Active Record Association after ".where" query - ruby

Question

I've got three models: Decks, Slots and Cards. I put them together like so...
Decks are made of many slots, each slot contains one card and any one card can show up in a number of different slots.
I modeled it after the "Order - Order Line Item - Product" structure, hope that makes sense.
Anyways, Decks have an integer field called :deck_type, and suppose I want to get all of the decks of a certain type and then see all of their cards. I EXPECT to be able to run this query but I get an error of undefined method 'cards':
Deck.where(:deck_type => 1).cards
To get all decks of type 1 and then spit out their cards. I have an association established of "deck has many cards through slots", and when I call ".cards" on a single deck it works fine to return the cards.
I feel like this should be a pretty basic query - what am I missing?
Thanks in advance for any insight.

Answer 1

The method cards is for one deck only. So the following should work:
Deck.where(deck_type: 1).first.cards
The first will fetch 1 deck.
If you want cards that belong to decks with deck_type 1, then you've got a few options:
Deck.where(deck_type: 1).map(&:cards).flatten.uniq
That will apply the cards method on each found deck and then get all cards. The flatten will make the results into a 1D array and then uniq will ensure that no duplicates are present, if any.
But the following might be faster:
deck_ids = Deck.where(deck_type: 1).pluck(:id)
Card.where(deck_id: deck_ids)
I think it's safe to assume your Card model has a deck_id attribute. From the above, you will fetch only those cards that have deck_id in the deck_ids variable.
Even better however would be the following as it'll be a single database query. Assuming you've got the right associations setup, you can do:
# replace 'decks' with Deck.table_name if necessary
Card.joins(:deck).where(decks: {deck_type: 1})
I hope that last one is self-explanatory.