Access multiple databases from winforms without adding datasource

If all the databases have the exact same tables and columns and you are using TableAdapter try the following out.

Caveat It appears the following will not work when changing the connection string after the form has loaded. If you were to change it in a main form than open a child form the connection string works but not when changing the connection string in the same form as the TableAdapter. Best guess is connection string is set when the form initializes thus does not see the changed connection string.

Usage

var source = Path.Combine(ConnectionHelper.BasePath, "Database1.accdb");
ConnectionHelper.ChangeConnection(source,2);

Change BasePath to match your path to the databases.

using System.Configuration;
using System.Data.OleDb;
using System.IO;
using static System.Configuration.ConfigurationManager;

namespace AccessMultiConnections.Classes
{
    public class ConnectionHelper
    {
        /// <summary>
        /// Location of all databases
        /// </summary>
        public static string BasePath = 
            "C:\\Dotnetland\\Databases";

        /// <summary>
        /// Change database connection by index in connection string section
        /// </summary>
        /// <param name="source">Path and database name</param>
        /// <param name="index">ordinal index of connection string</param>
        /// <remarks>
        /// Can change index parameter to a string name representing the connection
        /// string if desire.
        /// </remarks>
        public static void ChangeConnection(string source, int index)
        {
            var config = OpenExeConfiguration(ConfigurationUserLevel.None);
            var connectionStringsSection = (ConnectionStringsSection)config
                .GetSection("connectionStrings");

            // in this case the index to the connection string is 2
            var current = connectionStringsSection.ConnectionStrings[index]
                .ConnectionString;

            var builder = new OleDbConnectionStringBuilder(current)
            {
                DataSource = source
            };

            connectionStringsSection.ConnectionStrings[index].ConnectionString = 
                builder.ConnectionString;

            config.Save();

            RefreshSection("connectionStrings");
            Properties.Settings.Default.Reload();

        }

        /// <summary>
        /// Provides the current database name without a path in appsettings.config
        /// </summary>
        /// <returns>File name for current connection</returns>
        public static string CurrentConnectionString()
        {
            var config = OpenExeConfiguration(ConfigurationUserLevel.None);
            var connectionStringsSection = (ConnectionStringsSection)config
                .GetSection("connectionStrings");

            var builder = 
                new OleDbConnectionStringBuilder(
                    connectionStringsSection.ConnectionStrings[2]
                        .ConnectionString);

            return Path.GetFileName(builder.DataSource);
        }
    }
}

Edit - noticed I hard coded the connection string in CurrentConnectionString, here is the proper code.

/// <summary>
/// Provides the current database name without a path in appsettings.config
/// </summary>
/// <param name="index">ordinal index of connection string</param>
/// <returns>File name for current connection</returns>
public static string CurrentConnectionString(int index = 2)
{
    var config = OpenExeConfiguration(ConfigurationUserLevel.None);
    var connectionStringsSection = (ConnectionStringsSection)config
        .GetSection("connectionStrings");

    var builder = 
        new OleDbConnectionStringBuilder(
            connectionStringsSection.ConnectionStrings[index]
                .ConnectionString);

    return Path.GetFileName(builder.DataSource);
}