ruby-on-rails - Rails 3 等同于复杂的 SQL 查询

Question

给定以下模型:

class Recipe < ActiveRecord::Base
  has_many :recipe_ingredients
  has_many :ingredients, :through => :recipe_ingredients
end

class RecipeIngredient < ActiveRecord::Base
  belongs_to :recipe
  belongs_to :ingredient
end

class Ingredient < ActiveRecord::Base
end

如何在 Rails 3 中使用 Arel 执行以下 SQL 查询？

SELECT * FROM recipes WHERE NOT EXISTS (
  SELECT * FROM ingredients WHERE 
    name IN ('chocolate', 'cream') AND 
    NOT EXISTS (
      SELECT * FROM recipe_ingredients WHERE 
        recipe_ingredients.recipe_id = recipes.id AND 
        recipe_ingredients.ingredient_id = ingredients.id))

Answer 1

我不确定如何使用 Arel 或 ActiveRecord 进行关系除法。如果可以接受执行两个查询，则这将是等效的:

with_scope(includes(:recipes)) do
  cream_recipes = Ingredient.where(:name => "cream").first.recipes
  chocolate_recipes = Ingredient.where(:name => "chocolate").first.recipes
end
@recipes_with_chocolate_and_cream = cream_recipes & chocolate_recipes

或者您可以直接使用 find_by_sql 传递 SQL .