具有条件的列的计数器缓存? [英] Counter Cache for a column with conditions?

问题描述

我不熟悉计数器缓存的概念，而且我的应用主页之一的加载时间过长，我相信我需要继续下去.

I am new to the concept of counter caching and with some astronomical load times on one of my app's main pages, I believe I need to get going on it.

我需要实现的大多数计数器缓存都附加了某些(简单的)条件.例如，这是一个常见的查询:

Most of the counter caches I need to implement have certain (simple) conditions attached. For example, here is a common query:

@projects = employee.projects.where("complete = ?", true).count

当我显示一个列出公司所有员工的项目计数的表单时，我遇到了上述 N+1 查询问题.

I am stumbling into the N+1 query problem with the above when I display a form that lists the project counts for every employee the company has.

我真的不知道我在做什么所以请纠正我！

I don't really know what I'm doing so please correct me!

# new migration
add_column :employees, :projects_count, :integer, :default => 0, :null => false

# employee.rb
has_many :projects

# project.rb
belongs_to :employee, :counter_cache => true

迁移之后……这就是我需要做的全部吗?

After migrating... is that all I need to do?

我如何才能在我提到的条件下工作以最大限度地减少加载时间?

How can I work in the conditions I mentioned so as to minimize load times?

推荐答案

关于 counter_cache 的条件，我会读这个 博文.

With regards to the conditions with counter_cache, I would read this blog post.

您应该做的一件事是将以下内容添加到迁移文件中:

The one thing you should do is add the following to the migration file:

 add_column :employees, :projects_count, :integer, :default => 0, :null => false

 Employee.reset_column_information

 Employee.all.each do |e|
   Employee.update_counters e.id, :projects_count => e.projects.length
 end

因此，您当前的项目计数可以迁移到与每个 Employee 对象关联的新 projects_count.在那之后，你应该很高兴.

So you current projects count can get migrated to the new projects_count that are associated with each Employee object. After that, you should be good to go.

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