using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Xml.Serialization;

using System.IO;

using System.Diagnostics;

using System.Xml;

using System.Collections.ObjectModel;

using System.Threading;

using System.ComponentModel;

using System.Xml.Linq;

using System.Reflection;

using System.Data;  // For System.Data.DataTableExtensions

using System.Xml.Schema;

using System.Runtime.Serialization;

using System.Globalization;

​

    public class TestClass

    {

        public static string GetDataSetXsd()

        {

            var xsd = @"<?xml version=""1.0"" encoding=""utf-16""?>

            <xs:schema id=""NewDataSet"" xmlns="""" xmlns:xs=""http://www.w3.org/2001/XMLSchema"" xmlns:msdata=""urn:schemas-microsoft-com:xml-msdata"">

               <xs:element name=""NewDataSet"" msdata:IsDataSet=""true"" msdata:UseCurrentLocale=""true"">

                  <xs:complexType>

                     <xs:choice minOccurs=""0"" maxOccurs=""unbounded"">

                        <xs:element name=""Table"">

                           <xs:complexType>

                              <xs:sequence>

                                 <xs:element name=""SourceID"" type=""xs:string"" minOccurs=""0""/>

                                 <xs:element name=""Caption"" type=""xs:string"" minOccurs=""0""/>

                              </xs:sequence>

                           </xs:complexType>

                        </xs:element>

                     </xs:choice>

                  </xs:complexType>

               </xs:element>

            </xs:schema>

";

            return xsd;

        }

​

        public static DataSet GetDataSourceMappingTable()

        {

            DataSet dataSet = new DataSet();

            using (var reader = new StringReader(GetDataSetXsd()))

            {

                dataSet.ReadXmlSchema(reader);

            }

            for (int i = 0; i < 10; i++)

            {

                var row = dataSet.Tables["Table"].NewRow();

                row["SourceID"] = (i * 2).ToString();

                row["Caption"] = "Users_test" + (i == 7 ? "" : i.ToString());

                dataSet.Tables["Table"].Rows.Add(row);

            }

​

            // Add boundary condition rows

            dataSet.Tables["Table"].Rows.Add(dataSet.Tables["Table"].NewRow());

​

            var badRow = dataSet.Tables["Table"].NewRow();

            badRow["Caption"] = "MissingCaption";

            dataSet.Tables["Table"].Rows.Add(badRow);

​

            return dataSet;

        }

​

        public static void Test()

        {

            var ds = GetDataSourceMappingTable();

​

            {

                var DataSourceId = ds.Tables["Table"]

                    .Select("Caption = 'Users_test'") // Find rows with Caption = 'Users_test'

                    .Select(r => r["SourceID"])       // Project to the value of SourceId

                    .Where(s => s != DBNull.Value)    // Filter DBNull (might occur when the SourceID cell is missing

                    .Select(s => s.ToString())        // Project to string value

                    .SingleOrDefault();               // null if no matches, throw an exception if more than one match.

                Console.WriteLine(DataSourceId);

            }

​

            {

                var query = ds.Tables["Table"]

                    .Select("Caption = 'Users_test'") // Find rows with Caption = 'Users_test'

                    .Select(r => r["SourceID"])       // Project to the value of SourceId

                    .Where(s => s != DBNull.Value)    // Filter DBNull (might occur when the SourceID cell is missing

                    .Select(s => s.ToString());        // Project to string value

                foreach (var DataSourceId in query)

                {

                    Console.WriteLine("   " + DataSourceId);

                }

            }

​

            var MissingDataSourceId = ds.Tables["Table"]

                .Select("Caption = 'MissingCaption'")

                .Select(r => r["SourceID"])

                .Where(s => s != DBNull.Value)

                .Select(s => s.ToString())

                .SingleOrDefault();

            if (MissingDataSourceId != null)

            {

                Debug.Assert(MissingDataSourceId == null);

                throw new ArgumentNullException();

            }

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            TestClass.Test();

        }

    }