c# - AutoMapper 展平嵌套集合

Question

我试图弄清楚如何将商家集合扁平化，每个商家都包含一个订单集合到一个扁平的 OrderViewModel 列表。

这是我的 DTO:

public class Merchant
{
    public string MerchantName { get; set; }
    public List<Order> Orders { get; set; }
}

public class Order
{
    public string OrderId { get; set; }
}

这是 View 模型:

public class OrderViewModel
{
    public string MerchantName { get; set; }
    public string OrderId { get; set; }
}

我的目标是将 List 扁平化为 List 而以下测试结构应产生 6 个 View 模型:

var myMerchants = new List<Merchant>
{
    new Merchant
    {
        MerchantName = "Merchant X",
        Orders = new List<Order>
        {
             new Order { OrderId = "Order 1"},
             new Order { OrderId = "Order 2"},
             new Order { OrderId = "Order 3"}
        }
    },
    new Merchant
    {
        MerchantName = "Merchant Y",
        Orders = new List<Order>
        {
            new Order { OrderId = "Order 4"},
            new Order { OrderId = "Order 5"},
            new Order { OrderId = "Order 6"}
        }
    }
 };

 var models = Mapper.Map<List<OrderViewModel>>(myMerchants);

Answer 1

因为根对象的基数不是 1:1，(即 2 个根 Merchants 需要映射到 6 个 OrderViewModels)，您可能需要求助于一个custom TypeConverter并在集合级别进行操作，您可以在其中使用 .SelectMany 进行展平:

public class MyTypeConverter : ITypeConverter<IEnumerable<Merchant>, List<OrderViewModel>>
{
    public List<OrderViewModel> Convert(ResolutionContext context)
    {
        if (context == null || context.IsSourceValueNull)
            return null;

        var source = context.SourceValue as IEnumerable<Merchant>;

        return source
            .SelectMany(s => s.Orders
              .Select(o => new OrderViewModel
              {
                  MerchantName = s.MerchantName,
                  OrderId = o.OrderId
              }))
              .ToList();
    }
}

然后你可以引导:

Mapper.CreateMap<IEnumerable<Merchant>, List<OrderViewModel>>()
    .ConvertUsing<MyTypeConverter>();

然后这样映射:

var models = Mapper.Map<List<OrderViewModel>>(myMerchants);