join two datatable and return the result in another data table

Question

Q:

I have two data tables and i wanna to inner join the and return the result in a another datatable through LINQ.

DataTable dt1 = StaffCVDAL.getCourses(int.Parse(Session["emp_num"].ToString()));
DataTable dt2 = cc1lectcrsfilesDAL.ListFiles(int.Parse(Session["emp_num"].ToString()), int.Parse(Session["permission_code"].ToString()));
DataTable dt = from t1 in dt1.AsEnumerable()
               join t2 in dt2.AsEnumerable()
                      on t1["crsnum"] equals t2["crsnum"]
               select new { t1["crsname"],t2["group"] }; //the problem is here .

Is there an explicit need that the result should be a `DataTable`? The LINQ returns a `IEnumerable` of the anonymous type you created. — SWeko, Jul 07 '11 at 11:18
yeah i need the result in a `datatable` and this is the problem. — Anyname Donotcare, Jul 07 '11 at 11:20
hmm, just i wanna the result in more performance way to be the data source of my gridview. — Anyname Donotcare, Jul 07 '11 at 11:34

score 3 · Accepted Answer · edited May 23 '17 at 12:17

3

The problem is that the query expression (LINQ) returns an IEnumerable of the anonymous type you created, instead of a DataTable. IMHO, I prefer working with collections instead of datatables, but if you want to have a DataTable, you can create and populate it yourself from the collection, like this:

var collection = from t1 in dt1.AsEnumerable()
                 join t2 in dt2.AsEnumerable()
                    on t1["crsnum"] equals t2["crsnum"]
                 select new { Name = t1["crsname"], Group = t2["group"] }; 
DataTable result = new DataTable("NameGroups");
result.Columns.Add("crsname", typeof(string));
result.Columns.Add("group", typeof(int));

foreach (var item in collection)
{
   result.Rows.Add(item.Name, item.Group);
}

for more details, and a more general solution, take a look at this.

edited May 23 '17 at 12:17

Community

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answered Jul 07 '11 at 11:29

SWeko

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` select new { t1["crsname"],t2["group"] }` this part make a compile error---> `invalid anonymous type member declarator`. – Anyname Donotcare Jul 07 '11 at 11:36
1

of course it does :). Poor C# cant figure what the names of the fields should be. Will edit the answer. – SWeko Jul 07 '11 at 11:38
thanks a lot but when i trace i find the `collection` is empty while the `inner` yields result !!. – Anyname Donotcare Jul 07 '11 at 12:16

join two datatable and return the result in another data table

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