如何在没有有效关联 ID 的情况下执行自动清除关联表行

Question

我正在尝试找到一种方法来清除与另一个表关联的表中的行。

关键是我正在尝试为食谱创建应用程序。 例如，我不想遇到两个或更多食谱具有相同成分（比如说鸡蛋）的情况。如果我删除一个配方，它将自动删除关联的 Active Record，但我想在例如鸡蛋不会在另一个食谱中使用。

成分模型：

class Ingredient < ApplicationRecord
  belongs_to :recipe, inverse_of: :ingredients

end

配方模型：

class Recipe < ApplicationRecord
    has_many :ingredients, inverse_of: :recipe
    has_many :directions, inverse_of: :recipe

    accepts_nested_attributes_for :ingredients,
                                    reject_if: proc { |attributes| attributes['name'].blank? },
                                    allow_destroy: true
    accepts_nested_attributes_for :directions,
                                    reject_if: proc { |attributes| attributes['step'].blank? },
                                    allow_destroy: true

    validates :tittle, :description, :image, presence: true
    has_attached_file :image, styles: { :medium => "400x400#" }
    validates_attachment_content_type :image, content_type: /\Aimage\/.*\Z/
end

那么有没有办法（不包括sql查询）来执行这样的操作？

Answer 1

首先创建一个连接配方和成分的连接表。这是设置多对多关联所必需的。

class Recipe < ApplicationRecord
  has_many :recipe_ingredients
  has_many :ingredients, through: :recipe_ingredients

  accepts_nested_attributes_for :ingredients,
     reject_if: proc { |attributes| attributes['name'].blank? },
     allow_destroy: true

  # ...
end

# This model is the master table for ingredients 
# using a normalized table avoids duplication
class Ingredient < ApplicationRecord
  has_many :recipe_ingredients
  has_many :ingredients, through: :recipe_ingredients
end

# This contains the quantity of an ingredient used in a recipe
class RecipeIngredient < ApplicationRecord
  belongs_to :recipe
  belongs_to :ingredients
end

然后您可以通过创建回调来删除孤立的行：

class RecipeIngredient < ApplicationRecord
  belongs_to :recipe
  belongs_to :ingredients

  after_destroy do |record|
    ingredient = record.ingredient
    unless ingredient.recipe_ingredients.any?
      ingredient.destroy
    end
  end
end