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How do I improve these relationships (Rails Association question) ?

Ignacio Alonso asked in Databases

Im trying to make a project to practice more kinds of associations would you kindly help me understand this?

The basic idea is to have a betting game where one user generates a new bet that can only be accepted by another user (only 2 competitors assigned for each bet, the creator and the other player).

I’m thinking about 2 tables:

users

bets

Normally I would just have a one to many relationship for the user that created the bet. But I’m confused about the ‘competitor’ column where another user is also a user with a user_id. How can I express this relationship better than this:

After thinking it through it doesn’t look like a good setup because I’m renaming a column where I’m storing the user_id and having a many to many ‘through’ model doesn’t make sense since it is a “only one competitor can participate in that bet”.

I was thinking about a ‘one to one through’ creating a ‘competitors’ table like so:

Could you explain to me how to build it in a better way?

Many thanks!

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Your Bet model would have two belongs_to associations (one for the creator and one for the backer or however you'd like to call them):

class Bet < ApplicationRecord
  belongs_to :creator, class_name: 'User'
  belongs_to :backer, class_name: 'User'
end

Your bets table would need two columns for the user's id. With the above snippet, you would need a creator_id and a backer_id column.

And then if you wanted to access the bets from a user (created and backed bets for example) you would create two has_many associations on the User model:

class User < ApplicationRecord
  has_many :created_bets, foreign_key: 'creator_id', class_name: 'Bet'
  has_many :backed_bets, foreign_key: 'backer_id', class_name: 'Bet'
end

Hope that makes sense.

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