DataRetriever.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Npgsql;
using System.Data;
using Dapper;

namespace Conexion
{
    public class DataRetriever : IDisposable
    {
        private String connectionString = "Server=;Port=;User ID=;Password=;Database ;";
        private NpgsqlConnection dbConnection;

        public DataRetriever()
        {
            dbConnection = new NpgsqlConnection(connectionString);
            dbConnection.Open();
        }

        public IEnumerable<Ciudad> GetCiudades()
        {
            return dbConnection.Query<Ciudad>("select * from ciudad");
        }

        public void Dispose()
        {
            dbConnection.Close();
        }


    }
}

Data Retriever Class with Dapper and PostgreSQL