how to use (dynamic)null concept to this query - linq

Question

i wan to bind grid view with different kinds of conditions show here i'm use (dynamic)null concept for query declaration but at end of rest i can't getting field that associated with query.
here i put my code :
public void FillGrid(string GroupByText, string ColumnName, string SearchText)
{
using (DataClassesDataContext db = new DataClassesDataContext())
{
var query = (dynamic)null;
switch (GroupByText)
{
case "Enquiry":
query = db.Enquiries.Where(i => i.enttype_id.Equals("1")).OrderByDescending(i => i.Created_date).Select(i => new
{
Ref_no = i.Ref_no,
Name = db.Parties.Where(p => p.Id.Equals(i.party_id)).Select(p => p.Name).SingleOrDefault(),
StatusName = db.Status.Where(s => s.Id.Equals(i.status_id)).Select(s => s.StatusName).SingleOrDefault(),
CategoryName = db.Categories.Where(c => c.Id.Equals(i.category_id)).Select(c => c.category_name).SingleOrDefault(),
IsUregent = i.IsUregent,
Created_date = i.Created_date
}).FilterForColumn(ColumnName,SearchText).ToList();
break;
case "Visit":
query = db.Enquiries.Where(i => i.enttype_id.Equals("2")).OrderByDescending(i => i.Created_date).Select(i => new
{
Ref_no = i.Ref_no,
Name = db.Parties.Where(p => p.Id.Equals(i.party_id)).Select(p => p.Name).SingleOrDefault(),
StatusName = db.Status.Where(s => s.Id.Equals(i.status_id)).Select(s => s.StatusName).SingleOrDefault(),
CategoryName = db.Categories.Where(c => c.Id.Equals(i.category_id)).Select(c => c.category_name).SingleOrDefault(),
IsUregent = i.IsUregent,
Created_date = i.Created_date
}).FilterForColumn(ColumnName,SearchText).ToList();
break;
default:
query = db.Enquiries.OrderByDescending(i => i.Created_date).Select(i => new
{
Ref_no = i.Ref_no,
Name = db.Parties.Where(p => p.Id.Equals(i.party_id)).Select(p => p.Name).SingleOrDefault(),
StatusName = db.Status.Where(s => s.Id.Equals(i.status_id)).Select(s => s.StatusName).SingleOrDefault(),
CategoryName = db.Categories.Where(c => c.Id.Equals(i.category_id)).Select(c => c.category_name).SingleOrDefault(),
IsUregent = i.IsUregent,
Created_date = i.Created_date
}).FilterForColumn(ColumnName, SearchText).ToList();
break;
}
int count = 0;
DataSet myDataSet = new DataSet();
DataTable dt = new DataTable();
dt.Columns.Add(new DataColumn("Ref_no", typeof(string)));
dt.Columns.Add(new DataColumn("Name", typeof(string)));
dt.Columns.Add(new DataColumn("StatusName", typeof(int)));
dt.Columns.Add(new DataColumn("CategoryName", typeof(string)));
dt.Columns.Add(new DataColumn("IsUregent", typeof(bool)));
dt.Columns.Add(new DataColumn("Created_date", typeof(DateTime)));
foreach (var item in query)
{
if (item != null)
{
DataRow dr = dt.NewRow();
dr["Ref_no"] = item.//not founding field that
}
}
}
}

Answer 1

what is the return type of .FilterForColumn(ColumnName,SearchText) ?
if it does just filtering, without changing the Data Type, i think you can use this:
var query = Enumerable.Repeat(new
{
Ref_no = string.Empty,
Name = string.Empty,
StatusName = default(int),
CategoryName = string.Empty,
IsUregent = default(bool),
Created_date = default(DateTime)
}, 0)
.ToList();
instead of this:
var query = (dynamic)null;
and probably this can solve your problem