Can't return array elements from array of string using instance variables

Question

I have this model with an array of strings as one of the columns

  create_table "shows", force: :cascade do |t|
    t.time "st"
    t.time "ed"
    t.integer "money"
    t.string "av_seats", default: "--- []\n"
    t.string "oc_seats", default: "--- []\n"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.integer "theatre_id"
    t.integer "screen_id"
    t.integer "movie_id"
    t.index ["movie_id"], name: "index_shows_on_movie_id"
    t.index ["screen_id"], name: "index_shows_on_screen_id"
    t.index ["theatre_id"], name: "index_shows_on_theatre_id"
  end

I'm trying to reference av_seats and oc_seats in another model's controller via this logic

def create
    @booking = Booking.new(booking_params)
    @av_seats = Show.find(params[:show_id]).pluck(:av_seats)
    @oc_seats = Show.find(params[:show_id]).pluck(:oc_seats)

    if @booking.save
      if @av_seats.include? @booking.seat
        @oc_seats << @booking.seat
        @av_seats.delete @booking.seat
      end
      render json: @booking, status: :created, location: @booking

Essentially, it's supposed to move an element from one array to another and delete the same element from the previous array all based on input.

"status": 404,
    "error": "Not Found",
    "exception": "#<ActiveRecord::RecordNotFound: Couldn't find Show without an ID>",

I've tried using the pluck method beforehand and then attempt to use find for the element but I may not be doing it right either.

    @av = Show.pluck(:show_id, :av_seats)
    @oc = Show.pluck(:show_id, :oc_seats)

    @av_seats = Show.find(@av)
    @oc_seats = Show.find(@oc)

# routes.rb

Rails.application.routes.draw do
  resources :movies
  resources :bookings
  resources :shows
  resources :screens
  resources :theatres
  resources :users
end

This is what the form typically looks like. It's an API so no views, just pure JSON.

{
    "booking": {
        "user_id": 1,
        "show_id": 2,
        "screen_id": 2,
        "seat": "A5"
    }
}

If you're getting Couldn't find Show without an ID is because nothing comes in params[:show_id]. — Alter Lagos
– Alter Lagos, Commented Mar 22, 2022 at 21:11
can you show the contents of params, contents of routes.rb and the form that leads to the create action please. — Pascal
– Pascal, Commented Mar 22, 2022 at 22:31

Pascal · Accepted Answer · 2022-03-23 13:52:58Z

1

You create a Booking resource. The information (:show_id) is nested under the :bookings key in your params

I assume you got the following method on the BookingsController

def booking_params
  params.require(:booking).permit(:show_id, :user_id, :seat, :screen_id)
end

?

If your Booking has the association setup properly

class Booking < ApplicationRecord
  belongs_to :show
end

Then you can access the show like this:

booking = Booking.new(booking_params)
show = booking.show

If no association is setup, then you can use

show = Show.find(params[:booking][:show_id])
# or
show = Show.find(booking_params[:show_id]) # not _params_

Since the show object is loaded anyhow, you can just access av_seats and oc_seats directly

show.av_seats
show.oc_seats

pluck is an optimization where only the columns you pluck are fetched from the DB.

You probably want to change the xx_seats columns to be of type string[] (with array: true in your migration).

Once you change the contents of the seats array(s) you need to save the show record.

answered Mar 23, 2022 at 13:52

Pascal

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3 Comments

Lazlo Over a year ago

Oh nice, yeah, I see what you mean. I managed to get it to finally resolve the error and it copies the characters just fine. But it doesn't delete it from oc_seats for some reason. Also, they already are strings, sqlite3 is just weird with how it does array of strings and it took some finnicking around.

Pascal Over a year ago

Ah, sqlite does not support array types. So You might need to serialize and deserialize your array on your own. I don't use sqlite so not sure what the common way is though.

Lazlo Over a year ago

I wouldn't worry about that, I figured that out before having this issue haha. In any case, I appreciate the help. I've managed to solve the error. It wasn't saving show afterwards so the effects wouldn't take place so I added a show.save to the logic.

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