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Asked: 2026-05-10T18:32:30+00:00

I’m building an app in Ruby on Rails, and I’m including 3 of my

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I’m building an app in Ruby on Rails, and I’m including 3 of my models (and their migration scripts) to show what I’m trying to do, and what isn’t working. Here’s the rundown: I have users in my application that belong to teams, and each team can have multiple coaches. I want to be able to pull a list of the coaches that are applicable to a user.

For instance, User A could belong to teams T1 and T2. Teams T1 and T2 could have four different coaches each, and one coach in common. I’d like to be able to pull the list of coaches by simply saying: 

u = User.find(1) coaches = u.coaches

Here are my migration scripts, and the associations in my models. Am I doing something incorrectly in my design? Are my associations correct?

class CreateUsers < ActiveRecord::Migration   def self.up     create_table :users do |t|       t.column :login, :string, :default => nil       t.column :firstname, :string, :default => nil       t.column :lastname, :string, :default => nil       t.column :password, :string, :default => nil       t.column :security_token, :string, :default => nil       t.column :token_expires, :datetime, :default => nil       t.column :legacy_password, :string, :default => nil     end   end    def self.down     drop_table :users   end end  class CreateTeams < ActiveRecord::Migration   def self.up     create_table :teams do |t|       t.column :name, :string     end   end    def self.down     drop_table :teams   end end  class TeamsUsers < ActiveRecord::Migration   def self.up     create_table :teams_users, :id => false do |t|       t.column :team_id, :integer       t.column :user_id, :integer       t.column :joined_date, :datetime     end   end    def self.down     drop_table :teams_users   end end

Here are the models (not the entire file):

class User < ActiveRecord::Base    has_and_belongs_to_many :teams   has_many :coaches, :through => :teams  class Team < ActiveRecord::Base   has_many :coaches   has_and_belongs_to_many :users  class Coach < ActiveRecord::Base   belongs_to :teams end

This is what happens when I try to pull the coaches:

u = User.find(1) => #<User id: 1, firstname: 'Dan', lastname: 'Wolchonok'> >> u.coaches ActiveRecord::StatementInvalid: Mysql::Error: #42S22Unknown column 'teams.user_id' in 'where clause': SELECT `coaches`.* FROM `coaches`    INNER JOIN teams ON coaches.team_id = teams.id    WHERE ((`teams`.user_id = 1))

Here’s the error in sql:

Mysql::Error: #42S22Unknown column ‘teams.user_id’ in ‘where clause’: SELECT coaches.* FROM coaches INNER JOIN teams ON coaches.team_id = teams.id WHERE ((teams.user_id = 1))

Am I missing something in my :through clause? Is my design totally off? Can someone point me in the right direction?

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1 Answer

  1. You can’t do a has_many :through twice in a row. It’ll tell you that its an invalid association. If you don’t want to add finder_sql like above, you can add a method that mimics what you’re trying to do.

      def coaches     self.teams.collect do |team|       team.coaches     end.flatten.uniq   end
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