使用Rails从具有多个组的组中检索具有所有组的用户

Question

I have an app in which users have many groups and groups have many users, through a GroupUsers join table.

I'd like to get all the Users in exactly all of the groups of a given array of groups.

It sounds quite simple, yet I've not managed to find a way to do it.

This is what I tried ( all_groups is the array of groups) :

users = User
all_groups.each do |group| 
  users = users.joins(:group_users).where("group_users.group_id = ?", group.id)
end   

I always get no result, so I tried this to understand what's going on :

users = User

group1 = all_groups.first 
group2 = all_groups.last 

users1 = users.joins(:group_users).where("group_users.group_id = ?", group1.id)
users2 = users1.joins(:group_users).where("group_users.group_id = ?", group2.id)  

users1 is an array with all the users in group1 as expected, but users2 is always empty.

Does someone have a clue about how to solve this ?

EDIT : Answer :

users = User
all_groups.each do |group| 
  users = User.including_ids(users.map(&:id)).joins(:group_users).where("group_users.group_id = ?", group.id)
end  

With in models/user.rb :

scope :including_ids, ->(*ids) {
  where(arel_table[:id].in(ids))
}

That's not really beautiful but it's working.

Answer 1

based on the explanation you gave, I assume you have something like:

class User
  has_many :group_users
  has_many :groups, through: :group_users
end

class GroupUser
  belongs_to :user
  belongs_to :group
end

class Group
  has_many :group_users
  has_many :users, through: :group_users
end

If yes, you can probably do the following:

# get groups
groups = Group.where( ......some condition here ) 

# as long as groups is an ActiveRecord::Relation type you can use 'pluck'
User.joins( :group_users ).where( 'group_users.group_id IN (?)', groups.pluck(:id) ).uniq

Hope that helps. :)

Cheers!