Sending json to symfony controller

As Marek noticed:

$this->getRequest()

already returns the request object, you're accessing the request property of the request, that doesn't add up. Either try:

$data = $this->request->get('json');

Or use:

$data = $this->getRequest()->get('json');

You can, of course assign the return value of $this->getRequest() to a variable, and call the get method on that var from there on end... anyway, here's my initial answer, it does contain some more tips, and considerations you may find useful:

You should be able to get the data this way, though AJAX requests + echoing in a template? That does sound a bit strange. I don't see you passing the $data variable to a $this->render call anywhere.

This is a copy-paste bit from a controller action in one of my projects. It works just fine there:

public function indexAction()
{
    if (!$this->getRequest()->isXmlHttpRequest())
    {//check if request is AJAX request, if not redirect
        return $this->redirect(
            $this->generateUrl('foo_bar_homepage')//changed this, of course
        );
    }
    $id = $this->getRequest()->get('id',false);//works fine

However, I can't begin to grasp why you're doing this:

 var data = '{"firstname":"John"}';

Why not simply go for:

$.ajax({
    type: "POST",
    url: url,//post how you get this URL please...
    data: {firstname: 'John'},//jQ will sort this out for you
    success: function(response)
    {
        console.log(response);
    }
    error: function()
    {
        console.log('an error occured');
        console.log(arguments);//get debugging!
    }
});

Then, in your controller you're able to:

$this->getRequest()->get('firstname');//it should be John

You could even pass {json:{firstname: 'john'}} as the data param to $.ajax, the only difference in your controller will be, that you have to do this:

$data = $this->getRequest()->get('json');
$firstName = $data['firstname'];

That should work just fine, unless there's somthing you're not telling us :)

RECAP:
This is what I'd write:

public function createAction()
{//no Request param in controller
    if (!$this->getRequest()->isXmlHttpRequest())
    {//no ajax request, no play...
        $this->redirect(
            $this->generateUrl('homepage_route')
        );
    }
    $data = $this->getRequest()->get('firstname');
    //return json response:
    return new Response(json_encode(array('dataReceived' => $data));
    //return rendered HTML page:
    return $this->render('MyBundle:Counter:test.html.twig', array(
        'data' => $data          
    ));
}

Of course, then the JS code should read:

$.ajax({  
    type: "POST",  
    url: 'route/to/create'
    data: {firstname:'John'},
    success: function(response)
    {
        console.log(response);
    }
});

I have tested this, and I see no reason why this shouldn't work. It works just fine for me...

Please note this was @EliasVanOotegem original example but there are some obvious steps missing

in the controller i'm reading a few replies as in "I cannot see how this works as i'm getting null" this is because your not correctly keying your object.

i.e.

var data = { name : 'john' };

$.ajax({
  type: "POST",
  url: url,//post how you get this URL please...
  data: {json : data},//jQ will sort this out for you
  success: function(response)
  {
      console.log(response);
  }
  error: function()
  {
    console.log('an error occured');
    console.log(arguments);//get debugging!
  }
});

as you can now see accessing the requerst object like

$request->get('json');

refers to the post key for the json data

Is the content what you're trying to retrieve, neither params nor headers.

Try:

$request->getContent();

In your case $request->request->get('json') should do.