How to avoid undefined method `id' for ActiveRecord_Relation?

Question

Hopefully this is not a duplicate question, as I have spent weeks scouring StackOverflow for answers and have not found a solution to my problem.

I have a Ruby on Rails API (Ruby 1.9.3, Rails 4.0.0) and am using ActiveRecord to interact with our database. When a request is made to retrieve the currently scheduled banner, it works perfectly. When no banner is scheduled, however, a 500 response is experienced:

undefined method `id' for #\u003cBanner::ActiveRecord_Relation:0x0000000628fba8\u003

My understanding is that this is because an inherent "id" method is being attempted upon a "nil" which is the result from the database lookup when no qualifying record is found. How do I gracefully handle this scenario so that a 500 error is not encountered and so that I may return a more polite response to the requester?

Here is my controller:

class BannersController < ApplicationController
  load_and_authorize_resource

  respond_to :json

  # Look to see if any banners should be showing right now
  def current
    @banner = Banner.current
  end
end

Here is my model:

class Banner < ActiveRecord::Base
  self.table_name   = 'Banner'
  self.primary_key  = :BannerID

  alias_attribute :name,              :FriendlyName
  alias_attribute :banner_html,       :BannerHtml
  alias_attribute :banner_image,      :BannerImage
  alias_attribute :start_date,        :StartDate
  alias_attribute :end_date,          :EndDate
  alias_attribute :is_active,         :IsActive
  alias_attribute :is_removed,        :IsRemoved
  alias_attribute :start_date_time,   :StartDateTime
  alias_attribute :end_date_time,     :EndDateTime
  alias_attribute :hidden_text,       :HiddenText
  alias_attribute :hidden_background_color,       :HiddenBackgroundColor

  # This returns nil if no banner is scheduled, which then causes the view to return a 500 response because it tries to invoke an "id" method
  scope :current, -> { Banner.where("StartDateTime <= ? AND EndDateTime >= ? AND IsActive=1 AND IsRemoved=0 AND BannerType=1", Time.now.to_s(:db), Time.now.to_s(:db)).first }  
end

Note: I have tried using .find_by and also tried not using .first, but still cannot seem to find a resolution to this.

Here is my view:

json.extract! @banner, :id, :banner_html, :banner_image, :hidden_text, :hidden_background_color

json.request_id request.uuid

The database table "Banner" has a primary key of "BannerID".

Thanks to all who would take the time to look into this. I have spent untold hours reading and trying everything in order to remedy the situation, to no avail.

Try changing :id to :banner_id in json.extract! line

Pavan
– Pavan

2017-06-25 11:21:01 +00:00
Commented Jun 25, 2017 at 11:21 — Pavan
– Pavan, Commented Jun 25, 2017 at 11:21
What is an ActiveRecord_Relation?

engineersmnky
– engineersmnky

2017-06-26 15:00:28 +00:00
Commented Jun 26, 2017 at 15:00 — engineersmnky
– engineersmnky, Commented Jun 26, 2017 at 15:00

Pavan · Accepted Answer · 2017-06-25 11:27:15Z

1

undefined method `id' for \u003cBanner::ActiveRecord_Relation:0x0000000628fba8\u003

The database table "Banner" has a primary key of "BannerID"

Then whey are using :id still!. Change

json.extract! @banner, :id, :banner_html, :banner_image, :hidden_text, :hidden_background_color

to

json.extract! @banner, :BannerID, :banner_html, :banner_image, :hidden_text, :hidden_background_color

Small Note:

By convention, the attributes should be in snake_case.

answered Jun 25, 2017 at 11:27

Pavan

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3 Comments

RavingHermit Over a year ago

Thank you so much for your help! I'm new to Ruby and your help is a lifesaver. When I made the change you suggested, I now get this response: undefined method 'BannerID' for #\u003cBanner::ActiveRecord_Relation

Pavan Over a year ago

@RavingHermit What is the field name in the table? is it BannerID or banner_id?

RavingHermit Over a year ago

The table field is BannerID in the database.

m3characters · Accepted Answer · 2017-06-25 12:53:01Z

0

Why don't you just

if [email protected]?
  json.extract...
  ...
else
  json.null!
  (or whatever you want?)
end

answered Jun 25, 2017 at 12:53

m3characters

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3 Comments

RavingHermit Over a year ago

I smell what you are cooking and I like it. Unfortunately, I still get the same error: undefined method 'id' for #\u003cBanner::ActiveRecord_Relation:0x00000007134640\u003e

RavingHermit Over a year ago

This is my updated view:

if [email protected]?     json.extract! @banner, :id, :banner_html, :banner_image, :hidden_text, :hidden_background_color     json.request_id request.uuid else     json.null! end

m3characters Over a year ago

Another way to handle it, that would actually be better maybe, would be to have a model.method that returns a "default" non available banner, and in the controller check: @banner = Banner.current like you have but followed by @banner = Banner.default unless @banner

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