使用text存储hash类型的数据 Use text filed to store the hash map

在component表里用text类型的字段存储hash数据

（1）新建字段 ，这是migration的内容

class AddHintsToComponents < ActiveRecord::Migration[5.0]
  def change
    add_column :components, :hints, :text
  end
end

（2）controller

  def update
    if @component.update!(component_params)
      redirect_to @component, notice: 'Component was successfully updated.'
    else
      render :error
    end
  end 

    def component_params
      params.require(:component).permit(:release_id,
                                        :remark, component_ids: [], hints: [:left, :mid, :right])
    end

（3）model

class Component < ApplicationRecord
  serialize :hints

  def after_initialize
      self.hints ||= {}
  end

（4）_component.html.erb

  <td>
    left:<%= component.hints["left"] %> |
    mid:<%= component.hints["mid"] %> |
    right:<%= component.hints["right"] %>
  </td

（5）_form.html.erb

  <%= f.fields_for :hints do |h| %>
    <div class="form-group">
      <%= f.label 'hints left', class: 'col-sm-2 control-label' %>
      <div class="col-sm-4">
        <%= h.text_field :left, class: 'form-control',
          value: (@component.hints && @component.hints.key?("left") ? @component.hints["left"] : "") %>
      </div>
    </div>

    <div class="form-group">
      <%= f.label 'hints mid', class: 'col-sm-2 control-label' %>
      <div class="col-sm-4">
        <%= h.text_field :mid, class: 'form-control',
          value: (@component.hints && @component.hints.key?("mid") ? @component.hints["mid"] : "") %>
      </div>
    </div>

    <div class="form-group">
      <%= f.label 'hints right', class: 'col-sm-2 control-label' %>
      <div class="col-sm-4">
        <%= h.text_field :right, class: 'form-control',
          value: (@component.hints && @component.hints.key?("right") ? @component.hints["right"] : "") %>
      </div>
    </div>
  <% end %>

参考资料

http://vladexologija.blogspot.com/2012/12/rails-attribute-serialization_18.html

http://guides.rubyonrails.org/action_controller_overview.html#strong-parameters