linq to sql: issue with linq query - visual-studio-2010

Question

I have two tables
EmpInf
EmpId,
EmpName,
Salary,
DepartNumber.
Dept
DeptNo,
Deptname,
I also have a listview1 and dropdownlist1 which is bound to EmpInf.EmpName
While passing a particular query
FilterControl.DataClasses1DataContext obj = new DataClasses1DataContext();
protected void DropDownList1_SelectedIndexChanged1(object sender, EventArgs e)
{
var a = from r in obj.EmpInfs join s in obj.Dept1s on r.DeptNumber equals s.DeptNo where r.EmpName == "'" + DropDownList1.SelectedValue + "'" select s;
ListView1.DataSource = a;
ListView1.DataBind();
}
Whenever I select a particular name from a dropdownlist, it returns No data was returned. What particular code am I missing or is there any other error?

Answer 1

Put a breakpoint in SelectedIndexChanged1 and look at the value of SelectedValue to make sure DropDownList1.SelectedValue has the Employee name. You can also try DropDownList1.SelectedText.
string selected = DropDownList1.SelectedValue.ToString();
// e = employee | d = department
var query =
from e in obj.EmpInfs
join d in obj.Dept1s on e.DeptNumber equals d.DeptNo
where e.EmpName == "'" + DropDownList1.SelectedValue + "'"
select d;
Change this line:
where e.EmpName == "'" + DropDownList1.SelectedValue + "'"
to this one:
where e.EmpName == selected
OK, my last attempt here... Do this before databinding:
ListView1.DataSource = query.ToList();

Answer 2

Most likely the problem here is with your addition of the single quotes on the search criteria in your Where clause:
var a = from r in obj.EmpInfs
join s in obj.Dept1s on r.DeptNumber equals s.DeptNo
where r.EmpName == "'" + DropDownList1.SelectedValue + "'"
select s;
Assuming DropDownList1.SelectedValue is "Smith" then your generated sql will be along the lines of:
SELECT *
FROM <tables>
WHERE EmpName = ''Smith''
Notice the double single quotes. To double check this, put a breakpoint after your query is generated and then call .ToString() on it to get the equivalent TSQL. To fix this, remove the "'" from your LINQ query as that will be automatically added for string parameters:
var a = from r in obj.EmpInfs
join s in obj.Dept1s on r.DeptNumber equals s.DeptNo
where r.EmpName == DropDownList1.SelectedValue
select s;