title: Rails Rspec allow_any_instance_of raises "does not implement" error for ActiveRecord object attributes
body: <p>I have next problem. When I try to stub instance method of ActiveRecord model with <strong><em>allow_any_instance_of</em></strong> I receive error message "Model does not implement #method", BUT if i send real request to database for create or select instance object of this model before this stub, i don't have this message and everything is ok! 
  I have same issue in console</p>
  
  <pre><code>Reloading...
  
  &gt;&gt; Search.method_defined?(:tickets_count)
  =&gt; false
  
  &gt;&gt; Search.method_defined?(:affiliate_id)
  =&gt; false
  
  &gt;&gt; Search.last
    Search Load (3.9ms)  SELECT  "searches".* FROM "searches"  ORDER BY "searches"."id" DESC LIMIT 1
  =&gt; #&lt;Search:0x007fe2aecf2900
   id: 515711,
   tickets_count: 1,
   affiliate_id: nil
  
  &gt;&gt; Search.method_defined?(:affiliate_id)
  =&gt; true
  
  &gt;&gt; Search.method_defined?(:tickets_count)
  =&gt; true
  </code></pre>
  
  <p>Could anybody explain, what the hell is going on, please?))</p>