Linq加入返回的父母，即使當孩子爲null

Question

我想要選擇所有的行，其中假2是空的，所有的行與虛假2加入 下面的代碼沒有問題，但我想在選擇LINQ查詢提高效率。

var rows = (
      from a in crmLinqContext.fakeSet 
      join b in crmLinqContext.fake2Set on a.fake2.Id equals b.Id 
      join c in crmLinqContext.fake3Set on b.field equals c.field 
      where c.anotherField == "THIS_BIT_OF_TEXT" 
      select a); 

List<myObject> objects = new List<myObject>(); 
foreach(var row in rows) 
{ 
    objects.Add(row); 
} 
rows = (
    from a in crmLinqContext.fakeSet 
    where s.fake2 == null 
    select a); 

foreach (var row in rows) 
{ 
    objects.Add(row); 
} 
return objects; 

Answer 1

使用左連接在LINQ類似下面，它不是測試，但它的作用是，它左外連接fakeSet和fakeSet2。

var rows = 
    from a in crmLinqContext.fakeSet 
    join b in crmLinqContext.fake2Set on a.fake2.Id equals b.Id into subset 
    from b in subset.DefaultIfEmpty() 
    join c in crmLinqContext.fake3Set on b.field equals c.field 
    where c.anotherField == "THIS_BIT_OF_TEXT" 
    select a; 

Answer 2

var rows = (
      from a in crmLinqContext.fakeSet 
      join b in crmLinqContext.fake2Set on a.Id equals b.Id 
      join c in crmLinqContext.fake3Set on b.field equals c.field 
      where c.anotherField == "THIS_BIT_OF_TEXT" 
      select a) 
      .Concat(
      from a1 in crmLinqContext.fakeSet 
      where a1.fake2 == null 
      select a1);