Rails:仅使用连接表进行多对多展平 [英] Rails: Many-to-many flattening with only the join table

问题描述

我有一个模型对象，它以多对多关系链接到国家/地区列表.这些国家/地区以它们的 ISO 3166 alpha-2 代码为键.

I have a model object which is linked to a list of countries in a many-to-many relationship. The countries are keyed by their ISO 3166 alpha-2 codes.

我想要完成的事情是保存使用 Country 类和表，并且只有我的对象具有 object.countries 形式的访问器，它将返回一个数组字符串，例如:["IL", "US", "IT", ... ].

The thing I'd like to accomplish is to save to use of a Country class and table, and only have my object have an accessor in the form of object.countries that will return an array of strings, e.g: ["IL", "US", "IT", ... ].

本质上，一种只有连接表的 has_and_belongs_to_many 操作.这可能吗?

Essentially, a sort of has_and_belongs_to_many action with only the join table. Is this possible?

在国家/地区列表的情况下是否有最佳做法?

Is there a best practice in the case of country lists?

推荐答案

这就是我最终解决的方法，我在数据库中创建了一个国家表，因为我更喜欢 HABTM 关系.

This is how I eventually solved it, I created a countries table in the database, as I preferred a HABTM relationship.

但为了简化事情，我覆盖了集合上的 << 操作符，这样我就可以将国家代码作为字符串或字符串数​​组推送 (object.country <<'IL'):

But to simplify things, I overrode the << operator on the collection so I could just push country codes as string or array of strings (object.country << 'IL'):

has_and_belongs_to_many(:countries) do
  def <<(country)
    if [*country].all? {|c| c.is_a?(String) }

      countries = Country.where(:code => country)
      concat(*countries)

    else

      concat(country)

    end
  end
end

您可能会认出 此处.
传递 concat(*countries) 还可以让 Rails 在单个事务中插入所有行，这是一个很好的奖励.

You might recognize that [*...] trick from here.
Passing concat(*countries) also makes Rails insert all the rows in a single transaction, which is a nice bonus.

并添加了一个函数来向国家/地区返回代码的简化哈希:

And added a function to return a simplified hash of codes to countries:

def countries_hash
  return self.countries.map {|c| { c.code => c.name }}.inject({}) {|hash, elem| hash.merge!(elem)}
end

当然，我很乐意听到任何建议.

Of course I'd be glad to hear any suggestions.

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