Dynamic ajax category child dropdown

Hi i need some help on how can i post selected variable from one dynamic dropdown to second one with ajax.
Here is my code and i need some help on how can i accomplish this.
Thank you.

//Dynamic category dropdown
add_filter("gform_pre_render_2", "monitor_single_dropdown");
function monitor_single_dropdown($form){

	global $wpdb;
	$nomos_table = $wpdb->prefix . 'nomous';
	$wp_nomos_search = $wpdb->get_results("SELECT nomos_ID, nomos_Title FROM $nomos_table ORDER BY nomos_ID ASC");

	//Creating drop down item array.
	$items = array();

	//Adding initial blank value.
	//$items[] = array("text" => "", "value" => "");

	 //Adding dimos titles to the items array
	foreach ( $wp_nomos_search as $nomostitle ){
	$is_selected = $nomostitle->nomos_Title == "Test" ? true : false;
		$items[] = array("value" => $nomostitle->nomos_ID, "text" => $nomostitle->nomos_Title, "isSelected"=> $is_selected);
	}

	//Adding other... item
	//$items[] = array("text" => "Other...", "value" => "other");

	 //Adding items to field id 28
	    foreach($form["fields"] as &$field)

	        if($field["id"] == 28){
	            $field["type"] = "select";
	            $field["choices"] = $items;
	        }

?>
<script type="text/javascript">

jQuery(document).ready(function(){

	jQuery('#input_2_28').change(function(){
			var mainCat=jQuery('#input_2_28').val();

			// call ajax
			 jQuery("#input_2_30").empty();
				jQuery.ajax({
					url:"<?php bloginfo( 'wpurl' ); ?>/wp-admin/admin-ajax.php",
					type:'POST',
				    data:'action=monitor_children_dropdown&main_catid=' + mainCat,

					 success:function(results)
						 {
	    	//	alert(results);
		 //   jQuery("#input_2_30").append(results);
								}
						   });
				  }
							);

});
</script>

<?php
return $form;
}

add_filter("gform_pre_render_2", "monitor_children_dropdown");

function monitor_children_dropdown($form) {
$parentCat=$_POST['main_catid'];

global $wpdb;
$dimoi_table = $wpdb->prefix . 'dimoi'; 

$wp_dimostitle_search = $wpdb->get_results("SELECT dimos_ID, dimos_Title FROM $dimoi_table WHERE nomos_ID=$parentCat ORDER BY dimos_ID ASC");

//Creating drop down item array.
$items = array();

//Adding initial blank value.
//$items[] = array("text" => "", "value" => "");

 //Adding dimos titles to the items array
foreach ( $wp_dimostitle_search as $dimostitle ){
$is_selected = $dimostitle->dimos_Title == "Test" ? true : false;
	$items[] = array("value" => $dimostitle->dimos_Title, "text" => $dimostitle->dimos_Title, "isSelected"=> $is_selected);
}

//Adding other... item
$items[] = array("text" => "Other...", "value" => "other");

 //Adding items to field id 30
    foreach($form["fields"] as &$field)

        if($field["id"] == 30){
            $field["type"] = "select";
            $field["choices"] = $items;
        }

    return $form;

//return the result to the ajax post
die();
}

add_action( 'wp_ajax_nopriv_monitor_children_dropdown', 'monitor_children_dropdown'); //keep for people who allow post before registration
add_action( 'wp_ajax_monitor_children_dropdown', 'monitor_children_dropdown');

Hi Stav,
First of all thanks for your code. Putting table names and re-writing the above code:

CREATE TABLE wp_cms_5_geo_COUNTRY (
   country_id INT NOT NULL AUTO_INCREMENT,
   country_name VARCHAR(200) NOT NULL,
   PRIMARY KEY ( country_id )
);
INSERT INTO wp_cms_5_geo_COUNTRY VALUES (1, 'India'),(2, 'America'),(3, 'Africa');

CREATE TABLE wp_cms_5_geo_STATES (
   state_id INT NOT NULL AUTO_INCREMENT,
   state_name VARCHAR(200) NOT NULL,
   country_id INT,
   PRIMARY KEY ( state_id )
);
INSERT INTO wp_cms_5_geo_STATES VALUES (1, 'Rajasthan', 1),(2, 'Delhi', 1),(3, 'Punjab', 1),(4, 'Washington DC', 2),(5, 'New York', 2),(6, 'Cape Town', 3);

<?php
//Dynamic category dropdown
add_filter("gform_pre_render_1", "monitor_single_dropdown");
function monitor_single_dropdown($form){

	global $wpdb;
	$country_table = $wpdb->prefix . 'geo_COUNTRY';
	$wp_nomos_search = $wpdb->get_results("SELECT country_ID, country_Name FROM $country_table ORDER BY country_ID ASC");

	//Creating drop down item array.
	$items = array();

	//Adding nomos to the items array
	foreach ( $wp_nomos_search as $nomos ){
	$is_selected = $nomos->country_Name == "Rendered Title" ? true : false;
	$items[] = array("value" => $nomos->country_ID, "text" => $nomos->country_Name, "isSelected"=> $is_selected);
	}

    //Adding other... item
	$items[] = array("text" => "Other...", "value" => "0");

	 //Adding items to field id 4
	    foreach($form["fields"] as &$field)

	        if($field["id"] == 4){
	            $field["type"] = "select";
	            $field["choices"] = $items;
}

?>
<script type="text/javascript">

jQuery(document).ready(function(){

	jQuery('#input_1_4').change(function(){
			var mainCat=jQuery('#input_1_4').val();

			// call ajax
			 jQuery("#input_1_5").empty();
				jQuery.ajax({
					url:"<?php bloginfo( 'wpurl' ); ?>/wp-admin/admin-ajax.php",
					type:'POST',
				    data:'action=monitor_children_dropdown&main_catid=' + mainCat,

					 success:function(results)
						 {
	    	//	alert(results);
		       jQuery("#input_1_5").append(results);
								}
						   });
				  }
			);
});

</script>

<?php
return $form;
}

//ajax callback function
function monitor_children_dropdown() {
if(isset($_POST['main_catid'])) {

$parentCat=$_POST['main_catid'];
global $wpdb;
$states_table = $wpdb->prefix . 'geo_STATES';
$wp_dimos_search = $wpdb->get_results("SELECT state_ID, state_Name FROM $states_table WHERE country_ID=$parentCat ORDER BY state_ID ASC");

              //Creating drop down item.
			  foreach ($wp_dimos_search as $dimos) {
				$option .= '<option value="'.$dimos->state_ID.'">';
				$option .= $dimos->state_Name;
				$option .= '</option>';
			  }
               //	Adding other... item
			  echo '<option value="0" selected="selected">Select...</option>'.$option;
	  die();
 } // end if
}

add_action( 'wp_ajax_nopriv_monitor_children_dropdown', 'monitor_children_dropdown'); //keep for people who allow post before registration
add_action( 'wp_ajax_monitor_children_dropdown', 'monitor_children_dropdown');
?>

Would you post link of where this is being used? I'd like to see it in action to determine if it fits what I need (displaying one post category only in dropdown). thanks.

Hi Leonardo,

Did you ever get a third level working? Please let me know.

Thanks,
John