如何使用LINQ連接三個數據源？

Question

我有以下幾點：

var questions = questionService.Details(pk, rk); 
var topics = contentService.GetTitles("0006000") 
       .Where(x => x.RowKey.Substring(2, 2) != "00"); 
model = (
    from q in questions 
    join t in topics on q.RowKey.Substring(0, 4) equals t.RowKey into topics2 
    from t in topics2.DefaultIfEmpty() 
    select new Question.Grid { 
     PartitionKey = q.PartitionKey, 
     RowKey = q.RowKey, 
     Topic = t == null ? "No matching topic" : t.Title, 
     ... 

現在我需要添加以下內容：

var types = referenceService.Get("07"); 

哪裏有questions.type和types.RowKey

之間的聯繫是沒有辦法，我可以鏈接的方式這第三個數據源，並且如果在類型表中沒有匹配的話，它會給出一條消息「No matching type」？我的問題是我只是不確定如何做下一個加入。

Answer 1

我相信你可以加入的結果，先與第三數據源連接：

var questions = questionService.Details(pk, rk); 
var topics = contentService.GetTitles("0006000") 
       .Where(x => x.RowKey.Substring(2, 2) != "00"); 
var types = referenceService.Get("07"); 

model = (
    from q in questions 
    join t in topics on q.RowKey.Substring(0, 4) equals t.RowKey into topics2 
    from t in topics2.DefaultIfEmpty() 
    join type in types on q.type equals type.RowKey into types2 
    from type in types2.DefaultIfEmpty() 
    select new Question.Grid { 
     PartitionKey = q.PartitionKey, 
     RowKey = q.RowKey, 
     Topic = t == null ? "No matching topic" : t.Title, 
     Type = type == null ? "No matching type" : type.Title, 
     ... 

Answer 2

 var questions = questionService.Details(pk, rk); 
     var topics = contentService.GetTitles("0006000") 
         .Where(x => x.RowKey.Substring(2, 2) != "00"); 
     var types = referenceService.Get("07"); 
     model = (from q in questions 
      join t in topics on q.RowKey.Substring(0, 4) equals t.RowKey into topics2 
      from t in topics2.DefaultIfEmpty()) 
      select new Question.Grid { 
       PartitionKey = q.PartitionKey, 
       RowKey = q.RowKey, 
       Topic = t == null ? "No matching topic" : t.Title, 
       ... 
      }).Union 
      (from a in types 
      join q in questions on q.type equals a.RowKey 
      where a.ID != null 
      select new Question.Grid { 
        PartitionKey = q.PartitionKey, 
        RowKey = q.RowKey, 
        Topic = t == null ? "No matching topic" : t.Title, 
        ... 
      })