无法离开JOIN linq查询工作！

Question

我一直在看下面的帖子，并试图将其应用到矿山，但没有运气： LINQ Inner-Join vs Left-Join

我有以下查询将返回0条记录，每次我运行它：

 var tasks = from tt in d.luProjectTaskTypes 
        join cbt in d.CostByTasks 
         on tt.ProjectTaskTypeID equals cbt.ProjectTaskTypeID into temp 
        from cbt in temp.DefaultIfEmpty() 
        where cbt.ProposalID == Convert.ToInt32(this.StateItems["PropNumber"]) || cbt.ProposalID == null 
        select new 
        { 
         ProposalId = (cbt.ProposalID == null ? Convert.ToInt32(this.StateItems["PropNumber"]) : cbt.ProposalID), 
         TaskId = tt.ProjectTaskTypeID, 
         CostByTaskId = (cbt.CostByTaskID == null ? 0 : cbt.CostByTaskID), 
         TypeOfWork = tt.ProjectTaskType, 
         AmountRequested = (cbt.AmountRequested == null ? 0 : cbt.AmountRequested), 
         CostShare = (cbt.CostShareAmount == null ? 0 : cbt.CostShareAmount) 
        }; 

其中luProjectTaskTypes是具有选项列表的查找表。我希望为此表中的每个条目返回一条记录，无论它是否在CostByTasks中匹配，但我总是得到0.我做错了什么？

UPDATE：

这是SQL是generating-

SELECT 
    (CASE 
     WHEN ([t1].[ProposalID]) IS NULL THEN @p1 
     ELSE [t1].[ProposalID] 
    END) AS [ProposalId], [t0].[ProjectTaskTypeID] AS [TaskId], 
    (CASE 
     WHEN ([t1].[CostByTaskID]) IS NULL THEN @p2 
     ELSE [t1].[CostByTaskID] 
    END) AS [CostByTaskId], [t0].[ProjectTaskType] AS [TypeOfWork], 
    (CASE 
     WHEN [t1].[AmountRequested] IS NULL THEN CONVERT(Decimal(33,4),@p3) 
     ELSE CONVERT(Decimal(33,4),[t1].[AmountRequested]) 
    END) AS [AmountRequested], 
    (CASE 
     WHEN [t1].[CostShareAmount] IS NULL THEN CONVERT(Decimal(33,4),@p4) 
     ELSE CONVERT(Decimal(33,4),[t1].[CostShareAmount]) 
    END) AS [CostShare] 
FROM [frgprop].[luProjectTaskType] AS [t0] 
LEFT OUTER JOIN [frgprop].[CostByTask] AS [t1] ON [t0].[ProjectTaskTypeID] = [t1].[ProjectTaskTypeID] 
WHERE ([t1].[ProposalID] = @p0) OR (([t1].[ProposalID]) IS NULL) 

Answer 1

不知道这是否会帮助，但你可以尝试你的where子句移动到一起 -

var tasks = from tt in d.luProjectTaskTypes 
      join cbt in d.CostByTasks 
       on new {ptid = tt.ProjectTaskTypeID, pid = cbt.ProposalID } equals new { ptid = cbt.ProjectTaskTypeID, pid = Convert.ToInt32(this.StateItems["PropNumber"] } into temp 
      from cbt in temp.DefaultIfEmpty() 
      select new 
      { 
       ProposalId = (cbt.ProposalID == null ? Convert.ToInt32(this.StateItems["PropNumber"]) : cbt.ProposalID), 
       TaskId = tt.ProjectTaskTypeID, 
       CostByTaskId = (cbt.CostByTaskID == null ? 0 : cbt.CostByTaskID), 
       TypeOfWork = tt.ProjectTaskType, 
       AmountRequested = (cbt.AmountRequested == null ? 0 : cbt.AmountRequested), 
       CostShare = (cbt.CostShareAmount == null ? 0 : cbt.CostShareAmount) 
      }; 

你需要担心检查cbt.ProposalID == null，它应该产生这种SQL代替 -

... FROM [frgprop].[luProjectTaskType] AS [t0] 
    LEFT OUTER JOIN [frgprop].[CostByTask] AS [t1] ON [t0].[ProjectTaskTypeID] = [t1].[ProjectTaskTypeID] AND [t1].[ProposalID] = @p0 

更新： 下面是编译的更新版本。一些小的变化使它工作。

var tasks = from tt in d.luProjectTaskTypes 
         join cbt in d.CostByTasks 
          on new {tt.ProjectTaskTypeID, ProposalID = Convert.ToInt32(this.StateItems["PropNumber"]) } equals new {cbt.ProjectTaskTypeID, cbt.ProposalID} into temp 
         from cbt in temp.DefaultIfEmpty() 
         select new 
         { 
          ProposalId = (cbt.ProposalID == null ? Convert.ToInt32(this.StateItems["PropNumber"]) : cbt.ProposalID), 
          TaskId = tt.ProjectTaskTypeID, 
          CostByTaskId = (cbt.CostByTaskID == null ? 0 : cbt.CostByTaskID), 
          TypeOfWork = tt.ProjectTaskType, 
          AmountRequested = (cbt.AmountRequested == null ? 0 : cbt.AmountRequested), 
          CostShare = (cbt.CostShareAmount == null ? 0 : cbt.CostShareAmount) 
         }; 

Answer 2

您的问题是在WHERE子句

当你LEFT JOIN表，这很好，但如果你在LEFT-JOINED表上设置了标准，它基本上把它变成了一个INNER JOIN。你应该允许Nulls通过这个。

where cbt.ProposalID == Convert.ToInt32(this.StateItems["PropNumber"]) OR cbt.ProposalID is NULL 

我不知道怎么样为NULL语法 - 也许必须db.null(field)，等等 - 你必须检查上;但这个概念是有效的。