在EF6中只包含部分實體包括

Question

我有一個包含可以具有屬性Id，Name和BinaryData的附件的Punches的模型。

如果我這樣做：

var result = context.PunchSet 
    .Where(p => p.PunchType == punchType && p.Project.Id == projectId) 
    .Include(c => c.Contractor) 
    .Include(c => c.ClearedBy) 
    .Include(c => c.CreatedBy) 
    .Include(a => a.Attachments) 

查詢是慢如molassis因爲附件既可以是很多大。在這種情況下，我需要的是附件的ID和名稱。所以，我想：

var result = context.PunchSet 
    .Where(p => p.PunchType == punchType && p.Project.Id == projectId) 
    .Include(c => c.Contractor) 
    .Include(c => c.ClearedBy) 
    .Include(c => c.CreatedBy) 
    .Include(a => a.Attachments.Select(a2 => new Attachment() { Id=a2.Id, Name=a2.Name}); 

但與此錯誤結束：

The Include path expression must refer to a navigation property defined on the type. Use dotted paths for reference navigation properties and the Select operator for collection navigation properties. Parameter name: path

有不知道這意味着什麼，我一直堅持了幾個小時。如何在結果中包含部分實體？即不要讀取二進制數據。

Answer 1

您可以嘗試在單個查詢中選擇所有需要的屬性，然後將它們一起存儲在內存中。

db.PunchSet 
    .Include(x => x.Contractor) 
    // ... other includes of complete objects 
    // then select properties for partial include 
    .Select(x => new { obj = x, att = x.Attachments.Select(a => new { a.Id, a.Name }) }) 
    // end of database query context 
    .AsEnumerable() 
    // join the results in memory 
    .Select(x => 
    { 
     x.obj.Attachments = x.att.Select(a => new Attachment() { Id = a.Id, Name = a.Name }).ToList(); 
     return x.obj; 
    }); 

Answer 2

您可以嘗試如下所示。

var result = from p in context.PunchSet 
       where (p.PunchType == punchType && p.Project.Id == projectId) 
       select new { 
          p, 
          Contractor=p.Contractor, 
          ClearedBy =p.ClearedBy, 
          CreatedBy=p.CreatedBy, 

          Attachments= from a in p.Attachments 
             select new { 
                Id= a.Id, 
                Name =a.Name, 
                }, 

      }; 

var result2 = result.AsEnumerable() 
        .Select(c => c.p); 

之後，你想:)

foreach(var r in result2) 
{ 
    foreach(var a in r.Attachments) 
    { 
     //your code; 
    } 
}