web-dev-qa-db-fra.com

Rails se joint via l'association

Dans Ruby on Rails, je veux trouver des employeurs dans la ville. Disons que les modèles sont configurés de cette façon:

City
has_many :suburbs
has_many :households, :through => suburbs
has_many :people, :through => suburbs

Suburb
has_many :households
has_many people, :through => households
belongs_to :city


Household
has_many :people
belongs_to :suburb

People
belongs_to :household
belongs_to :employer


Employer
has_many :people

J'ai l'impression que je veux qu'une sorte d'employeur rejoigne some_city.people mais je ne sais pas comment faire. Si les gens appartenaient directement aux villes, je pourrais rejoindre Employeur aux gens où city_id est quelque chose, mais je veux trouver les mêmes données sans cette jointure directe et je suis un peu perdu.

Je vous remercie.

sqlruby-on-railsruby-on-rails-3joinruby-on-rails-3.2
30
spitfire109

Vous pouvez faire la jointure comme l'illustre jvans. Ou vous pouvez configurer vos relations comme suit:

class Employer < ActiveRecord::Base
  has_many :people
  has_many :households, through: :people
  has_many :suburbs, through: :households
  has_many :cities, through: :suburbs
end

class Person < ActiveRecord::Base
  belongs_to :household
  belongs_to :employer
end


class Household < ActiveRecord::Base
  belongs_to :suburb
  has_many :people
end

class Suburb < ActiveRecord::Base
  belongs_to :city
  has_many :households
  has_many :people, through: :households
end

class City < ActiveRecord::Base
  has_many :suburbs
  has_many :households, through: :suburbs
  has_many :people, through: :households
  has_many :employers, through: :people
end

Ensuite, vous pouvez joindre City à partir de Employer, et vice-versa, directement.

Par exemple:

Employer.joins(:cities).where("cities.name = ?", "Houston").first

SELECT "employers".* FROM "employers" 
INNER JOIN "people" ON "people"."employer_id" = "employers"."id" 
INNER JOIN "households" ON "households"."id" = "people"."household_id" 
INNER JOIN "suburbs" ON "suburbs"."id" = "households"."suburb_id" 
INNER JOIN "cities" ON "cities"."id" = "suburbs"."city_id" WHERE (cities.name = 'Houston') 
LIMIT 1
19
Sean Hill

Utiliser des jointures imbriquées

Employer.joins({:people => {:household => {:suburb => :city}}})

devrait vous donner la table de jointure que vous recherchez. Si vous traversiez l'autre direction, vous utiliseriez des noms pluriels

City.joins( :suburbs => {:households => {:people => :employers }})
42
jvans