C# - 在 Linq Where Any 语句中使用的要列出的字符串

Question

我想使用这个字符串作为过滤器来删除 linq 查询中的一些 Id

public class ProductKitMakerDto
{
    public int Id { get; set; }
    public string TitleShort { get; set; }
    public string Media { get; set; }
}

[HttpPost]
public ActionResult KitItemSelect(string culture)
{
    string productMakerIds = "4174,2196,2201,2460,2508,2204";

    //create a list
    var productMakerList = new List<ProductKitMakerDto>();
    foreach (int i in productMakerIds)
    {
        productMakerList.Add(new ProductKitMakerDto { Id = i });
    }

    var itemselects = (from p in _context.Products
                   where p.Matrix == 2400
                   select new ProductKitMakerDto()
                   {
                   Id = p.Id,
                   TitleShort = culture == "de" ? p.TitleShortDe :
                                culture == "fr" ? p.TitleShortFr :
                                p.TitleShortEn,
                    Media = "/img/" + p.Photo,
                    }).ToList();

    //From this query I get 40 results.
    //Then I want to remove the ones from the list:

    //itemselects = itemselects.Where(i => !productMakerList.Any(pml =>pml.Id == i.Id));

    //1st (above) I get an Error CS0266 asking for explicit cast. So aplly the modification

    itemselects = (List<ProductKitMakerDto>)itemselects.Where(i => !productMakerList.Any(pml =>pml.Id == i.Id));

    return Json(itemselects, JsonRequestBehavior.AllowGet);
}

我得到 500（内部服务器错误） - xhr.send( options.hasContent && options.data || null ); 我猜这个列表是空的。 任何想法？谢谢

Answer 1

foreach (string i in productMakerIds.Split(','))
    {
        productMakerList.Add(new ProductKitMakerDto { Id = int.Parse(i) });
    }

Answer 2

1. 这不起作用

   string productMakerIds = "4174,2196,2201,2460,2508,2204";
   var productMakerList = new List<ProductKitMakerDto>();
   foreach (int i in productMakerIds)
   {
       productMakerList.Add(new ProductKitMakerDto { Id = i });
   }
   

因为您需要先以逗号分隔并将string 解析为int：

   foreach (string i in productMakerIds.Split(',')) // and parse i to int with int.Parse

1. 但由于它是字符串文字，因此首先要正确初始化它。不要使用List<ProductKitMakerDto>，因为你只需要List<int>，那么你可以使用Contains：

   var productMakerList = new List<int>
   {
       4174, 2196, 2201, 2460, 2508 , 2204
   };
   

2. 如果它不是一个列表并且Enumerable.Where 不返回一个列表，则不能转换为列表：

   itemselects = (List<ProductKitMakerDto>)itemselects.Where(i => !productMakerList.Any(pml =>pml.Id == i.Id));
   

您需要在Where 之后附加ToList

   itemselects = itemselects
       .Where(i => !productMakerList.Any(pml =>pml.Id == i.Id))
       .ToList();

但如前所述，您也可以在第一次创建该列表之前使用此 Where，因此应包含应支持的 Contains 条件：

var itemselects = (from p in _context.Products
                   where p.Matrix == 2400
                   && !productMakerList.Contains(p.Id)
                   select new ProductKitMakerDto()
                   {
                      Id = p.Id,
                      TitleShort = culture == "de" 
                         ? p.TitleShortDe 
                         : culture == "fr" ? p.TitleShortFr : p.TitleShortEn,
                      Media = "/img/" + p.Photo,
                   }).ToList();