具有多态关联的范围和查询

Question

我发现很少有关于如何在rails中编写多态关联的范围,更不用说如何在多态关联上编写查询.

在Rails文档中,我查看了" 多态关联"部分," 连接表"部分和" 范围"部分.我也做了相当广泛的谷歌搜索.

以此设置为例:

class Pet < ActiveRecord::Base
  belongs_to :animal, polymorphic: true
end

class Dog < ActiveRecord::Base
  has_many :pets, as: :animal
end

class Cat < ActiveRecord::Base
  has_many :pets, as: :animal
end

class Bird < ActiveRecord::Base
  has_many :pets, as: :animal
end

所以Pet可以是animal_type"狗","猫"或"鸟".

要显示所有表结构:这是我的schema.rb:

create_table "birds", force: :cascade do |t|
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end

create_table "cats", force: :cascade do |t|
  t.integer  "killed_mice"
  t.datetime "created_at",  null: false
  t.datetime "updated_at",  null: false
end

create_table "dogs", force: :cascade do |t|
  t.boolean  "sits"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end

create_table "pets", force: :cascade do |t|
  t.string   "name"
  t.integer  "animal_id"
  t.string   "animal_type"
  t.datetime "created_at",  null: false
  t.datetime "updated_at",  null: false
end

然后我继续做了一些记录:

Dog.create(sits: false)
Dog.create(sits: true)
Dog.create(sits: true) #Dog record that will not be tied to a pet
Cat.create(killed_mice: 2)
Cat.create(killed_mice: 15)
Cat.create(killed_mice: 15) #Cat record that will not be tied to a pet
Bird.create

然后我去做了一些pet记录:

Pet.create(name: 'dog1', animal_id: 1, animal_type: "Dog")
Pet.create(name: 'dog2', animal_id: 2, animal_type: "Dog")
Pet.create(name: 'cat1', animal_id: 1, animal_type: "Cat")
Pet.create(name: 'cat2', animal_id: 2, animal_type: "Cat")
Pet.create(name: 'bird1', animal_id: 1, animal_type: "Bird")

这就是设置!现在困难的部分:我想在Pet模型上创建一些范围,挖掘多态关联.

以下是我想写的一些范围:

• 给我所有Pets可以坐的动物类型=="狗"
• 给我所有Pets杀死至少10只老鼠的animal_type =="Cat"
• 给我所有Pets不是animal_type"狗"的东西,不能坐.(换句话说:给我所有的宠物:所有的宠物:除了不能坐的狗)

所以在我的Pet模型中,我想把我的范围放在那里:

class Pet < ActiveRecord::Base
  belongs_to :animal, polymorphic: true

  scope :sitting_dogs, -> {#query goes here}
  scope :killer_cats, -> {#query goes here}
  scope :remove_dogs_that_cannot_sit, -> {#query goes here} #only removes pet records of dogs that cannot sit. All other pet records are returned
end

我发现编写这些范围非常困难.

我在网上找到的一些东西看起来你只能用原始SQL编写这些范围.我想知道是否可以使用Hash语法来代替这些范围.

任何提示/帮助将不胜感激!

Answer 1

在回顾了之前的答案并尝试过之后：这就是我要做的工作。

（请注意，Pet.remove_dogs_that_cannot_sit返回一个数组。此类方法是可读的，但具有速度慢的缺点N + 1。任何修复此问题的建议将不胜感激。）

class Dog < ActiveRecord::Base
  has_many :pets, as: :animal
  scope :sits, -> {where(sits: true)}
end

class Cat < ActiveRecord::Base
  has_many :pets, as: :animal
  scope :killer, ->{ where("killed_mice >= ?", 10) }
end

class Pet < ActiveRecord::Base
  belongs_to :animal, polymorphic: true

  scope :by_type, ->(type) {where(animal_type: type)}
  scope :by_dogs, -> {by_type("Dog") }
  scope :by_cats, -> {by_type("Cat") }

  def self.sitting_dogs
    all.by_dogs
       .joins("INNER JOIN dogs on animal_type = 'Dog' and animal_id = dogs.id")
       .merge(Dog.sits)
  end

  def self.killer_cats
    all.by_cats
       .joins("INNER JOIN cats on animal_type = 'Cat' and animal_id = cats.id")
       .merge(Cat.killer)
  end

  # returns an Array not Pet::ActiveRecord_Relation
  # slow due to N + 1
  def self.remove_dogs_that_cannot_sit
    all.reject{|pet| pet.animal_type == "Dog"  && !pet.animal.sits}
  end
end