Rails 3.2.2 - has_many through

Question

trying to refactor code to provide clean association

A GAME has a HOME_TEAM and an AWAY_TEAM

A TEAM has many GAMES as a HOME_TEAM or an AWAY_TEAM

Association between GAME and TEAM is a straight-forward HABTM BUT I need to denote which of the two TEAMS associated with a GAME is the HOME_TEAM and which is the AWAY_TEAM. I did it by adding extra fields and associations but this is obvious very wet rather than dry. I know the answer is in through but I seem to have had a brain meltdown and can't quite get my head round this.

Basically I want to be able to do Game.teams (returns collection of both teams) and Game.home_team (get and set a TEAM to home_team) and Game.away_team (get and set a TEAM to away_team)

Sorry to pose such a straightforward sounding query but it's just got away from me

class Game < ActiveRecord::Base
  belongs_to :home_team
  belongs_to :away_team
  has_and_belongs_to_many :teams
end

class HomeTeam < ActiveRecord::Base
  belongs_to :team
  has_one :games
end

class AwayTeam < ActiveRecord::Base
  belongs_to :team
  has_one :games
end

class Team < ActiveRecord::Base
  has_and_belongs_to_many :games
  has_many :away_teams
  has_many :home_teams
end 

All help greatly appreciated

Peter

Answer 1

To do what you want to do, you should use a has_many :through instead of hatbm. See here for more info. In short, the good thing is that you can add other variables to the joins table. In your case, a boolean called home_team.

So here's what I'd do. First, create an association table (since I don't have much imagination, I'll call it participation):

create_table :participations, do |t|
  t.integer :game_id, :null => false
  t.integer :team_id, :null => false
  t.boolean :home_team
end

As you can see, unlike your gamesteams table, this one has an id. And you can add attributes to it. Then, I would use these models:

class Participation < ActiveRecord::Base
  belongs_to :game
  belongs_to :team
end

class Game < ActiveRecord::Base
  has_many :participations, :dependent => :destroy
  has_many :teams, :through => :participations
end

class Team < ActiveRecord::Base
  has_many :participations, :dependent => :destroy
  has_many :games, :through => :participations
end

So to get the teams of a game, you do @game.teams.

Now, to get home_team and away_team, add these methods to your Game model:

def home_team
  self.teams.joins(:participations).where("participations.home_team IS ?", true).first
end

def away_team
  self.teams.joins(:participations).where("participations.home_team IS ?", false).first
end

And then you'll be able to do @game.home_team and @game.away_team.

Peter's edit: Ok, so for mysql you'll have to use different where statements:

self.teams.joins(:participants).where("participants.home_team = ?", true).first self.teams.joins(:participants).where("participants.home_team IS NULL").first

I can either use " = ?", true and "!= ?", true --OR-- IS NOT NULL and IS NULL

I think for false you should try using where("participants.home_team = ?", false)

Ok, so so there are at least 2 ways to set up your teams.

1. You let the user pick which team is playing home
2. You assume the first team is the home team

If you go for number 1, you should use a radio button to let the user decide. Something like this:

<%= label_tag :home, 'Home Team' %><br />
<%= label_tag :home_team_1, 'Team 1' %><%= radio_button_tag :home_team, 1 %>
<%= label_tag :home_team_2, 'Team 2' %><%= radio_button_tag :home_team, 2 %>

So if params[:home_team] == 1, the first team is the home team, if params[:home_team] == 2, the second team is the home team.

If you go for number 2, then, you should have something like this in your form do add the teams to your game:

  <%= label_tag :name, 'Home Team' %>
  <%= text_field_tag :name, nil, :name => "home[]" %>

  <%= label_tag :name, 'Away Team' %>
  <%= text_field_tag :name, nil, :name => "away[]" %>

So then in your controller you can do something like

@game = Game.new(params[:game])

home = Team.create(params[:home])
# or
home = Team.find_or_create_by_name(params[:home][:name])
@game.participations.create(:team_id => home.id, :home_team => true or 1)

away = Team.find_or_create_by_name(params[:away][:name])
@game.participations.create(:team_id => away.id, :home_team => false or 0)