Rails: is it possible to add extra attribute to a has_and_belongs_to_many association?

Question

What I mean is if I have two models, connected by a has_and_belongs_to_many association, can I store other data in the join table for each association? That is, the extra data w

Answer 1

Actually, this is possible.

1) Add a quantity key to the packages_parts join table

2) Add this to your Part model

has_and_belongs_to_many :packages, -> { select("packages.*, 
packages_parts.quantity") }

Now you can do part.packages[0].quantity, for example.

What this does is tell Rails to fetch the quantity key whenever it gets the packages for a specific part.

(You can do the same for your Package model if you want to do package.parts.first.quantity as well - just put this on the Package model also, replacing 'packages' with 'parts')

More info: https://ducktypelabs.com/using-scope-with-associations/