PHP - extended __construct

Call parent::__construct() in a::__construct():

class a extends b
{
   public function __construct()
   {
       parent::__construct();
   }   

   public function validateStuff()
   {
      $this->insert_record();
   }
}

You can omit a's constructor altogether if you're not doing any a-specific stuff.

The parent __construct() method defined in class b will run automatically if you instantiate child class a, unless there is a __construct() method defined in class a.

class a extends b { 
} 

class b { 
   public function __construct() 
   { 
      echo 'In B Constructor'; 
   } 
} 

$x = new a();

If a __construct() method is defined in class a, then this overrides the use of the __construct() method in class b.... it will run instead of the class b __construct() method

class a extends b { 
   public function __construct() 
   { 
      echo 'In A Constructor'; 
   } 
} 

class b { 
   public function __construct() 
   { 
      echo 'In B Constructor'; 
   } 
} 

$x = new a();

So if your child class has a __construct() method defined, then you need to explicitly call the constructor for the parent if you want to execute that as well.

class a extends b { 
   public function __construct() 
   { 
      parent::__construct();
      echo 'In A Constructor'; 
   } 
} 

class b { 
   public function __construct() 
   { 
      echo 'In B Constructor'; 
   } 
} 

$x = new a();

I'm not sure I fully understand what you are asking, but you can call the parents construct method from the child's constructor

parent::__construct();

That's the only option I know of.