Question

I have the following datatables

table1:

+-----------+------+------+
| catalogid | name | snum |
+-----------+------+------+
|       353 | xx   |    4 |
|       364 | yy   |    3 |
|       882 | zz   |    3 |
|       224 | mm   |   71 |
|       999 | kk   |  321 |
|        74 | kk   |    4 |
|        54 | ii   |    5 |
|        11 | u    |    6 |
|        23 | yy   |    6 |
+-----------+------+------+

table2:

+-----------+----------+--------------+
| catalogid | numitems | ignoreditems |
+-----------+----------+--------------+
|       353 |        4 |            0 |
|       364 |       10 |            0 |
|       882 |        2 |            0 |
|       224 |        0 |            7 |
+-----------+----------+--------------+

Using LINQ I want to join them and copy the result to a new datatable. They both share catalogid, and in the result it should only display the records that their catalogid exist in table2

result:

+-----------+------+------+-----------+---------------+
| catalogid | name | snum | numitems  | ignoreditems  |
+-----------+------+------+-----------+---------------+
|       353 | xx   |    4 |         4 |             0 |
|       364 | yy   |    3 |        10 |             0 |
|       882 | zz   |    3 |         2 |             0 |
|       224 | mm   |   71 |         0 |             7 |
+-----------+------+------+-----------+---------------+

Here is my attempt but it’s not working:

 Dim query = From a In oresult.AsEnumerable
             Group Join b In products.AsEnumerable
             On a.Field(Of Integer)("catalogid") Equals b.Field(Of Integer)("catalogid")
             Into Group
 query.copytodatatable

CopyToDatatable is not working, and I can’t figure out why

Answer 1

CopyToDataTable() only works when your query returns an IEnumerable<‘DataRow>. In your query, you are returning an anonymous type. Anonymous types don’t carry the extension method for CopyToDataTable().

You can create a table using the ConvertToDataTable extension listed below. You’ll have to convert it to VB.NET (there are converters out there if you google).

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using Common;

namespace TestConsole
{
    public class Linq_join_2_datatables_that_share_a_column_and_put_result_in_new_datatable
    {
        public class Table1
        {
            public int CatalogId { get; set; }
            public string Name { get; set; }
            public int SNum { get; set; }
        }

        public class Table2
        {
            public int CatalogId { get; set; }
            public int NumItems { get; set; }
            public int IgnoredItems { get; set; }
        }

        public static void Start()
        {
            DataTable table1 = new DataTable();
            table1.Columns.Add("catalogid", typeof(int));
            table1.Columns.Add("name", typeof(string));
            table1.Columns.Add("snum", typeof(int));
            DataRow row = table1.Rows.Add(353, "xx", 4);

            DataTable table2 = new DataTable();
            table2.Columns.Add("catalogid", typeof(int));
            table2.Columns.Add("numitems", typeof(int));
            table2.Columns.Add("ignoreditems", typeof(int));
            table2.Rows.Add(353, 4, 0);

            var query = (from t1 in table1.AsEnumerable()
                        join t2 in table2.AsEnumerable() on t1.Field<int>("catalogid") equals t2.Field<int>("catalogid")
                        select new
                        {
                            catalogid = t1.Field<int>("catalogid"),
                            name = t1.Field<string>("name"),
                            snum = t1.Field<int>("snum"),
                            numitems = t2.Field<int>("numitems"),
                            ignoreditems = t2.Field<int>("ignoreditems")
                        }).ToList();

            DataTable table3 = query.ConvertToDataTable();      
        }
    }    
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.ComponentModel;
using System.Reflection;

namespace Common
{
    public static class DataTableExtensions
    {
        public static DataTable ConvertToDataTable<T>(this IList<T> data)
        {
            PropertyDescriptorCollection properties =
                TypeDescriptor.GetProperties(typeof(T));
            DataTable table = new DataTable();
            foreach (PropertyDescriptor prop in properties)
                table.Columns.Add(prop.Name, Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType);
            foreach (T item in data)
            {
                DataRow row = table.NewRow();
                foreach (PropertyDescriptor prop in properties)
                    row[prop.Name] = prop.GetValue(item) ?? DBNull.Value;
                table.Rows.Add(row);
            }
            table.AcceptChanges();
            return table;
        }

    }
}