php - Retrieve specific information from a form - Symfony2 -

i want know how obtain specific data form sent user. is, when user submits form, example want save data in table, , other in table. help, sorry inconvenience

for data (what think don't need, comprehension):

 $data = $form->getdata(); 

for specific fields, e.g. username (what need):

 $username = $form["username"]->getdata();