Convert complex nested selects in Entity Framework query - mysql

Question

I need to create a table in View by this View Model:
public class ApplicationContentViewModel
{
public BPMSPARS.Models.MySql.application application {get; set;}
public BPMSPARS.Models.MySql.content content { get; set; }
public BPMSPARS.Models.MySql.app_delegation app_delegation { get; set; }
}
But the query for creating new Table is very complex.
I use this query in MySQL, and I can get correct results by using it.
SELECT APP_UID, (SELECT CON_VALUE FROM content WHERE CON_CATEGORY = 'PRO_TITLE' AND CON_ID =
(SELECT PRO_UID from app_delegation WHERE del_thread_status='open' and USR_UID = '00000000000000000000000000000001' AND APP_UID = '9134216305aaaea1b67c4e2096663219')) AS TASK_NAME,
(SELECT CON_VALUE FROM content WHERE CON_CATEGORY = 'TAS_TITLE' AND CON_ID =
(SELECT TAS_UID from app_delegation WHERE del_thread_status='open' and USR_UID = '00000000000000000000000000000001' AND APP_UID = '9134216305aaaea1b67c4e2096663219')) AS PROCESS_NAME FROM app_delegation
WHERE del_thread_status='open' and USR_UID = '00000000000000000000000000000001' AND APP_UID = '9134216305aaaea1b67c4e2096663219'
But, I have to convert this query in linq or EF in MVC.
How Can I write This Query in Entity Framework query?
And How Can I display results in View?

Answer 1

Your SQL query seems (very) peculiar to me, as it is quite redundant. I am going to assume the sub-queries return a single value and enforce it with LINQ.
First I pulled out the common sub-query over app_delegation:
var USR_APP_Delegation = from a in app_delegation
where a.del_thread_status == "open" &&
a.USR_UID == "00000000000000000000000000000001" &&
a.APP_UID == "9134216305aaaea1b67c4e2096663219"
select a;
In LINQ it is easy to combine the two UID queries into one query:
var UIDs = (from a in USR_APP_Delegation
select new { a.PRO_UID, a.TAS_UID })
.Single();
Now you can do the name subqueries:
var TASK_NAME = (from c in content
where c.CON_CATEGORY == "PRO_TITLE" &&
c.CON_ID == UIDs.PRO_UID
select c.CON_VALUE)
.Single();
var PROCESS_NAME = (from c in content
where c.CON_CATEGORY == "TAS_TITLE" &&
c.CON_ID == UIDs.TAS_UID
select c.CON_VALUE)
.Single();
Then you can put all the queries together for the final result:
var ans = (from a in USR_APP_Delegation
select new {
a.APP_UID,
TASK_NAME,
PROCESS_NAME
})
.Single();
Again, this makes it obvious that your e.g. returning APP_UID when you know exactly what it is, and you are combining TASK_NAME and PROCESS_NAME into a query for no real advantage.
I would suggest using join against content makes a much more understandable query (even in SQL) and makes it clearer what is being returned:
var names = from a in app_delegation
join cpro in content on new { CON_ID = a.PRO_UID, CON_CATEGORY = "PRO_TITLE" } equals new { cpro.CON_ID, cpro.CON_CATEGORY }
join ctas in content on new { CON_ID = a.PRO_UID, CON_CATEGORY = "TAS_TITLE" } equals new { ctas.CON_ID, ctas.CON_CATEGORY }
where a.del_thread_status == "open" &&
a.USR_UID == "00000000000000000000000000000001" &&
a.APP_UID == "9134216305aaaea1b67c4e2096663219"
select new {
a.APP_UID,
Task_Name = ctas.CON_VALUE,
Process_Name = cpro.CON_VALUE
};