SYMFONY2 How to add tags and categories in posts

I have a problem with Symfony2. I want add to posts in database tag name and category name but I can't :/ I have table 'tag' and 'category' in database. I reads tags and cat from database and display option for user(checkbox fields). When I check more than one position in database I have one position. How to do it?

Here is a picture that shows what I want to do: http://ift.tt/1DMulEC

Regards, Tomasz Bęben