Is there a cheat to fill up all of your national pokedex in Pokemon diamond?

Take you,er game boy game and put it in D.S and go to the menu then go to migrate from what ever the the name of the game is then pick 6 Pokemon then go to pale park to go is go south of sandgym town and go through water an yill see a building and go in and talk to a man and heil let you pass and go to long grass and water and catch all 6 Pokemon and when you,er done heil call you back in and let you keep all 6 Pokemon and that's how to cheat to get the national pokedex.