LINQ自定義對象列表<Object>成員

Question

CHV1 CDD1            CHV2 CDD2            CHV3 CDD3            CHV4  CDD4                               SortCol                              SearchColCount 
---- -------------------------------------------------- ---- -------------------------------------------------- ---- -------------------------------------------------- ----------- ------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------ -------------- 

Adventure Cafe Columbus         Back Of The House          Cook            624   Adams, Donald, 4180259, A                          A, Adams, Donald, 4180259                          0 
Adventure Cafe Columbus         Back Of The House          Cook            643   Conard, Virgil, 4180469, A                          A, Conard, Virgil, 4180469                          0 
Adventure Cafe Columbus         Back Of The House          Cook            629   Pheiffer, Seth, 4180373, A                          A, Pheiffer, Seth, 4180373                          0 
Adventure Cafe Columbus         Back Of The House          Cook            645   Sees, Patrick, 4180474, A                          A, Sees, Patrick, 4180474                          0 
Adventure Cafe Columbus         Back Of The House          Cook            657   Walter, Derek, 4180508, A                          A, Walter, Derek, 4180508                          0 

以上是來自DB的數據集。

我想使用LINQ獲取數據集並基於上述數據結構創建自定義對象類型，但該對象的成員之一是List數據類型。

我最初發現下面的文章，但它不工作準確，因爲它是一個簡單的字符串列表對象類型： Convert Datatable to Object with Linq and Group by 這是給我下面的錯誤：

Cannot implicitly convert type 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.List'. An explicit conversion exists (are you missing a cast?)

我列出我對上述引用的文章中的代碼進行了修改。理想情況下，我希望能夠基於CDD2，CDD3，CDD4等動態地創建多個「folderItem」列表...... CDD列的數量是可變的，這進一步複雜化了。

這些數據最終將作爲JSON從WCF服務中返回。

dnFolders = from row in dnDataTable.AsEnumerable() 
    group row by new 
    { 
     id = row.Field<string>(1), 
     value = row.Field<string>(2) 

    } into folder 
    select new folder 
    { 
     id = folder.Key.id, 
     value = folder.Key.value 
     folderItem = section.Select(r=>r.Field<String>(3)).ToList() 
    }; 

文件夾類的定義：

public class folder 
{ 
    [DataMember(Name = "id", Order = 1)] 
    public string id { get; set; } 

    [DataMember(Name = "value", Order = 2)] 
    public string value { get; set; } 

    [DataMember(Name = "type", Order = 3)] 
    public string type { get; set; } 

    [DataMember(Name = "sortCol", Order = 4)] 
    public string sortCol { get; set; } 

    [DataMember(Name = "folderItems", Order = 5)] 
    public List<folderItem> folderItems { get; set; } 
} 

folderItem類定義

public class folderItem 
{ 
    [DataMember(Name = "value", Order = 1)] 
    public string value { get; set; } 

    [DataMember(Name = "id", Order = 2)] 
    public string id { get; set; } 

    [DataMember(Name = "type", Order = 2)] 
    public string type { get; set; } 
} 

Answer 1

您的查詢的幾個問題：

• 沒有定義
0123沒有 section變量
• 沒有folderItem財產folder類
• 你應該選擇從每組folderItem對象的名單，但你被選擇的字符串列表

這裏是你的查詢應該怎麼樣子（我不知道什麼是應該去folderItem對象，所以用它初始化屬性type只）：

dnFolders = 
    from row in dnDataTable.AsEnumerable() 
    group row by new 
    { 
     id = row.Field<string>(1), 
     value = row.Field<string>(2) 
    } into g 
    select new folder 
    { 
     id = g.Key.id, 
     value = g.Key.value 
     folderItems = g.Select(r => new folderItem { type = r.Field<string>(3) }) 
         .ToList() 
    }; 

Answer 2

或許有些從lazyberezovsky的回答調整

我相信你的錯誤來自於你的dnFolders varable是一個List？ 在這種情況下，你必須.ToList（）整個查詢

dnFolders = 
    (from row in dnDataTable.AsEnumerable() 
    group row by new 
    { 
     id = row.Field<string>(1), 
     value = row.Field<string>(2) 
    } into g 
    select new folder 
    { 
     id = g.Key.id, 
     value = g.Key.value 
     folderItems = g.Select(r => r.Field<FolderItems>(5) }) 
         .ToList() 
    }).ToList();