Left Join in Linq gives an error [Resolved]

Posted by Sharpcnet under LINQ on 12/17/2013 | Points: 10 | Views : 1225 | Status : [Member] | Replies : 4

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Table : tblEmp 

EmpId  EmpName ManagerId
101    john     Null
102    jack     101

The foll. query gives an error that the materialized value is null. Where am i going wrong. Please note that the EmpId & ManagerId are actually GUIDs in table.

Using c#, linq to entities

public DataTable GetData(guid id)
{
  var qry = from e in MYDB.tblEmps.where(e=>e.EmpId==id)
            join m in MYDB.tblEmps on e.ManagerId equals m.EmpId into emp_mgr
            from m in emp_mgr.DefaultIfEmpty()
            select new
            {
              name = m.empname ?? string.empty,
              id = e.managerid  //also tried e.managerid ?? guid.empty
            }
   DataTable dt = qry.ToDataTable();
   return dt;
}

[Resolved]

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Posted by: Sharpcnet on: 12/18/2013 [Member] Starter | Points: 25

0	That doesnt compile because empid is guid and i cant pass an int. But thank you anyways. Someone suggested this and it worked... name = m!=null && m.empname!=null ? m.empname : string.empty, Sharpcnet, if this helps please login to Mark As Answer. \| Alert Moderator

Posted by: vishalneeraj-24503 on: 12/17/2013 [Member] [MVP] Platinum | Points: 25

0	Hi, Why are you passing Guid as a parameter in function, you can pass integer or string instead of Guid as below:- public DataTable GetData(int id) { var qry = from e in MYDB.tblEmps.where(e=>e.EmpId==id) join m in MYDB.tblEmps on e.ManagerId = m.EmpId into emp_mgr from m in emp_mgr.DefaultIfEmpty() select new { name = m.empname ?? string.empty, id = e.managerid //also tried e.managerid ?? guid.empty } DataTable dt = qry.ToDataTable(); return dt; } Now check. Sharpcnet, if this helps please login to Mark As Answer. \| Alert Moderator

Hi,
Why are you passing Guid as a parameter in function, you can pass integer or string instead of Guid as below:-

public DataTable GetData(int id)

{

  var qry = from e in MYDB.tblEmps.where(e=>e.EmpId==id)

            join m in MYDB.tblEmps on e.ManagerId = m.EmpId into emp_mgr

            from m in emp_mgr.DefaultIfEmpty()

            select new

            {

              name = m.empname ?? string.empty,

              id = e.managerid  //also tried e.managerid ?? guid.empty

            }

   DataTable dt = qry.ToDataTable();

   return dt;

}

Now check.

Sharpcnet, if this helps please login to Mark As Answer. | Alert Moderator

Posted by: Sharpcnet on: 12/18/2013 [Member] Starter | Points: 25

0	"Please note that the EmpId & ManagerId are actually GUIDs in table. " Sharpcnet, if this helps please login to Mark As Answer. \| Alert Moderator

Posted by: vishalneeraj-24503 on: 12/18/2013 [Member] [MVP] Platinum | Points: 25

0	Yes that is fine, but do you know, GUID value is changing again and again. Did you try above code which i modified? Sharpcnet, if this helps please login to Mark As Answer. \| Alert Moderator

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