How to redisplay a form with previous values when validation fails?

Question

I have a form, which has to be passed by some other validations than unusual (about 4 fields are depending from each other). Thing is, when its failed, I redirect the user back, but then the form loses its values, I dont want it. I know it can be done with session, but there might be a "sanitier" way. Code is usual:

public function printAction()
{
    if ($this->getRequest()->getMethod() == "POST")
    {
        $form->bindRequest($this->getRequest());
        if ($form->isValid())
        {
             .... more validation.... Failed!
             return $this->redirect($this->generateUrl("SiteHomePeltexStockStockHistory_print"));
             // and this is when I lose the values.... I dont want it
        }
    }
}

Answer 1

You can use the same action for both GET and POST requests related to a form. If validation fails, just don't redirect and the same form will be redisplayed with entered values and validation error messages:

/**
 * @Template
 */
public function addAction(Request $request)
{
    $form = /* ... */;        

    if ($request->isMethod('POST')) {
        $form->bind($request);

        if ($form->isValid()) {
            // do something and redirect
        }

        // the form is not valid, so do nothing and the form will be redisplayed
    }

    return [
        'form' => $form->createView(),
    ];
}