Many-to-many associations work incorrectly when there is similar foreign key

[hieuk09]

Describe the bug

I have table books with many-to-many relationship with authors via book_authors. However, I also have a column author_id on books to denote the main author.

When querying associations using through:, rom-sql uses the column author_id to combine the associations when query, results in incorrect output.

To Reproduce

Run the below script

require 'rom'

rom = ROM.container(:sql, 'sqlite::memory') do |config|
  config.default.create_table(:books) do
    primary_key :id
    foreign_key :author_id, :authors
  end

  config.default.create_table(:authors) do
    primary_key :id
  end

  config.default.create_table(:book_authors) do
    primary_key :id
    foreign_key :book_id, :books
    foreign_key :author_id, :authors
  end

  config.relation(:books) do
    schema(infer: true) do
      associations do
        has_many :book_authors
      end
    end

    auto_struct true
  end

  config.relation(:authors) do
    schema(infer: true) do
      associations do
        has_many :books, through: :book_authors
      end
    end

    auto_struct true
  end

  config.relation(:book_authors) do
    schema(infer: true) do
      associations do
        belongs_to :book
        belongs_to :author
      end
    end

    auto_struct true
  end
end

class AuthorRepo < ROM::Repository[:authors]
  def all_with_books
    root.combine(books: :book_authors).to_a
  end
end

gateway = rom.gateways[:default]
author_repo = AuthorRepo.new(container: rom)

gateway[:authors].insert(id: 1)
gateway[:authors].insert(id: 2)
gateway[:books].insert(id: 1, author_id: 2)
gateway[:books].insert(id: 2, author_id: 2)
gateway[:book_authors].insert(id: 1, book_id: 1, author_id: 1)
gateway[:book_authors].insert(id: 2, book_id: 2, author_id: 2)
gateway[:book_authors].insert(id: 3, book_id: 1, author_id: 2)

puts author_repo.all_with_books.inspect

# output: 
# [#<ROM::Struct::Author id=1 books=[]>, #<ROM::Struct::Author id=2 books=[#<ROM::Struct::Book id=1 author_id=2 book_authors=[#<ROM::Struct::BookAuthor id=1 book_id=1 author_id=1>, #<ROM::Struct::BookAuthor id=3 book_id=1 author_id=2>]>, #<ROM::Struct::Book id=1 author_id=2 book_authors=[#<ROM::Struct::BookAuthor id=1 book_id=1 author_id=1>, #<ROM::Struct::BookAuthor id=3 book_id=1 author_id=2>]>, #<ROM::Struct::Book id=2 author_id=2 book_authors=[#<ROM::Struct::BookAuthor id=2 book_id=2 author_id=2>]>]>]

Expected behavior

Author 1 should also have one book from the book_authors record 1

My environment

• Affects my production application: YES
• Ruby version: 3.3
• OS: MacOS

[musaffa]

Your book relation has no belongs_to :author.

[musaffa]

config.relation(:books) do
    schema(infer: true) do
      associations do
        belongs_to :author
        has_many :authors, through: :book_authors
      end
    end

    auto_struct true
  end

class AuthorRepo < ROM::Repository[:authors]
  def all_with_books
    root.combine(books: :authors).to_a
  end
end

[hieuk09]

@musaffa thanks for checking, it is intentional that book has no belongs_to :author. In this case, I want to migrate from having author_id column to having the intermediate table book_authors.

On the other hand, even after adding the association, it looks like author 1 record still has no books in the result.