Is there a way to create a Ruby model scope for ordering books? (none numeric, none alphabetic)

Assuming you may have multiple quotes per book (and will be adding more books over time - without wanting to add new lines to your code), you might want to normalise your data a little better by having a books table, storing the book sort field to capture the preferred sort order for the books (instead of that living in code directly);

# models/book.rb
class Book < ApplicationRecord
  validates :sort, presence: true
end

# models/quote.rb
class Quote < ApplicationRecord
  belongs_to :book
end

# db/schema.rb
create_table "books", force: :cascade do |t|
    t.string "title", null: false
    t.string "author"
    t.integer "sort", null: false
end
create_table "quotes", force: :cascade do |t|
    t.string "text", null: false
    t.bigint "book_id", null: false # < new column
    t.integer "reference_chapter", null: false
    t.integer "reference_paragraph", null: false
    t.integer "reference_sentence", null: false
    t.string "image"
    t.text "notes"
    # TODO: you will also want a foreign key constraint here for quote.book_id
end

Then you could use this relationship to sort quotes, passing multiple columns to the order method - i.e. sort by book.sort first, then by reference_chapter (for any quotes in the same book), then by reference_paragraph (for any quotes in the same chapter) etc. As a best practice, I would suggest using quotes.id as a final disambiguator in case there were multiple quotes from the same book+chapter+paragraph+sentence.

# models/quote.rb
class Quote < ApplicationRecord
  scope :sorted, -> { joins(:book).order('books.sort ASC, reference_chapter ASC, reference_paragraph ASC, reference_sentence ASC, id ASC') }
end

I found a workaround. It does not answer my initial question of creating a scope, but it does solve the issue of my code not working for instances like quote.image

Solution

In my controller when I coded this:

@temp_array << @quotes.select { |quote| quote[:reference_book] == book}
@sorted_quotes << @temp_array

it would put the ActiveRelation inside an array element and then save it to the @temp_array; this is because select pulls all of the instances out of one array that matches the search terms. So, I just needed to undo this by iterating through the @temp_array and adding each element to the @sorted_quotes instead of adding the entire thing.

Here are my changes (also changing some variables to not be 'global' as that's just not needed in this situation.

def quotes
    quotes = Quote.all
    @sorted_quotes = []
    
    order_of_books.each do |book|
        temp_array = []
        if quotes.any? { |quote| quote[:reference_book] == book}
            temp_array << quotes.select { |quote| quote[:reference_book] == book}
            temp_array[0].each do |v|
                @sorted_quotes << v
            end
        end
    end
end

This fixed the issue. I can leave the question open as this solution does not technically answer the initial question about making a scope to do this same thing.