Rails pattern to build new object related to current view/model

Rails newb question: Say I'm currently viewing the show.html for one of my classes(Dog). This class has_many Flea(s). If I put a "add new flea" link that links to new_flea_path (/fleas/new) when clicked it will build a new Flea (`@flea = Flea.new) and render flea's new.html.haml with its form fields...

But, how/where do I automatically pass in the dog_id that the flea needs to referen开发者_运维问答ce?

is this a routes issue? maybe /dog/3/flea/new is what I need to handle in routes? or is this a controller thing?

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What you are looking for is referred to as "Nested Resources". you can read up on them here