counter_cache 实现的问题 [英] Problem with counter_cache implementation

问题描述

我正在'rake 中止！...posts_count 被标记为只读错误.

I'm getting 'rake aborted! ... posts_count is marked readonly' errors.

我有两个模型:user 和 post.

I have two models: user and post.

users has_many posts.

posts belongs_to :user, :counter_cache => true

我有一个迁移，将 posts_count 列添加到 users 表，然后计算并记录每个用户的当前帖子数.

I have a migration which adds the posts_count column to the users table and then calculates and records the current number of posts per user.

self.up
  add_column :users, :posts_count, :integer, :default => 0

  User.reset_column_information
  User.all.each do |u|
    u.update_attribute( :posts_count, u.posts.count)
  end
end

运行迁移时出现错误.当然，这是非常明确的，如果我从帖子模型中删除 :counter_cache 声明，例如

when I run the migration I get the error. This is pretty clear-cut, of course and if I remove the :counter_cache declaration from the posts model, e.g.

belongs_to :user

迁移运行良好.这显然没有意义，因为您无法以这种方式真正实现它.我错过了什么?

the migration runs fine. This obviously, does not make sense because you couldn't really implement it this way. What am I missing?

推荐答案

您应该使用 User.reset_counters 来执行此操作.此外，我建议使用 find_each 而不是 each 因为它会分批迭代集合，而不是一次迭代所有.

You should be using User.reset_counters to do this. Additionally, I would recommend using find_each instead of each because it will iterate the collection in batches instead of all at once.

self.up
  add_column :users, :posts_count, :integer, :default => 0

  User.reset_column_information
  User.find_each do |u|
    User.reset_counters u.id, :posts
  end
end

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