C#

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <sectionGroup name="common">
      <section name="logging" type="Common.Logging.ConfigurationSectionHandler, Common.Logging" />
    </sectionGroup>
  </configSections>
  <nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <targets>
     </targets>
    <rules>
    </rules>
  </nlog>


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Common.Logging;
using sample;
using System.Configuration;
using System.Xml.Linq;  
using NLog;

namespace sample
{
    public class Etest
    {
        private static Logger logger = LogManager.GetCurrentClassLogger(); 
        private static ILog log = LogManager.GetCurrentClassLogger();
}
}

1. The following code is from the app.config file:
<connectionStrings>
    
    <add name="esample.Properties.Settings.devtestConnectionString"
      connectionString="Data Source=dev;Initial Catalog=devtest;Integrated Security=True"
      providerName="System.Data.SqlClient" />    
  </connectionStrings>

2. The following is from the settings.settings file
<?xml version='1.0' encoding='utf-8'?>
<SettingsFile xmlns="http://schemas.microsoft.com/VisualStudio/2004/01/settings" CurrentProfile="(Default)" GeneratedClassNamespace="esample.Properties" GeneratedClassName="Settings">
  <Profiles />
  <Settings>
    <Setting Name="devtestConnectionString" Type="(Connection string)" Scope="Application">
      <DesignTimeValue Profile="(Default)"><?xml version="1.0" encoding="utf-16"?>
<SerializableConnectionString xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <ConnectionString>Data Source=dev;Initial Catalog=devtest;Integrated Security=True</ConnectionString>
  <ProviderName>System.Data.SqlClient</ProviderName>
</SerializableConnectionString></DesignTimeValue>
      <Value Profile="(Default)">Data Source=dev;Initial Catalog=devtest;Integrated Security=True</Value>
    </Setting>
   </Settings>
</SettingsFile>

The following is from the settings.designer.cs file
namespace esample.Properties {
    
    
    [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.VisualStudio.Editors.SettingsDesigner.SettingsSingleFileGenerator", "9.0.0.0")]
    internal sealed partial class Settings : global::System.Configuration.ApplicationSettingsBase {
        
        private static Settings defaultInstance = ((Settings)(global::System.Configuration.ApplicationSettingsBase.Synchronized(new Settings())));
        
        public static Settings Default {
            get {
                return defaultInstance;
            }
        }
        
        [global::System.Configuration.ApplicationScopedSettingAttribute()]
        [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
        [global::System.Configuration.SpecialSettingAttribute(global::System.Configuration.SpecialSetting.ConnectionString)]
        [global::System.Configuration.DefaultSettingValueAttribute("Data Source=dev;Initial Catalog=devtest;Integrated Security=True")]
        public string devtestConnectionString {
            get {
                return ((string)(this["devtestConnectionString"]));
            }
        }
        
        
    }
}

The following is from the *.designer.cs

namespace esample
{
	using System.Data.Linq;
	using System.Data.Linq.Mapping;
	using System.Data;
	using System.Collections.Generic;
	using System.Reflection;
	using System.Linq;
	using System.Linq.Expressions;
	using System.ComponentModel;
	using System;
        using System.Configuration;
	
	
	[System.Data.Linq.Mapping.DatabaseAttribute(Name="devtest")]
	public partial class esampleDataContext : System.Data.Linq.DataContext
	{
		
		private static System.Data.Linq.Mapping.MappingSource mappingSource = new AttributeMappingSource();

		
		public esampleDataContext() :

        base(global::esample.Properties.Settings.Default.devtestConnectionString, mappingSource)
        //base(ConfigurationManager.ConnectionStrings["esample.Properties.Settings.devtestConnectionString"].ConnectionString,  mappingSource)
          {	
			OnCreated();
		}
		
		public esampleDataContext(string connection) : 
				base(connection, mappingSource)
		{
			OnCreated();
		}