Getting a value from select - Drupal - drupal

Question

I have a question. How to get a value from a $form['item'] so that i can use the value to filter data in form['item_2'].
Example:
For option where table looks like :
item_id item_name
1 pencile
2 book
So when i chose 2 book it will filter out data in the other form where i have table looking like :
newitem_id item_id newitem_name
1 1 hard
2 1 soft
3 2 novel
The example code :
function my_module_form($form,&$form_submit){
$form=array();
$select=db_query("SELECT * FROM {table_1}");
$options_one=array();
foreach($select as $data){
$options_one[$data ->item_id] = $data -> item_name;
}
$form['item'] = array(
'#title'=>t('Items'),
'#type' => 'select',
'#options' => $options_one,
'#required' => TRUE,
);
$temp=1;
$select = db_query("SELECT * FROM {table_2} WHERE newitem_id=:item_id",array(':item_id'=>$temp));
$options_two=array();
foreach($select as $data){
$options_two[$data ->newitem_id] = $data -> newitem_name;
}
$form['item_2'] = array(
'#title'=>t('Items'),
'#type' => 'select',
'#options' => $options_two,
'#required' => TRUE,
);
Now in the code for $temp i use number one and it gives me hard and soft values in dropdown. But how can i add the selected value from the $form['item'] to the $temp.

Answer 1

You could either use simple jQuery in your case or you could use drupal FORM API #ajax property.An array of elements whose values can control the behavior of the element with respect to the Drupal AJAX framework.AJAX (Asynchronous Javascript and XML) is a term used for dynamic communication between the browser and the server, without page reloads.You could find more details on this property here.If you find it difficult you could try the examples for developers which drupal provides shows exactly how the values in a dropdown is dependent on another drop down.
Drupal Developer examples
Using Simple Jquery(if your values just static values.If you need to take values from db,should be using jQuery+ajax)
Jsfiddle