Ruby on rails 基于嵌套模型计数排序的Rails查询?
我有两个模型:组和组成员Ruby on rails 基于嵌套模型计数排序的Rails查询?,ruby-on-rails,ruby-on-rails-3,activerecord,Ruby On Rails,Ruby On Rails 3,Activerecord,我有两个模型:组和组成员 我想返回按最高GroupMember计数排序的组?如何在Rails中设置这种类型的连接/查询计数?使用计数器缓存,生活会轻松得多: $ rails g migration add_group_member_counts_to_groups # migration def change add_column :groups, :group_members_count, :integer, default: 0 end class GroupMember <
我想返回按最高GroupMember计数排序的组?如何在Rails中设置这种类型的连接/查询计数?使用计数器缓存,生活会轻松得多:
$ 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
因为reset_计数器不接受ID数组
将来,您将写:
ids = Group.pluck(:id)
我等不及了-
class Group < ActiveRecord::Base
has_many :group_members
default_scope order('(select count(1) from group_members where group_members.group_id = groups.id) desc')
end
请注意,这将在order子句中创建一个子查询,这可能会对许多组记录产生显著的SQL减速。如果经常使用此信息,最好按照Delba的建议使用计数器缓存。谢谢,但出于各种原因,我现在不想使用计数器缓存。如何使用Rails实现这一点?感谢+1提供了有用的重置计数器代码-也不知道如何拔出-很好。
class Group < ActiveRecord::Base
has_many :group_members
default_scope order('(select count(1) from group_members where group_members.group_id = groups.id) desc')
end