Question

使用Rails 4.2.2我创建了以下迁移以向模型Users添加counter_cache，每当我运行rake db：migrate时，计数器会正确显示当前：book_shelf_count，但是当它更改时它不会更新< / p>

add_shelf_book_count.rb

class AddShelfBookCount < ActiveRecord::Migration
  def self.up
    add_column :users, :book_shelf_count, :integer, default: 0

    User.reset_column_information

    User.find_each { |user| User.reset_counters user.id, :shelf_books }

  end

  def self.down
    remove_column :users, :book_shelf_count
  end

end

user.rb

class User < ActiveRecord::Base
  has_many :shelf_books, through: :shelves, dependent: :destroy
end

shelf.rb

class Shelf < ActiveRecord::Base
  has_many :shelf_books, dependent: :destroy
  belongs_to :user, counter_cache: :book_shelf_count
end

shelf_book.rb

class ShelfBook < ActiveRecord::Base
  belongs_to :shelf
end

Answer 1

问题是ShelfBook是独立于Shelf创建或销毁的，因此无法从Shelf更新counter_cache。为了解决这个问题，我需要在 shelf_book.rb

中实施递增计数器和递减计数器方法

class ShelfBook < ActiveRecord::Base
  belongs_to :shelf
  after_create :increment_counter_cache
  after_destroy :decrease_counter_cache

  def increment_counter_cache
    User.increment_counter(:book_shelf_count, find_user)
  end

  def decrease_counter_cache
    User.decrement_counter(:book_shelf_count, find_user)
  end

  def find_user
    Shelf.find(self.shelf_id).user
  end

Rails 4.2.2 counter_cache没有更新

1 个答案: