用于查找属性的 Lambda 表达式

Question

我想从promotionCatalogResponseRootObject 检索LineOfBusiness 属性，其中PromotionID 等于myId

public class PromotionCatalogResponseRootObject
{
   public PromotionCatalogResponse PromotionCatalog { get; set; }
}

public class Promotion
{
  public string PromotionId { get; set; }
  public string LineOfBusiness { get; set; }
  public string PromotionName { get; set; }
}

public class PromotionCatalogResponse
{
  public List<Promotion> Promotion { get; set; }
}

我一开始就是这样，但我知道我做错了。请指导

string myId = "7596";
string lineOfBusiness = dataPromotionCatalog.PromotionCatalog
                                            .Promotion.Find(p => p.LineOfBusiness);

Answer 1

您缺少的是Find 方法期望接收具有bool 返回值的谓词，但您返回的是string，LineOfBusiness 属性。

首先过滤您想要的项目，然后选择所需的属性。此外，我会选择Where 而不是Find。 (Find() vs. Where().FirstOrDefault())

var result = dataPromotionCatalog.PromotionCatalog.Promotion
                                 .Where(i => i.PromotionId == myId)
                                 .Select(i => i.LineOfBusiness);

或在查询语法中

var result = (from item in dataPromotionCatalog.PromotionCatalog.Promotion
              where item.PromotionId == myId
              select item.LineOfBusiness);

如果您期待/想要拥有一件商品，请使用FirstOrDefault：

var result = dataPromotionCatalog.PromotionCatalog.Promotion
                 .FirstOrDefault(i => i.PromotionId == myId)?.LineOfBusiness;