Best way to implement has_n

Question

How would you implement a has_n association on Rails for a given n? Let's say for example a rugby team. It has 15 players. Would you implement it as has_many and check in before save to make sure it has 15 players, or would you prefer to implement it as 15 belongs_to? Note that the order is important in this case.

I think your question is directly related to this [question](http://stackoverflow.com/q/4836897/22371). — kafuchau, May 15 '12 at 03:17
I don't think it's directly related. That question uses a join table. No need for that here. — Mark Paine, May 15 '12 at 04:12

Mark Paine · Accepted Answer · 2012-05-16T14:51:16.930

1

Edited to reflect your request for ordering...

You'll need to add a sort_key to the players table. You can use an integer, but a float is always a more flexible choice. Then use the :order => "sort_key" phrase.

class Team < ActiveRecord::Base
  has_many :players, :order => "sort_key", :inverse_of => :team
end

class Player < ActiveRecord::Base
  belongs_to :team, :inverse_of => :players

  validate :validate_players_count, :on => :create
  def validate_players_count
    if team.players.size > 15
      errors[:base] << "a team can only have 15 players"
    end
  end
end

edited May 16 '12 at 14:51

answered May 15 '12 at 04:12

Mark Paine

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Then how would you change the player on the first position to the one in the forth? – fotanus May 16 '12 at 14:41
Edited my answer to reflect the ordering request. – Mark Paine May 16 '12 at 14:53
Thanks, that is what I needed. Now to change two players from positions all I have to do is update the sort key. – fotanus May 16 '12 at 19:19

score 0 · Answer 2 · edited May 15 '12 at 22:13

0

I prefer to make it by has_many and validate players quantity when adding a new player.

I think that is the right way to make one-to-many relation.

edited May 15 '12 at 22:13

RThomas

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answered May 15 '12 at 03:41

vfedorov_ru

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Best way to implement has_n

2 Answers2