"Is it all one piece?"
Why would it be one piece? As if I am so fashionably challenged that I could not put together an outfit on my own? Do I need to rely on Daisy Fuentes or some other Kohl's spokes model to have some overseas seamstress put a half shirt (DICKIE!) inside a sweater vest to make it easier for me?
No - everyone, it is not one piece, and it never will be.