Linq to EF - 從EDM C填充一個（相當簡單）的分層對象＃

Question

我想使用linq將一個父對象及其子項（一級子項）填充到EF。 （最終）方法將採用父輸入並返回項目及其所有子項。我發佈的示例使用parented == null來獲取頂級項目。試圖讓它首先工作。

我發佈了創建表語句，並在本文末尾添加了示例數據。

我想要填充的對象稱爲AttributeObject。它包含一個名稱（這是數據庫中的「值」列）以及它的子項列表。

public class AttributeObject 
    { 
     [DataMember] 
     public string Name { get; set; } 

     [DataMember] 
     public int ID { get; set; } 
     [DataMember] 
     public List<AttributeObject> Children { get; set; } 
    } 

我正在努力加載孩子。我的代碼是：

 var attributes = 
      (from attr in model.CategoryAttributes.Include(c => c.Children) 
      where attr.ParentID == null 
      select new AttributeObject() 
      { 
       Name = attr.Value, 
       ID = attr.ID, 
       Children = attr.Children.AsEnumerable().ToList<AttributeObject>() 
      }); 

我得到的錯誤是，它不能從的CategoryAttribute（實體類型）轉換爲AttributeObject

非常感謝

SQL表：

CREATE TABLE [CategoryAttribute](
     [ID] [int] IDENTITY(1,1) NOT NULL, 
     [Value] [varchar](1000) NOT NULL, 
     [ParentID] [int] NULL, 
     [Weight] [int] NULL, 
    CONSTRAINT [PK_ECM_CategoryAttributeValues] PRIMARY KEY CLUSTERED 
    (
     [ID] ASC 
    )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY] 
    ) ON [PRIMARY] 

    SET IDENTITY_INSERT [CategoryAttribute] ON 

    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (1, N'Document Properties', NULL, 1) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (2, N'Document Group', 1, 1) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (3, N'Document Type', 2, 1) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (12, N'IS Agreement', 2, 5) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (13, N'IS Guides', 2, 5) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (70, N'Service Agreement', 12, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (71, N'Software Licensing', 12, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (72, N'SOW', 12, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (73, N'Support Contracts', 12, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (74, N'Administration Guide', 13, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (75, N'Developer Guide', 13, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (76, N'Installation Guide', 13, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (77, N'Procedure', 13, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (78, N'Release Notes', 13, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (79, N'Training Manual', 13, 8) 
    INSERT [CategoryAttribute] ([ID], [Value], [ParentID], [Weight]) VALUES (80, N'User Guide', 13, 8) 
    SET IDENTITY_INSERT [CategoryAttribute] OFF 
    ALTER TABLE [CategoryAttribute] WITH CHECK ADD CONSTRAINT [FK_ECM_CategoryAttributeValues_ECM_CategoryAttributeValues] FOREIGN KEY([ParentID]) 
    REFERENCES [CategoryAttribute] ([ID]) 
    ALTER TABLE [CategoryAttribute] CHECK CONSTRAINT [FK_ECM_CategoryAttributeValues_ECM_CategoryAttributeValues] 

Answer 1

像這樣的東西應該工作：

   var attributes = 
           (from attr in model.CategoryAttributes.Include(c => c.Children) 
           where attr.ParentID == null 
//Edited Here 
           select new 
      { 
       Name = attr.Value, 
       ID = attr.ID, 
       Children = attr.Children 
       .Select(c => new AttributeObject() { Name = c.Value, ID = c.ID }) 
         .ToList() 
      }) 
    //and Here execute the query with LINQ to Entities 
    .AsEnumerable() 
    //correctly cast to AttributeObject with LINQ to Object 
       .Select(n => 
        new AttributeObject() { 
       Name=n.Name, 
       ID=n.ID, 
       Children=n.Children 

      }).ToList();