LINQ query on DataTable - Could not find an implementation of the query pattern

Question

Can anyone tell me why this doesn't compile? The error is:

Could not find an implementation of the query pattern for source type System.Data.DataTable. Where not found.

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

namespace caLINQ
{
    class Program
    {
        static void Main(string[] args)
        {
            string connectionString = "Data Source=STEVEN-PC\\SQLEXPRESS;Initial Catalog=linqtest;Integrated Security=True;Pooling=False";
            using (System.Data.SqlClient.SqlConnection connection = new System.Data.SqlClient.SqlConnection(connectionString))
            {
                 connection.Open();
                 String cmdText = "select * from customers";
                 System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand(cmdText, connection);
                 System.Data.SqlClient.SqlDataReader dr;
                 dr = cmd.ExecuteReader();
                 DataSet ds = new DataSet();
                 ds.Load(dr, LoadOption.OverwriteChanges, "tab1");
                 DataTable dt = ds.Tables[0];
                 var qy = from c in dt // error is here
                          where c.country == "Italy"
                          select c.name;
            }
            Console.ReadKey();
        }
    }
}

You should be looking at using Linq2Sql instead of filling datatables and querying those. — Magnus
– Magnus, Commented Jun 25, 2012 at 16:32
Hi, welcome. You may consider marking one of the answers as accepted by ticking the big check mark at the left of it. — Gert Arnold
– Gert Arnold, Commented Jun 25, 2012 at 20:49

Magnus · Accepted Answer · 2012-06-25 18:42:22Z

12

Try:

var qy = from c in dt.AsEnumerable()
         where c.Field<string>("country") == "Italy"
         select c.Field<string>("name");

AsEnumerable() will return an IEnumerable<DataRow> that can be used with LINQ.

edited Jun 25, 2012 at 18:42

answered Jun 25, 2012 at 16:26

Magnus

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3 Comments

user1480480 Over a year ago

Thanks Magnus and KreepN. After implementing both your suggestions it worked. It is a trivial app that I am just using to try to get to know LINQ; I figured I would start by filling a DataTable and trying to query it. Now I can move on. SLB

StackOrder Over a year ago

AsEnumerable() is costly

Magnus Over a year ago

@StackOrder not on a DataTable

KreepN · Accepted Answer · 2012-06-25 17:47:37Z

4

Adjust your code to (I'm assuming that your DB columns are "country" and "name):

var qy = from DataRow c in dt.Rows
         where c.Field<string>("country") == "Italy"
         select c.Field<string>("name");

Or

var qy = (from DataRow c in dt.Rows
         where c.Field<string>("country") == "Italy"
         select c.Field<string>("name")).ToList()

For a list of those "names".

answered Jun 25, 2012 at 17:47

KreepN

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