如何在 habtm 关联的 Rails 中进行批量更新

Question

I have two models:

#user.rb

has_and_belongs_to_many :groups

#group.rb

has_and_belongs_to_many :users

I want to associate groups to users such that many users can be associated to many groups .

Front end side of the application is sending the user_ids and group_ids to the update method.

So in the UsersController , i've found out each user and associated that user with the groups.

def update
  users = User.where(id: [325, 326])
  users.each { |user| user.update(group_ids: [1, 2])}
end

I need to know the standard way of updating the associated records and what is the most efficient way of updating associated records?

Answer 1

There is a method update_all

def update
  users = User.where(id: [325, 326])
  users.update_all group_ids: [1, 2]
end

Answer 2

The simplest ActiveRecord-native approach is to create a model class for your join table and use that, eg:

class GroupsUser < ActiveRecord::Base; end

(Note that the model class is GroupsUser so that by convention ActiveRecord will know it's for the groups_users table. It's a little goofy but it works.)

Then you can use insert_all on the join table:

user_ids = [325, 326]
group_ids = [1, 2]

values = user_ids.map do |uid| 
           group_ids.map do |gid|
             { user_id: uid, group_id: gid }
           end
         end.flatten
# => [{user_id: 325, group_id: 1}, {user_id: 325, group_id: 2}, {user_id=>326, group_id: 1}, {user_id: 326, group_id: 2}]

GroupsUser.insert_all(values)

Note though that this is is insert_all , not update_all -- update_all doesn't really make sense for a join table. We're adding values, not replacing them. (At least on PostgreSQL and SQLite, if there's a unique index on the join table, duplicates will be ignored -- on MySQL you might need to jump through some more hoops to exclude existing relationships, unless you're deleting those anyway as below.)

If you want to replace any existing associations, you'll need to delete those explicitly:

ActiveRecord::Base.transaction do
  GroupsUser.delete_all(user_id: user_ids)
  # and/or GroupsUser.delete_all(group_id: group_ids), depending
  GroupsUser.insert_all(values)
end

Also worth noting: there's no need to put GroupsUser in app/models/groups_user.rb ; if this is the only code that uses it, you can put it right in the file where it's used. This is especially useful in migrations.