正在加载与活动记录模型关联的外部数据

ActiveRecord 使用与每个对象相关的外部数据进行建模,我正在尝试找出一种干净、高效的方法来实现这一点。

class State < ActiveRecord::Base
  def counties
    @counties ||= fetch_external_data(state: name)['counties']
  end
end

State.find_by_name('Alabama').counties

但是如果我有一个对象集合(通过 ActiveRecord::Relation ),则这将导致对该外部数据源的N+1查询。

State.where(name: %w[Alabama Georgia]).map(&:counties)

理想情况下,我希望从外部数据源加载所有数据,然后 counties 实例方法从这个“共享”对象访问数据。我可以使用一个类方法:

class State < ActiveRecord::Base

  attr_accessor :counties

  def self.with_counties
    # Get external data for all states in our scope
    counties = fetch_external_data(states: pluck(:name))

    # Group by the state
    counties_by_state = counties.group_by { |c| c['state'] }

    # Now hydrate all of the state models and set the counties
    all.map do |state|
      state.counties = counties_by_state.dig(state.name, 'counties')
    end
  end
end

虽然这是可能的,但它使我无法在使用后进一步链接作用域 State.where(name: %w[Alabama Georgia]).with_counties

ActiveRecord::关系 当记录被冻结时可以访问的对象)?如果我有一个表示这个外部数据接口的类,那么我可以在这个类上定义一些方法来让它工作吗 State.includes(:counties) State.eager_load(:counties) ?