不兼容的字符编码：ASCII-8BIT和UTF-8 LIKE？＆＃39;，＆＃34;％＃{params [：search]}％＆＃34;

Question

Ruby 2.1 sqlite 3

我可以从数据库中写入和读取数据，但无法搜索。 视图中有一个搜索字段，提交时有

Encoding::CompatibilityError in AdvertisementsController
incompatible character encodings: ASCII-8BIT and UTF-8

但是日志中的参数是

{"utf8"=>"✓",
 "search"=>"essai"}

“essai”是搜索字段中的单词。

view.erb

<%= form_tag advertisements_path, method: :get do %>
  <%= text_field_tag :search, params[:search] %>
  <%= submit_tag "Search", name: nil %>
<% end %>

advertisements_controller.rb

def index
    if params[:search]
      @advertisements = Advertisement.find(:all, :conditions => [' name LIKE ? or content LIKE ?', "%#{params[:search]}%", "%#{params[:search]}%" ])
    else
      @advertisements = @advertisements.published.
        include_associations.page(params[:page])
    end
  end

怎么了？