1. Interface

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DataBase.Interface
{
    

    //  database   Interface 
    public interface IDBInterface
    {
    
        //  Query methods 
        void Query();
    }
}

2.SQL database （ Class library DataBase.Sql.dll）

using DataBase.Interface;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DataBase.Sql
{
    
    // SQl class 
    public class SqlServerHelper : IDBInterface
    {
    
        public SqlServerHelper()
        {
    
            Console.WriteLine($"{
      this.GetType().Name}  Constructed ");
        }

        //  Interface inheritance 
        public void Query()
        {
    
            Console.WriteLine($"{
      this.GetType().Name}.Query");
        }
    }
}

3.Mysql database （DataBase.Mysql.dll）

using DataBase.Interface;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DataBase.Mysql
{
    
    // Mysql  database  
    public class MySqlHelper : IDBInterface
    {
    
        //  Constructors 
        public MySqlHelper()
        {
    
            Console.WriteLine($"{
      this.GetType().Name}  Constructed ");
        }

        //  Inquire about 
        public void Query()
        {
    
            Console.WriteLine($"{
      this.GetType().Name}.Query");
        }
    }
}

4. Factory （ Read configuration file ）

The configuration file

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2" />
    </startup>
	<appSettings>
		<add key="IDBHelperConfig" value="DataBase.Sql.SqlServerHelper, DataBase.Sql"/>
	</appSettings>
</configuration>

using DataBase.Interface;
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace ReflectionFactory
{
    
    public class Factory
    {
    
        //  Read configuration file 
        public static string IDBHelperConfig = ConfigurationManager.AppSettings["IDBHelperConfig"];

        // Dll  file name 
        private static string DllName = IDBHelperConfig.Split(',')[1];

        //  Reflection   Class name 
        private static string TypeName = IDBHelperConfig.Split(',')[0];

        //  Factory creation function 
        public static IDBInterface CreateHelper()
        {
    
            Console.WriteLine(" load DLL:" + DllName);
            //  Reflection loading Dll Assembly 
            Assembly assembly = Assembly.Load(DllName);

            Console.WriteLine($" Get class : {
      TypeName}");

            //  Get the  Type
            Type typeHelper = assembly.GetType(TypeName);

            //  Create objects 
            object oHelper = Activator.CreateInstance(typeHelper);

            //  Type conversion to   Interface type 
            IDBInterface iDbHelper = (IDBInterface)oHelper;
            return iDbHelper;
        }
    }
}

5. Call tests

using DataBase.Interface;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ReflectionFactory
{
    
    class Program
    {
    
        static void Main(string[] args)
        {
    
            #region  Reflection and factory mode 
            Console.WriteLine("----- Reflection and factory mode ----------");

            //  Created using the factory pattern   object （ Interface ）
            IDBInterface iDBInterface = Factory.CreateHelper();

            Console.WriteLine("----- Call the object function ----------");
            //  Call the object function 
            iDBInterface.Query();

            #endregion
            Console.ReadLine();
        }
    }
}

result

SQL

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2" />
    </startup>
	<appSettings>
		<add key="IDBHelperConfig" value="DataBase.Sql.SqlServerHelper, DataBase.Sql"/>
	</appSettings>
</configuration>

Mysql

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2" />
    </startup>
	<appSettings>
		<add key="IDBHelperConfig" value="DataBase.Mysql.MySqlHelper, DataBase.Mysql"/>
	</appSettings>
</configuration>