Rails: How do I map out this has_many, has_many association? - sql

Question

I'm currently working on a game for a student project. I'm spinning in circles engineering the associations. Any guidance from the community would be greatly appreciated.
There are 3 models/classes: Games, Characters and Quotes.
Game:
has_many Characters (two historical characters with a bank of quotes, you will have to choose who said the quote)
has_many Quotes (through games)
Character:
has_many Games (to keep track of games a character has appeared in)
has_many Quotes
Quote:
belongs_to Character
class Game < ActiveRecord::Base
has_many :characters
# Each game will have exactly 2 characters
# #game.characters will return the two characters
has_many :quotes, through: :characters
end
class Characters < ActiveRecord::Base
has_many :games
# #character.games will return all games the character appeared in
has_many :quotes
end
class Quote < ActiveRecord::Base
belongs_to :character
end
These are the migrations I've created:
class CreateGames < ActiveRecord::Migration[5.1]
def change
create_table :games do |t|
t.text :game_state
end
end
end
class CreateCharacters < ActiveRecord::Migration[5.1]
def change
create_table :characters do |t|
t.string :name
t.string :title
end
end
end
class CreateQuotes < ActiveRecord::Migration[5.1]
def change
create_table :quotes do |t|
t.string :content
t.belongs_to :character, index: true
end
end
end
Goals:
instantiate a new game with two characters: #game =
Game.new(#character1, #character2)
#game.characters should return
the two characters.
#character1.games should return all games
the character appeared in.
#game.quotes should return all the
quotes from the two characters.
My first instinct is that I need a join table for the has_many has_many relationship and to keep track of the games. For example:.
class GamesPlayed < ApplicationRecord
belongs_to :character1
belongs_to :character2
belongs_to :game
end
Thanks in advance if you can offer me any guidance or suggestions.

Answer 1

The way you've written your associations, you haven't really fleshed out the many to many association between the Game & Character models. Basically you'll need a join table for that.
In it's simplest form, it will look something like:
class Game < ActiveRecord::Base
has_many :game_character_joins
has_many :characters, through: :game_character_joins
end
class Characters < ActiveRecord::Base
has_many :game_character_joins
has_many :games, through: :game_character_joins
end
class GameCharacterJoin < ActiveRecord::Base
belongs_to :game
belongs_to :character
end
The migrations for the join table would be:
class CreateGameCharacterJoin < ActiveRecord::Migration[5.1]
def change
create_table :game_character_joins do |t|
t.integer :game_id
t.integer :character_id
end
end
end
That's really the easier part of what I think you're asking.
Then, the association between Quote and Game is kind of odd looking to me. Is this because you need to get all the Quotes for a single Game? There are a lot of ways to model that--is the idea of an association between Quote and Game a matter of convenience? It seems to me that a quote is
requires both a character and a game,
owned by a character
is about a game
How you approach this really becomes a matter of preference. Depending on the importance of the associations, you can have a many to many between character & quote and another between game & quote, or you can just rely on additional data in the quote table to specify which game it's about.

Answer 2

To model a many-to-many relationship you can use either a has_and_belongs_to_many which would rely on a join table (no model), or a model that represents the relationship between the two models.
I wonder if you don't really have a many-to-many relationship though. Consider this instead:
class Game
belongs_to :player_one, class_name: 'Player'
belongs_to :player_two, class_name: 'Player'
scope :for_player, ->(player) { where(player_one: player).or(where(player_two: player)) }
def players
Player.where(id: [player_one_id, player_two_id])
end
end
class Player
def games
Game.for_player(self)
end
end
# In use:
#game = Game.find(1)
#game.players
#player = Player.find(1)
#player.games
#player.games.where(created_at: 1.week.ago..Date.today)
Note that both game.players and player.games return an ActiveRecord_Relation that you can use in additional scopes, you just don't have a has_many on the Player model.