使用Active Record查询模型“选择”和“位置”排列结果

Question

I have a user, membership and group model. A user has many memberships, and groups through memberships. A group has many memberships, and users through memberships. Memberships belongs to both.

When a user accesses the users index view I want to show him/her all users that belong to the group he/she belongs to: I created the following code, which does not work. I cannot seem to get the query to work. Pease help!

The code in the Users controller

class UsersController < ApplicationController

  def index
      @users = current_user.relevant_members
  end

end

The code in the User model

def relevant_members
  group_ids = self.group_ids
  user_ids = Membership.select("user_id").where("group_id IN (#{group_ids.join(", ")})")
  User.find(user_ids)
end

I don't understand why, when tested in the console, user_ids is not an array of ids, but the following array:

[#<Membership user_id: 2>, #<Membership user_id: 2>, #<Membership user_id: 3>, #<Membership user_id: 3>, #<Membership user_id: 3>, #<Membership user_id: 2>]

What would be a better way of returning an array of user ids to find all relevant group members?

Answer 1

Membership.select("user_id").where("group_id IN (#{group_ids.join(", ")})")

returns always an array of Membership objects, select("user_id") changes only the fields that are loaded from DB to the object.

It's enough to map it to id

user_ids = Membership.select("user_id").where("group_id IN (#{group_ids.join(", ")})").map(&:user_id)

Answer 2

Did you try the pluck() function ? https://apidock.com/rails/ActiveRecord/Calculations/pluck

user_ids = Membership.pluck("user_id").where("group_id IN (#{group_ids.join(", ")})")

Answer 3

Membership.select('user_id') will return an array of Membership objects with just the user_id attribute, that's correct so far. It will work if you extract the ids from the result:

membershipts = Membership.select("user_id").where("group_id IN (#{group_ids.join(", ")})")
user_ids = memberships.map(&:user_id)

Best regards

Tobias

Answer 4

This is because your user_ids is an object of the class Membership and hence you can't get an array of the 'user_ids' directly

You have to do something like following

  user_ids = Membership.select("user_id").where("group_id IN (#{group_ids.join(", ")})")
  user_ids_array = user_ids.collect{|u| u.user_id}
  User.find(user_ids_array)

Also you can modify your where clause as follow, which is more ruby way.

user_ids = Membership.select("user_id").where(["group_id IN (?)", group_ids])

Answer 5

Membership.where("group_id in (#{groups.collect(&:id).join(',')})")
    .all.collect(&:user_id)