How to solve compare two datatables linq to sql error? - linq

Question

I have two datatables and I need to compare one columns and delete some results .(One Columns=ID)
I use datatable 1 and datatable 2 linq expression.I want to database3.
Common area ise ID:83,21
datatable 1
StudentID ClassNumber No
83 65 1
21 28 15
35 56 87
datatable 2
StudentID BranchNumber
83 3
21 2
datatable 3
StudentID ClassNumber
83 65
21 28
I write this query
public static DataTable Student(Datatable ds,Datatable dc)
{
DataTable StudentDatabaseID1= new DataTable();
DataTable StudentDatabaseID2= new DataTable();
var result=from a in StudentDatabaseID1.AsEnumerable()
join b in StudentDatabaseID2.AsEnumerable()
on a.Field<int>("StudentID") equals b.Field<int>("StudentID")
select
{
StudentID=a.Field<int>("StudentID"),
ClassNumber=a.Field<int>("ClassNumber"),
}
}

Answer 1

I think that you haven't data in StudentDatabaseID1 and StudentDatabaseID2 because they are new variables, maybe you have to use Datatable ds,Datatable dc ???, check it, code works fine like next example:
CODE (this is for LinqPad but you can re-use in your code):
void Main()
{
// Build data
DataTable dt1 = new DataTable();
dt1.Clear();
dt1.Columns.Add("StudentId", typeof(Int32));
dt1.Columns.Add("ClassNumber", typeof(Int32));
dt1.Columns.Add("No", typeof(Int32));
DataRow row1 = dt1.NewRow();
row1["StudentId"] = 83;
row1["ClassNumber"] = 65;
row1["No"] = 1;
dt1.Rows.Add(row1);
row1 = dt1.NewRow();
row1["StudentId"] = 21;
row1["ClassNumber"] = 28;
row1["No"] = 15;
dt1.Rows.Add(row1);
row1 = dt1.NewRow();
row1["StudentId"] = 35;
row1["ClassNumber"] = 56;
row1["No"] = 87;
dt1.Rows.Add(row1);
DataTable dt2 = new DataTable();
dt2.Clear();
dt2.Columns.Add("StudentId", typeof(Int32));
dt2.Columns.Add("BranchNumber", typeof(Int32));
DataRow row2 = dt2.NewRow();
row2["StudentId"] = 83;
row2["BranchNumber"] = 3;
dt2.Rows.Add(row2);
row2 = dt2.NewRow();
row2["StudentId"] = 21;
row2["BranchNumber"] = 2;
dt2.Rows.Add(row2);
// Do query
var result =
from a in dt1.AsEnumerable()
join b in dt2.AsEnumerable() on a.Field<int>("StudentID") equals b.Field<int>("StudentID")
select new {
StudentID=a.Field<int>("StudentID"),
ClassNumber=a.Field<int>("ClassNumber"),
};
// Print result
result.Dump();
}
RESULT