Array results using Active Record Query Model 'select' and 'where'

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?

santuxus · Accepted Answer · 2011-10-27 09:04:31Z

4

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)

answered Oct 27, 2011 at 9:04

santuxus

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Comments

tbuehlmann · Accepted Answer · 2011-10-27 09:02:58Z

2

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

answered Oct 27, 2011 at 9:02

tbuehlmann

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Comments

Jaycreation · Accepted Answer · 2017-05-09 14:18:47Z

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(", ")})")

answered May 9, 2017 at 14:18

Jaycreation

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Comments

Salil · Accepted Answer · 2011-10-27 08:59:45Z

1

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])

answered Oct 27, 2011 at 8:59

Salil

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Comments

iblue · Accepted Answer · 2012-07-30 22:07:04Z

1

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

edited Jul 30, 2012 at 22:07

iblue

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answered Oct 27, 2011 at 9:04

nkm

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