Adding Where clause in Views Query using a custom filter Handler

Question

How can I add a where clause in custom filter handler for views query.

I need to add where clause to alter views query using custom filter handler.

My code in custom filter:

class fee_management_handler_filter_payment_status extends views_handler_filter_many_to_one {
  function get_value_options() {
    $this->value_options = array('1' => 'Paid', '0' => 'Unpaid');
  }

    /**
        * Called to implement a payment status.
    */  
    function query() {  

        if filter = unpaid or 0 

        view conditions  + = ' AND pid IS NULL';    

        parent::query();
    }
}

Answer 1

function query() {
        parent::ensure_my_table(); #$this->ensure_my_table();
        $alias = $this->table . '_' . $this->view->base_table;
        $operator = ($this->value['0']) ? 'IS NOT' : 'IS';
    $this->query->add_where(0, $alias . '.pid', NULL, $operator . ' NULL');
        #debug($this->query);   
        parent::query();
    }