注意：代码未测试。
你真的应该 hall_of_residence_id 作为外键）：

# == Schema Information

# 

# Table name: residence_staffs

# 

# id                                :integer          not null, primary key

# first_name                        :string

# hall_of_residence_id              :integer

# position                          :string

# created_at                        :datetime         not null

# updated_at                        :datetime         not null

# 

class ResidenceStaff < ApplicationRecord
  validates :first_name, presence: true
  belongs_to :hall_of_residence

  class << self

    def managers
      where(position: 'manager')
    end

  end
end

以及：

# == Schema Information

# 

# Table name: hall_of_residences

# 

# id                                :integer          not null, primary key

# name                              :string

# created_at                        :datetime         not null

# updated_at                        :datetime         not null

# 

class HallOfResidence < ApplicationRecord
  has_many :residence_staffs
end

看起来你应该能够做一些类似的事情（参见指南中关于 includes ):

class HomeController < ApplicationController

  def index
    @residence_staffs = ResidenceStaff.all
    @residence_staff_managers = ResidenceStaff.managers.includes(:hall_of_residence)
  end

end

以及：

<h1>Title</h1>

<div>
  <% @residence_staff_managers.each do |residence_staff| %>
    <%= residence_staff.first_name>
    <%= residence_staff.hall_of_residence.name >
  <% end %>
</div>