Convert complex nested selects in Entity Framework query

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?

Is it necessary for additional information? – Lili.brh Mar 18 '18 at 10:22 — Lili.brh, Mar 18 '18 at 10:22
If that's your usr_id, I'm leaving this one well alone – Strawberry Mar 18 '18 at 10:32 — Strawberry, Mar 18 '18 at 10:32

NetMage · Accepted Answer · 2018-03-23T21:21:30.850

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
            };

How can i show these items in view by foreach loop?I pass ans to view. — Lili.brh, Mar 28 '18 at 07:24
Depending on what you are doing, you don't need a loop, e.g. you can just use `names` as a data source for a Repeater or Grid or whatever. — NetMage, Mar 28 '18 at 19:18
I would suggest asking another question. That is too broad to answer. — NetMage, Mar 29 '18 at 17:34

Convert complex nested selects in Entity Framework query

1 Answers1