[英]How to convert sql inner join query into linq to sql query and convert into list
我有以下課程:
public class customRequest
{
public string REQ_STATUS { get; set; }
public DateTime REQ_RVE_DATnTIM { get; set; }
public string EMP_FNAME { get; set; }
public string EVE_CAT_NAME { get; set; }
public string EVE_NAME { get; set; }
}
以及SQL內部連接查詢,它在SQL中運行良好:
SELECT req.REQ_STATUS,req.REQ_RVE_DATnTIM, emp.EMP_FNAME, cat.EVE_CAT_NAME,eve.EVE_NAME from REQUESTS req inner join Employees emp on req.REQ_EMP_ID = emp.ID inner join EVENTCATEGORIES cat on req.REQ_EVE_CAT_ID = cat.ID inner join EVENTS eve on req.REQ_EVE_NAM_ID = eve.ID order by req.REQ_STATUS
我想要的是將它轉換為我的linq到SQL查詢。 下面是我試過的Linq to Sql查詢:
slist = from req in db.REQUESTS
join emp in db.Employees on req.REQ_EMP_ID equals emp.ID
join cat in db.EVENTCATEGORIES on req.REQ_EVE_CAT_ID equals cat.ID
join eve in db.EVENTS on req.REQ_EVE_NAM_ID equals eve.ID
select new { req.REQ_STATUS, req.REQ_RVE_DATnTIM, emp.EMP_FNAME, cat.EVE_CAT_NAME, eve.EVE_NAME };
return slist.ToList();
但它在上次加入時顯示錯誤:
錯誤1無法將類型'System.Linq.IQueryable'隱式轉換為'System.Collections.Generic.List'。 存在顯式轉換(您是否缺少演員?)H:\\ 64bit \\ Project Finalizing \\ Blue_Pumpkin \\ Blue_Pumpkin \\ Admin \\ Requests.aspx.cs 32 25 Blue_Pumpkin
我假設您希望從查詢中返回customRequest
類。 您需要將select語句顯式轉換為customRequest
。
slist = (from req in db.REQUESTS
join emp in db.Employees on req.REQ_EMP_ID equals emp.ID
join cat in db.EVENTCATEGORIES on req.REQ_EVE_CAT_ID equals cat.ID
join eve in db.EVENTS on req.REQ_EVE_NAM_ID equals eve.ID
select new customRequest {
REQ_STATUS = req.REQ_STATUS, req.REQ_RVE_DATnTIM,
EMP_FNAME = emp.EMP_FNAME,
EVE_CAT_NAME = cat.EVE_CAT_NAME,
EVE_NAME = eve.EVE_NAME }).ToList();
return slist;
如果碰巧你確實需要返回一個列表..你需要將返回類型聲明為列表變量並從那里使用ToList()
,如果要返回單行結果集,則可以使用First()
或FirstOrDefault()
您可以將ToList()與linq查詢一起使用:
var slist = (from req in db.REQUESTS
join emp in db.Employees on req.REQ_EMP_ID equals emp.ID
join cat in db.EVENTCATEGORIES on req.REQ_EVE_CAT_ID equals cat.ID
join eve in db.EVENTS on req.REQ_EVE_NAM_ID equals eve.ID
select new select new customRequest {
REQ_STATUS = req.REQ_STATUS,
REQ_RVE_DATnTIM= req.REQ_RVE_DATnTIM,
EMP_FNAME = emp.EMP_FNAME,
EVE_CAT_NAME = cat.EVE_CAT_NAME,
EVE_NAME = eve.EVE_NAME }){
REQ_STATUS = req.REQ_STATUS, req.REQ_RVE_DATnTIM,
EMP_FNAME = emp.EMP_FNAME,
EVE_CAT_NAME = cat.EVE_CAT_NAME,
EVE_NAME = eve.EVE_NAME }).ToList();
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