Route binding. http://laravel.com/docs/routing#route-model-binding

Routes.php

Route::get('/view/{post_slug}', ['uses' => 'PostController@view']);

Route::bind('post_slug', function($value, $route)
{
    // Return a model based on the value in the route URI
    return Post::where('slug', $value)->firstOrFail();
});

PostController.php

function view(Post $post)
{
    // $post is an instance of Post that is returned from the Route::bind() method.
    return View::make('posts.view', ['post' => $post]);
}

I get this error

No query results for model [User]

// Routes
Route::get('post/{slug}, 'PostsController@show');

// PostsController
public function show($slug)
{
    $post = Post::whereSlug($slug)->first();

    return View::make('posts.show', ['post' => $post]);
}