將sql查詢轉換爲具有複雜左連接的linq

Question

我是Linq連接的新手。

我有一個SQL查詢如下。請幫我把它轉換成linq。

select c.mem_id, 
c.po_start, 
c.po_end, 
isnull(pp.new_policy_code,c.policy_no) 
from claims_data c 
left join tob_policy tp on (c.subgroup_id =tp.subgroup_id and c.category_id = tp.category_id 
    and c.service_from_date Between tp.Start_Date And isnull (tp.End_Date, 
cast(GETDATE() as date))) 
    Left Join Tob_Policy_Period Pp On (Pp.Policy_Id = tp.Policy_Id And 
c.service_from_date Between Pp.Start_Date And Pp.End_Date) 
    where c.cid = 13 
    and c.g_id = 19013 
    and c.mem_id = '123' 
    and c.code ='555' 

Answer 1

嘗試使用此代碼：

var results = (from c in yourmodelentity.claims_data 
         join tp in yourmodelentity.tob_policy on c.subgroup_id equals tp.subgroup_id && c.category_id equals tp.category_id && c.service_from_date Between tp.Start_Date && isnull (tp.End_Date, datetime.now))) 
         join Pp in yourmodelentity.Tob_Policy_Period on Pp.Policy_Id equals tp.Policy_Id && c.service_from_date Between Pp.Start_Date && Pp.End_Date 
         where c.cid = 13 && c.g_id = 19013 && c.mem_id = '123' && c.code ='555' 
         select new 
         { 
          c.mem_id, 
          c.po_start, 
          c.po_end 
         }).ToList(); 

Answer 2

嘗試用下面的代碼：

var results = (from c in modelentity.claims_data 
          join tp in modelentity.tob_policy on new { first = c.subgroup_id, second= c.category_id } equals new { first = tp.subgroup_id, second = tp.category_id } into tpjoin 
          from tplj in tpjoin.DefaultIfEmpty() 
          join pp in modelentity.Tob_Policy_Period on new { first = tplj.Policy_Id ?? 0 } equals new { first = Pp.Policy_Id } into ppjoin 
          from pplj in tpjoin.DefaultIfEmpty() 
         where ((c.service_from_date) >= tplj.Start_Date && (c.service_from_date) <= (tplj.End_Date ?? DateTime.Now)) && 
         ((c.service_from_date) >= pplj.Start_Date && (c.service_from_date) <= pplj.End_Date) && 
         (c.cid = 13 && c.g_id = 19013 && c.mem_id = "123" && c.code = "555") 
         select new 
         { 
          c.mem_id, 
          c.po_start, 
          c.po_end, 
          policy_no = (pplj != null ? (pplj.new_policy_code ?? c.policy_no) : c.policy_no) 
         }).ToList();