Rails 4：在PostgreSQL中将值另存为JSON字符串对象/数组

我在“配置”表中有1列称为“ message_notification ”。我想在此列中将保存结果生成为JSON对象：

message_notification: [
  {
    "alert" : "how are you doing today?"
  },
  {
    "alert" : "where have you been today?"
  }
]

对于表格，我用

<%= simple_form_for(@configuration) do |f| %>
  Alert 1: <%= check_box_tag "configuration[message_notification][][alert]", 'how are you doing today?' %><label>Alert 1</label><br/>
  Alert 2: <%= check_box_tag "configuration[message_notification][][alert]", 'where have you been today?' %><label>Alert 2</label><br/>
  <%= f.submit %>
<% end %>

如何实现呢？

[更新]

上面的代码将解析为ruby哈希（而不是JSON）

我的控制器

@configuration.message_notification = {
  alert: params[:message][:alert]
}.to_json

结果：

message_notification: [
  {
    "alert" => "how are you doing today?"
  },
  {
    "alert" => "where have you been today?"
  }
]

[更新2]

在控制台中：

=> a = value.message_notification
=> "[{\"alert\"=>\"alert1\"}, {\"alert\"=>\"alert2\"}]"
=> puts a
=> [{"alert"=>"alert1"}, {"alert"=>"alert2"}]
=> nil