[RUBY] [Rails] Talk about paying attention to the return value of where

Introduction

Why i wrote

--Do not understand where or pluck return values and share your jammed experience ――With the meaning of remorse for abusing ActiveRecord, saying "You can go with .id "

Conclusion

-~~ where and pluck return values are arrays ~~ → pluck is returned as an array --where returns ActiveRecord :: Relation * Addition 20/11/10 --Understand how to use ActiveRecord method chains

Premise

environment

・ Ruby 2.6.5 ・ Rails 6.0.3 -Use devise (user model)

ER diagram

rooms table: manage rooms to DM user_rooms table: Manage user and room combinations

Thing you want to do

The image is the user_rooms table.

What you want to do
I want to get the user information of the DM partner (id = 10)
Conditions
The room to DM is room_id: 2 I (current_user) is user_id: 15

Event

I tried to realize it with the code below

rooms_controller.rb

class RoomsController < ApplicationController
  def show
      @room = Room.find(params[:id])
      current_user_room = @room.user_rooms.where.not(user_id: current_user.id)
      user_id = current_user_room.user_id
      @user = User.find(user_id)
  end
end

Line 3: Define @room (id: 2) with two users participating. Line 4: Get the @room and user combination with @ room.user_rooms. (At this point, the records are narrowed down to two.) In addition, where.not (user_id: current_user.id) narrows down to the record that does not include you. 5th line: Of the records obtained in the 4th line, we are trying to get the user_id.

However, on the 4th line, the following error occurs.

[*] pry(main)> current_user_room.user_id

#result
NoMethodError: undefined method `user_id' for #<UserRoom::ActiveRecord_AssociationRelation:0x00007fbef39437e8>

？？？ For the time being, I will output current_user_room

[**] pry(main)> current_user_room

#result
=> [#<UserRoom:0x00007fbeefb36518
  id: 2,
  user_id: 10,
  room_id: 2,
  created_at: Sat, 07 Nov 2020 04:00:28 UTC +00:00,
  updated_at: Sat, 07 Nov 2020 04:00:28 UTC +00:00>]

Why can't I? Try to get it with find using id = 2

[**] pry(main)> user_room1 = UserRoom.find(2)

#result
=> #<UserRoom:0x00007fbeec46c960
 id: 2,
 user_id: 10,
 room_id: 2,
 created_at: Sat, 07 Nov 2020 04:00:28 UTC +00:00,
 updated_at: Sat, 07 Nov 2020 04:00:28 UTC +00:00>

At first, the result looked the same, but if you look closely, the current_user_room has[]and is in an array ~~. ~~ → Addition The current_user_room was fetched by the ** where method **. ~~ You can't get it by applying a method chain to an array. Of course, the where method takes a set of data. ~~ By the way, I tried to get the user_id with the pluck method, but the result was the same.

solution

~~ It seems to be solved if you pick it up from the array. ~~ So [Rails Guide](https://railsguides.jp/active_record_querying.html#%E3%83%A1%E3%82%BD%E3%83%83%E3%83%89%E3%83%81 % E3% 82% A7% E3% 82% A4% E3% 83% B3% E3% 82% 92% E7% 90% 86% E8% A7% A3% E3% 81% 99% E3% 82% 8B) Looking at it, it seems that the take method can be used. I know I want to get one.

The take method takes one record. It does not specify which records are retrieved.

rooms_controller.rb

#Original code
current_user_room = @room.user_rooms.where.not(user_id: current_user.id)

#Corresponding code(At the end.Add take)
current_user_room = @room.user_rooms.where.not(user_id: current_user.id).take

• Alternatively, you can also add [0] to get the first array in the end.

Modified code

rooms_controller.rb

class RoomsController < ApplicationController
  def show
    @room = Room.find(params[:id])
    current_user_room = @room.user_rooms.where.not(user_id: current_user.id).take #.Add take
    user_id = current_user_room.user_id
    @user = User.find(user_id)

    @messages = @room.messages.includes(:user)
    @message = Message.new
  end
end

Postscript

It turns out that where returns an instance of ActiveRecord :: Relation, not an array.

# (where) current_user_Check room class
pry(main)> current_user_room.class
=> UserRoom::ActiveRecord_AssociationRelation

# (find) user_Also check room1
pry(main)> user_room.class
=> UserRoom(id: integer, user_id: integer, room_id: integer, created_at: datetime, updated_at: datetime)

I'm still not familiar with it, so I'll take a closer look at ActiveRecord and ActiveRecord :: Relation.

in conclusion

For the time being, we have taken measures that can be taken in the current situation, but if we review it from the ground up, it may not even be necessary to describe this in the first place. I want to fix it as soon as I notice it. However, this time, it was a good study to be able to touch the behavior of where. I would like to improve it further, so I would appreciate it if you could point out any deficiencies or other methods.

Reference material

Rails Guide The difference between find and where in ActiveRecord. → I was very helpful in the postscript.