Hi,
I have a many to many association in which the join table has
additional columns. I'm modeling a deck management application for
Magic the Gathering, and I have the following tables:
DB.create_table(:mtg_database) do
Integer :gatherer_id
primary_key [:gatherer_id]
String :name
String :cost
String :spell_type
String :power_toughness
String :rules
String :sets
end
DB.create_table(:deck) do
primary_key :id
String :name
String :format
String :description
end
DB.create_table(:deck_card) do
foreign_key :deck_id, :deck
foreign_key :gatherer_id, :mtg_database
primary_key [:deck_id, :gatherer_id]
Integer :qty
end
The deck_card table contains the relation between a deck and the cards
it contains. For each deck and card, it has an additional column named
qty which contains the number of such card a deck has. What I would
like to do is have a method in a deck model that allows me to add a
card to a deck, which will handle the qty field correctly (set it to 1
the first time a card is added to a deck, increment it from that point
on). I have managed to make it work, checking an old message from this
list related to books and locations, as so:
class Card < Sequel::Model(:mtg_database)
unrestrict_primary_key
one_to_many :deck_card
end
class DeckCard < Sequel::Model(:deck_card)
many_to_one :card, :key => :gatherer_id
many_to_one :deck
end
class Deck < Sequel::Model(:deck)
many_to_many :cards, :join_table=>:deck_card, :right_key =>
:gatherer_id, :order=> :name
one_to_many :deck_card
def deck_card(card)
deck_card_dataset[:gatherer_id => card.gatherer_id]
end
def add_card_to_deck card
deck_card = deck_card card
if deck_card
deck_card.update({:qty => deck_card.qty + 1})
else
DeckCard.create({:card => card, :deck => self, :qty => 1})
end
end
end
This works and I'm able to add cards to decks like this:
deck = Deck.first(:id => some_id)
deck.add_card_to_deck(Card.first(:gatherer_id => some_card_id))
But I have some questions:
1.- Is this the best way to handle this?
2.- I would now need a way to iterate through all the deck's cards
having access to both the card info (all columns in mtg_database
table) along with the qty column from the join table. What would be
the best way to do that?
3.- I had to add the unrestrict_primary_key in the Card model. Until I
did, I wasn't able to create cards setting the gatherer_id, which is
an external id that I want to have as pk of that table. Am I doing
something wrong? I'm creating Cards like this:
def update_or_create_card params
card = Card.first :gatherer_id => params[:gatherer_id]
card = Card.new unless card
card.gatherer_id = params[:gatherer_id]
card.name = params[:name]
card.cost = params[:cost]
card.spell_type = params[:type]
card.power_toughness = params[:power_toughness]
card.rules = params[:rules]
card.sets = params[:sets]
card.save
card
end
Regards,
Jesus.
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