ruby-on-rails-3 – 错误：运算符不存在：字符变化=整数

<% unless @user.hotels.empty? %>
  <% @user.hotels.each do |hotel| %>
    <%= "#{hotel.description} #{hotel.name} in #{hotel.city},#{hotel.country}" %><br />
  <% end %>
<% end %>

这是从heroku日志：

ActionView::Template::Error (PGError: ERROR:  operator does not exist: character varying = integer
LINE 1: SELECT "hotels".* FROM "hotels" WHERE ("hotels".user_id = 1)
                                                                ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
: SELECT "hotels".* FROM "hotels" WHERE ("hotels".user_id = 1)):

@ user.hotels.empty？创建错误.我知道,sqlite是相当原谅,但PostgreSQL不是.这是酒店型号的外键：user_id：integer

Heroku说：

Make sure the operator is adequate for the data type. ActiveRecord does this automatically when you use an interpolated condition form.

Array conditions:
:conditions => ['column1 = ? AND column2 = ?',value1,value2]

Hash conditions:
:conditions => { :column1 => value1,:column2 => value2 }

迁移如下所示：

class CreateHotels < ActiveRecord::Migration
  def self.up
    create_table :hotels do |t|
      t.string :name
      t.string :vanity_url
      t.integer :user_id
      ....