加載一些數據使用LINQ

Question

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Explicit construction of entity type [MyClass] in query is not allowed

我使用LINQ to SQL的道具 - 我想獲得計數低於2個道具（打開和關閉的任務），但我得到一個異常說我不能加載實體在查詢中，我該如何做到這一點？

我的代碼：

var milestones = ReadOnlySession.All<Milestone>() 
    .Where(x => x.InstructionID == instructionid) 
    .OrderBy(x => x.Name) 
    .Select(x => new Milestone 
    { 
     Name = x.Name, 
     InstructionID = x.InstructionID, 
     Body = x.Body, 
     Deadline = x.Deadline, 
     MilestoneID = x.MilestoneID, 
     TotalClosedTasks = 
      ReadOnlySession.All<InstructionTask>() 
      .Count(c => c.Milestone == x.MilestoneID && !c.IsOpen), 
     TotalOpenTasks = 
      ReadOnlySession.All<InstructionTask>() 
      .Count(c => c.Milestone == x.MilestoneID && c.IsOpen) 
    }) 
    .ToList(); 

錯誤：

消息：在查詢的實體類型 'Surventrix.Domain.Model.Entities.Milestone' 的顯式建築是不允許的。

來源：System.Data.Linq程序

注： ReadOnlySession - 抽象過的數據上下文，爲我提供了所有，單一（基本上得到所有的T實體）

Answer 1

嘗試添加AsEnumerable在訂單條款之後，如果您沒有性能問題，則可以解決問題。

var milestones = ReadOnlySession.All<Milestone>() 
.Where(x => x.InstructionID == instructionid) 
.OrderBy(x => x.Name).AsEnumerable() 
.Select(x => new Milestone 
{ 

Answer 2

我認爲你必須分開里程碑對象的創建從查詢（你還設置了額外的總關閉/打開任務屬性）。在下面的查詢中，從數據庫中的匿名對象，然後*新的里程碑對象被創建。這樣，它仍然是一個單一的查詢，假設ReadOnlySession仍然返回IQueryable的。

var milestones = ReadOnlySession.All<Milestone>() 
    .Where(x => x.InstructionID == instructionid) 
    .OrderBy(x => x.Name) 
    .Select(x => new { 
     Milestone = x, 
     TotalClosedTasks = ReadOnlySession.All<InstructionTask>() 
           .Count(c => c.Milestone == x.MilestoneID && !c.IsOpen) 
     TotalOpenTasks = ReadOnlySession.All<InstructionTask>() 
           .Count(c => c.Milestone == x.MilestoneID && c.IsOpen) 
    }) 
    .AsEnumerable() 
    .Select(x => new Milestone { 
     Name = x.Milestone.Name, 
     InstructionID = x.Milestone.InstructionID, 
     Body = x.Milestone.Body, 
     Deadline = x.Milestone.Deadline, 
     MilestoneID = x.Milestone.MilestoneID, 
     TotalClosedTasks = x.TotalClosedTasks, 
     TotalOpenTasks = x.TotalOpenTask 
    }) 
    .ToList();