ruby on rails - How to do inheritance between models and ActiveRecord::Base? -

I have Rails on Rails and two models using Ruby on the project:

  Class A & lt; ActiveRecord :: Base Attr_accessible: Name Valid: Name ,: Attendance = & gt; True end class B & lt; An Attr_accessible: Age is Valid: Age, Attendance = & gt; True end   
 In my a_spec.rb I can see it:  
  it should be invalid 'do @ a.should_not be_valid end   
 But I can not see this in my B_SPCRB:  
  this should be 'invalid' @b.should_not be_valid end   
 And I get a fault error:  
 
 1) B should have a valid failure / error: @B.Sold_NetB_WalliedNumber Method: Undefined method # code for  age '& lt; B Id: zero, name: zero, created_at: zero, updated: zero> '  
 Anyone can help me fix this? # ./spec/models/b_spec.rb:6:in  
 
 
 Rail generally does not have a relationship like this.  
 Unless you have a really good reason, all of your models should be inherited from ActiveRecord :: Base  
. You can add a table type to the model, You can use a single table succession (STI) for.  
 On more active records