这是源代码：

 def sign_in(user)
    remember_token = User.new_remember_token
     #等效于：cookies[:remember_token] = { value:   remember_token,expires: 20.years.from_now.utc }
    cookies.permanent[:remember_token]=remember_token
    remember_token2 =User.encrypt(remember_token)
    puts ‘save remember_token1----------------->>:',remember_token2
    user.update_attribute(:remember_token , remember_token2 );
    self.current_user=user
  end

def current_user
    remember_token = User.encrypt(cookies[:remember_token])
    puts 'find remember_token3----------------->>:',remember_token
    puts 'if it find',User.find_by(remember_token: remember_token)
    @current_user||= User.find_by(remember_token: remember_token)
 end

 def User.new_remember_token
    SecureRandom.urlsafe_base64
  end

  def User.encrypt(token)
    Digest::SHA1.hexdigest(token.to_s)
  end

然后运行调用 sign_in 函数，传入一个 user：出现的结果：

save remember_token1----------------->>: aaf9c6a67eafc3f77e9e5f73bcd65f6d8f2d3948 (0.1ms) begin transaction Binary data inserted for string type on column remember_token SQL (0.5ms) UPDATE "users" SET "remember_token" = ?, "updated_at" = ? WHERE "users"."id" = 1 [["remember_token", "ac125e21202b352dbc32d654fa71794fb0b1df01"], ["updated_at", Sat, 09 Nov 2013 01:59:54 UTC +00:00]] ps：为嘛 update 的时候，remember_token 它就变了呢，泪奔啊！！！！！ (151.8ms) commit transaction User Load (0.3ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1 [["id", "1"]] Rendered users/show.html.erb within layouts/application (0.3ms) find remember_token3----------------->>: aaf9c6a67eafc3f77e9e5f73bcd65f6d8f2d3948 User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."remember_token" = 'aaf9c6a67eafc3f77e9e5f73bcd65f6d8f2d3948' LIMIT 1 if it find

注意最后一行是空的，说明没找到，google 了一下，说是编码问题，反正没解决