Rails的查询排序基于嵌套模型的数量？ [英] Rails query that sorts based on the count of a nested model?

问题描述

我有两个型号：组放大器; GroupMember

I have two models: Group & GroupMember

我想回组，排序最高的GroupMember算？您如何设置这种类型的连接/查询计数的Rails？

I would like to return Groups, sorted by the highest GroupMember Count? How do you setup this type of join/query count in Rails?

推荐答案

生命是如此容易得多与counter_cache：

Life is so much easier with counter_cache:

$ rails g migration add_group_member_counts_to_groups

# migration
def change
  add_column :groups, :group_members_count, :integer, default: 0
end

class GroupMember < ActiveRecord::Base
  belongs_to :group, counter_cache: true
end

class Group < ActiveRecord::Base
  has_many :group_members
  scope :order_by_group_members_count, order('group_members_count DESC')
end

Group.order_by_group_members_count # => What you're looking for

只有一个查询，只对团体表。

Only one query, only on the groups table.

修改

如果您需要重置group_members_count：

If you need to reset the group_members_count:

ids = Group.select(:id).map &:id
ids.each do |id|
  Group.reset_counters(id, :group_members)
end

（因为reset_counters并不需要一组ID）

(because reset_counters doesn't take an array of ids)

在今后的Rails 3.2.0 ，你会写：

ids = Group.pluck(:id)

我不能等待; - ）

I can't wait ;-)

这篇关于Rails的查询排序基于嵌套模型的数量？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！