Rails ActiveRecord two fields each referencing the same table - ruby-on-rails

Question

I have a Player class that I want to have high_school_team and club_team properties. So then I figure Player will have high_school_team_id and club_team_id properties that point to the corresponding team. I try to do this in the following migration, but it doesn't work.
class CreatePlayers < ActiveRecord::Migration[6.0]
def change
create_table :players do |t|
t.string :first_name
t.string :middle_name
t.string :last_name
t.decimal :height
t.decimal :weight
t.date :birthday
t.references :team, :high_school_team, foreign_key: true
t.references :team, :club_team, foreign_key: true
t.decimal :gpa
t.string :class_year
t.string :intended_major
t.string :email
t.string :phone_number
t.text :notes
t.timestamps
end
end
end
It gives the following error:
code/scout-db [master●] » rails db:migrate
== 20191218003854 CreatePlayers: migrating ====================================
-- create_table(:players)
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:
you can't define an already defined column 'team_id'.
/Library/Ruby/Gems/2.6.0/gems/activerecord-6.0.2.1/lib/active_record/connection_adapters/abstract/schema_definitions.rb:372:in `column'
...
HighSchoolTeam and ClubTeam are models that do single table inheritance with Team.
I don't see why I'm getting the error. The docs seem to say that the first argument for t.referenes is table_name and the second ref_name. :team is the name of the table and I want the references to be high_school_team_id and club_team_id.
When I switch the order of the arguments to t.references, it still doesn't work. Somehow it gives the same error: you can't define an already defined column 'team_id'..

Answer 1

It looks you you are confusing SchemaStatement#add_reference and TableDefinition#references which have completely different signatures.
If you want to setup a foreign key column where the table can't be derived from the name of the column (the first argument) you just pass foreign_key: { to_table: :teams}.
class CreatePlayers < ActiveRecord::Migration[6.0]
def change
create_table :players do |t|
t.references :high_school_team, foreign_key: { to_table: :teams}
t.references :club_team, foreign_key: { to_table: :teams}
end
end
end
t.references :high_school_team, index: true as recommended by the other answers is NOT equivilent. That just adds a index to the column but no foreign key constraint.
You can then setup the assocations on Player as:
class Player < ApplicationRecord
belongs_to :high_school_team, class_name: 'Team'
belongs_to :club_team, class_name: 'Team'
end
You can't use a single has_many :players assocation on the other end though as the foreign key column can be either players.high_school_team_id or players.club_team_id.
class Team
has_many :high_school_team_players,
foreign_key: :high_school_team_id,
class_name: 'Player'
has_many :club_team_players,
foreign_key: :club_team_id,
class_name: 'Player'
end
But really a better alternative in the first place would have been to setup a join table:
class Player
has_many :placements
has_one :high_school_team,
through: :placements,
source: :team
class_name: 'Team'
has_one :club_team,
through: :placements,
source: :team
class_name: 'Team'
end
class Placement
belongs_to :player
belongs_to :team
end
class Team
has_many :placements
has_many :players, through: :placements
end

Answer 2

The doc you mentioned talks about the case when you need to add reference to an existing table.
For adding a refernence to a new table:
t.references :team, :high_school_team, foreign_key: true
This piece of code is wrong. Instead, it should be
t.references :high_school_team, foreign_key: {to_table: :teams}
to_table is needed to add database referential integrity
So your migration will be like this:
class CreatePlayers < ActiveRecord::Migration[6.0]
def change
create_table :players do |t|
....
t.references :high_school_team, foreign_key: {to_table: :teams}
t.references :club_team, foreign_key: {to_table: :teams}
....
end
end
end