實體或複雜類型'FPSDB_newModel.Form_Attachment'不能在LINQ to Entities查詢中構建

Question

我正在使用實體框架DB第一種方法。當我想拉從數據庫中的數據我使用的方法GetForm_AttachmentByAppID當我把這種方法從我的代碼。我得到以下運行時錯誤：

An exception of type 'System.NotSupportedException' occurred in  EntityFramework.SqlServer.dll but was not handled in user code 

Additional information: The entity or complex type 'FPSDB_newModel.Form_Attachment' cannot be constructed in a LINQ to Entities query. 

public partial class Form_Attachment 
{ 
public int Form_AttachmentID { get; set; } 
public Nullable<int> AttachmentCategoryID { get; set; } 
public int ApplicationID { get; set; } 
public string EmployeeID { get; set; } 
public string DocumentName { get; set; } 
public string DocumentSize { get; set; } 
public Nullable<byte> RoleID { get; set; } 
public string Description { get; set; } 
public Nullable<bool> SelectionForExtRev { get; set; } 

public virtual Application Application { get; set; } 
public virtual AttachmentCategory AttachmentCategory { get; set; } 
public virtual Employee Employee { get; set; } 
public virtual Role Role { get; set; } 
}  

上述文件是自動生成的，代碼位於FPSModel.cs下面是我的代碼來拉數據

public List<Form_Attachment> GetForm_AttachmentByAppID(int applicationID) 
{ 
    var context = new FPSDB_newEntities(); 
    var data = (from f in context.Form_Attachment 
       where 
       (
       f.ApplicationID== applicationID 
       ) 
       select new Form_Attachment 
       { 
        Form_AttachmentID = f.Form_AttachmentID, 
        AttachmentCategoryID = f.AttachmentCategoryID, 
        EmployeeID = f.EmployeeID, 
        ApplicationID = f.ApplicationID, 
        DocumentName = f.DocumentName, 
        DocumentSize = f.DocumentSize, 
        RoleID = f.RoleID, 
        Description = f.Description, 
        SelectionForExtRev = f.SelectionForExtRev 
       }).ToList(); 
    return data; 
} 

而且，這裏是我的表的數據庫定義Form_Attachments

CREATE TABLE [dbo].[Form_Attachment](
[Form_AttachmentID] [int] IDENTITY(1,1) NOT NULL, 
[AttachmentCategoryID] [int] NULL, 
[ApplicationID] [int] NOT NULL, 
[EmployeeID] [varchar](10) NOT NULL, 
[DocumentName] [nvarchar](500) NULL, 
[DocumentSize] [nvarchar](50) NULL, 
[RoleID] [tinyint] NULL, 
[Description] [ntext] NULL, 
[SelectionForExtRev] [bit] NULL, 
CONSTRAINT [PK_Form_AttachmentID] PRIMARY KEY CLUSTERED 
(
[Form_AttachmentID] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF,  ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY] 

我已閱讀本The Projection should not be on to a mapped entity 所以，如果我做一類Form_Attachments1就像自動生成Form_Attachments所以會它是一個數據傳輸對象DTO，它是一個正確的方法。

Answer 1

你可以試試這個：

public List<Form_Attachment> GetForm_AttachmentByAppID(int applicationID) 
{ 
    var context = new FPSDB_newEntities(); 
    var data = (from f in context.Form_Attachment 
       where 
       (
       f.ApplicationID== applicationID 
       ) 
       select f).ToList(); 
    return data; 
} 

或本：

data = context.Form_Attachment.Where(p => p.ApplicationID == applicationID).ToList(); 

我現在不能測試，但這應該工作。您不需要映射，因爲'f'表示您的'Form_Attachment'實體類已經存在。如果您使用的是類似'Form_AttachmentDto'的DTO類，那麼您需要像這樣映射它：

public List<Form_AttachmentDto> GetForm_AttachmentByAppID(int applicationID) 
    { 
     var context = new FPSDB_newEntities(); 
     var data = (from f in context.Form_Attachment 
        where 
        (
        f.ApplicationID== applicationID 
        ) 
        select f).Select(p=>new Form_AttachmentDto() 
         { 
         //... 
         // here comes the mapping code 
         //.. 
         } 
        ).ToList(); 
     return data; 
    }