title: laravel, how can I add extra attribute to model?
body: <p>I have a <code>product</code> table and a <code>sub_product</code> table.</p>
  
  <p>In <code>product</code> table there are many global field like <code>name</code> and <code>cat_id</code> .
  In <code>sub_product</code> table there are <code>product_id</code>, <code>color</code> and <code>Price</code></p>
  
  <p>Now I want add a filed only to <code>product</code> laravel model(collection) that give me minimum <code>price</code> for each <code>product</code> from<code>sub_product</code>. how can I do that?</p>