Overriding displayed attributes without an id always returns zero results

[bendangelo]

Description

I had AI write some code for me and it wrote out a displayed_attributes line but didn't include the id, this caused no results to always be returned. I used AI to expand on what is going on, please forgive me. Basically, an error should be shown or it should always include the primary id.

Since internally the search results to fetch records from the database via .where(id: hit_ids), the absence of the ID in the Meilisearch response prevents the gem from mapping hits back to ActiveRecord/Sequel models. The library should either automatically include the primary key in displayed_attributes or raise a configuration error when it is missing.

Expected behavior

The gem should successfully return model instances even if :id is not explicitly listed in displayed_attributes, OR it should warn the developer that the primary key is required for the "Search -> DB Lookup" flow to function.

Current behavior

The search returns a Meilisearch::Rails::Pagination object where the results are empty (or contain nil values) because hit_ids evaluates to [nil].

Environment

Operating System: Ubuntu / Linux Mint
Meilisearch version: v1.32.2
meilisearch-rails version: v0.16.0
rails version: v8.0.2

Reproduction script:

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"
  ruby '3.3.0' # Adjust to your local version

  gem 'minitest'
  gem 'rails', '~> 8.0'
  gem 'sqlite3'
  gem 'meilisearch-rails'
end

require 'minitest/autorun'
require 'active_record'

# Setup Meilisearch
Meilisearch::Rails.configuration = {
  meilisearch_host: ENV.fetch('MEILISEARCH_HOST', 'http://127.0.0.1:7700'),
  meilisearch_api_key: ENV.fetch('MEILISEARCH_API_KEY', 'masterKey'),
}

# ActiveRecord Setup
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Schema.define do
  create_table :books do |t|
    t.string :title
    t.string :author
  end
end

class Book < ActiveRecord::Base
  include Meilisearch::Rails

  meilisearch do
    attribute :title, :author
    searchable_attributes [:title]
    # BUG: Omitting :id here causes ms_search to fail
    displayed_attributes [:title, :author] 
  end
end

class BugTest < Minitest::Test
  def setup
    Book.destroy_all
    Book.create!(title: "The Great Gatsby", author: "F. Scott Fitzgerald")
    Book.reindex!
    
    # Wait for Meilisearch to process the index
    task = Meilisearch::Rails.client.tasks['results'].first
    Meilisearch::Rails.client.wait_for_task(task['uid'])
  end

  def test_search_fails_when_id_is_not_displayed
    results = Book.search("Gatsby")
    
    # This will fail. results.count will be 0 or results will contain [nil]
    # because the gem couldn't find the 'id' in the hits JSON to perform the DB lookup.
    assert_equal 1, results.count, "Search should return 1 book even if id is not in displayed_attributes"
    assert_instance_of Book, results.first
  end
end