与Ruby、Redis和Ohm的多对多关系

Question

我正在尝试使用Ohm在Redis中创建多对多关系。例如，我将Book和Author模型定义如下：

class Book < Ohm::Model
  attribute :title
  set :authors, Author
end

class Author < Ohm::Model
  attribute :last_name
  attribute :first_name
  set :books, Book
end

我想要做的是利用Ohm的索引功能来进行查找，例如：

require 'test_helper'

class ManyToManyRelationshipTest < ActiveSupport::TestCase

  setup do
    @dave_thomas = FactoryGirl.build(:dave_thomas)
    @andy_hunt = FactoryGirl.build(:andy_hunt)
    @chad_fowler = FactoryGirl.build(:chad_fowler)

    @pick_axe = FactoryGirl.build(:pick_axe)
    @pick_axe.authors << @dave_thomas 
    @pick_axe.authors << @andy_hunt
    @pick_axe.authors << @chad_fowler

    @thinking_and_learning = FactoryGirl.build(:pragmatic_thinking_and_learning)
    @thinking_and_learning.authors << @andy_hunt
  end

  test "find a Book by Author" do
    assert Book.find(:author_id => @andy_hunt.id).include?(@pick_axe)
    assert Book.find(:author_id => @andy_hunt.id).include?(@thinking_and_learning)
  end

  test "find Authors by Book" do
    assert Author.find(:book_id => @pick_axe.id).include?(@dave_thomas)
    assert Author.find(:book_id => @pick_axe.id).include?(@andy_hunt)
    assert Author.find(:book_id => @pick_axe.id).include?(@chad_fowler)
  end
end

使用上面的代码，我得到了以下异常: Ohm::Model::IndexNotFound: IndexNotFound: Index :author_id not found。(当试图查找给定作者的书籍时)

我尝试构建自定义索引，如下所示：http://ohm.keyvalue.org/examples/tagging.html，这里：http://pinoyrb.org/ruby/ohm-inside-tricks

不幸的是，看起来索引是在第一次创建模型时构建的，这意味着集合是空的(因为，如果我理解正确的话，集合在Ohm中是不可用的，直到模型被分配了一个ID)。

非常感谢大家的帮助和建议！

Answer 1

这种情况下的解决方案不那么自动化：

require "ohm"

class Book < Ohm::Model
  attr_accessor :authors

  attribute :title

  index :authors
end

class Author < Ohm::Model
  attribute :name
end

###

require "test/unit"

class BooksTest < Test::Unit::TestCase
  def test_books_by_author
    dave = Author.create(name: "Dave")
    andy = Author.create(name: "Andy")
    dhh = Author.create(name: "DHH")

    pickaxe = Book.create(title: "Pickaxe", authors: [dave.id, andy.id])

    assert_equal pickaxe, Book.find(authors: dave.id).first
    assert_equal pickaxe, Book.find(authors: andy.id).first

    assert_equal nil, Book.find(authors: dhh.id).first
  end
end

合乎道理?