using System;

using System.Text;

using System.Collections.Generic;

using Npgsql;

using NpgsqlTypes;

public class Program

{

    /*

    populated during startup from the DB

    each table has a name (dict key) and a list of columns with a (name, type) tuple

    */

    private static Dictionary<string,List<(string, string)>> _tables;

    public static void Main()

    {

        //suppose this is are the values to be imported

        var data = new string[7][13];

        var tableName = "my_table";

        var columns = new List<(string name, string type)> (_tables[tableName]);

        var sb = new StringBuilder();

        sb.Append("INSERT INTO ");

        sb.Append(tableName);

        sb.Append(" (");

        foreach(var column in columns)

        {

            sb.Append(column.name);

            sb.Append(", ");

        }

        sb.Length = sb.Length - 2;

        sb.Append(") VALUES (");

        for(var i=0; i<columns.Count; i++)

        {

            var p = "@p" + Convert.ToString(i);

            sb.Append(p);

            if(i<columns.Count-1)

                sb.Append(", ");

        }

        sb.Append(")");

        var stmt = sb.ToString();

        using (var conn = new NpgsqlConnection("conn string"))

        using (var cmd = new NpgsqlCommand(stmt, conn))

               {

                   for (var i=0; i<columns.Count; i++)

                   {

                       var p = "@p" + Convert.ToString(i);

                       cmd.Parameters.Add(_createPara(p, columns[i].type));

                   }

                    cmd.Prepare();

                    for (var r=0; r<data.Length; r++)

                    {

                        var row = data[r];

                        for (var c=0; c<row.Length; c++)

                        {

                            cmd.Parameters[c].TypedValue = // could a helper method return the correct type?

                        }

                        cmd.ExecuteNonQuery();

                    }

               }

​

    }

    private static NpgsqlParameter _createPara(string paraName, string typeName)

    {

        switch (typeName)

        {

            case "char":

                return new NpgsqlParameter<string>(paraName, NpgsqlDbType.Text);

            case "float":

                return new NpgsqlParameter<float>(paraName, NpgsqlDbType.Real);

            case "numeric":

                return new NpgsqlParameter<decimal>(paraName, NpgsqlDbType.Numeric);

        }

    }

}