?.Select(r => r.Id) ?? new List<int>()));
    }
}

使用方式：

var customerModel = mapper.Map<CustomerModel>(customer);

场景2：需传入独立的Customer和Person实例（元组方式） #

如果必须通过元组传递两个独立的实例，需明确指定每个属性的来源是元组的第一个或第二个元素：

public class AutomapperProfile : Profile
{
    public AutomapperProfile()
    {
        CreateMap<(Customer Customer, Person Person), CustomerModel>()
            // 从Customer实例取属性
            .ForMember(dest => dest.Id, opt => opt.MapFrom(src => src.Customer.Id))
            .ForMember(dest => dest.DiscountValue, opt => opt.MapFrom(src => src.Customer.DiscountValue))
            .ForMember(dest => dest.ReceiptsIds, opt => opt.MapFrom(src => src.Customer.Receipts?.Select(r => r.Id) ?? new List<int>()))
            // 从Person实例取属性
            .ForMember(dest => dest.Name, opt => opt.MapFrom(src => src.Person.Name))
            .ForMember(dest => dest.Surname, opt => opt.MapFrom(src => src.Person.Surname))
            .ForMember(dest => dest.BirthDate, opt => opt.MapFrom(src => src.Person.BirthDate));
    }
}

使用方式：

var customerModel = mapper.Map<CustomerModel>((customer, person));

注意事项 #

• 处理Receipts空集合时，用?.Select()和空合并运算符避免空引用异常
• 属性名称完全匹配时，AutoMapper会自动映射，可省略对应.ForMember配置，显式写出是为了提升代码可读性

内容的提问来源于stack exchange，提问作者Fatality99