Rails 4 + Postgresql - 以 2 个条件连接表

Question

我需要列出Inputs 有Translations 和language_id = 1 并且没有language_id = 2 的翻译

我目前的范围是：

scope :language, -> (id){joins(:translations).where('translations.language_id = 1)}

型号：

class Input < ActiveRecord::Base
  has_many :translations
  has_many :languages, through: :translations
  scope :language, -> (id) {joins(:translations).where('translations.language_id = 1')}

  def translation_from_language(language)
    self.translations.where(language: language).take
  end
end

class Translation < ActiveRecord::Base
  belongs_to :input
  belongs_to :language
  before_save :default_values

  #Apenas para testar o scope de search
  scope :search, -> (part) { where("LOWER(value) LIKE ?", "%#{part.downcase}%") }

  # Se nao setar um input manualmente, irá criar um novo
  def default_values
    self.input ||= Input.create
  end
end

class Language < ActiveRecord::Base
  has_many :translations
  has_many :inputs, through: :translations
end

Answer 1

所以我的解决方案就是创建一个类似的查询

Input.where("id IN ( SELECT input_id
                     FROM translations
                     WHERE language_id = 1
                   )
             AND id NOT IN (
                     SELECT input_id
                     FROM translations
                     WHERE language_id = 2
                   )")