While editing a node I've printed the dsm($form) in hook_form_alter and in the dsm array I see the following values:

form_id (Array, 3 elements)

    #type (String, 6 characters ) hidden
    #value (String, 14 characters ) unit_node_form
    #id (String, 19 characters ) edit-unit-node-form


This node's machine name is "unit" I want to know what is the difference between #value and #id values.

I want to catch form alter of only this node while editing it.

1 Answer 1


Typically you would use a check on $form_id to make sure your hook_form_alter would only apply the specific form. A node editing form is normally only present on edit pages, so it would only apply to edit pages as the form is not displayed anywhere else.

Don't forget that hook_form_alter is called on all forms, so you need to check for the some values to not apply it to all forms. Usually this is the form_id.

To check for a specific form you would use:

* Implementation of HOOK_form_alter()
function MYMODULE_form_alter(&$form, $form_state, $form_id) {

  if ($form_id == 'unit_node_form') {



This can be helpful if you modify multiple forms in one module. If you prefer not to do that you should maybe use hook_form_FORM_ID_alter() to modify only a specific form.

Checking the form api $form_id is defined as:

String representing the name of the form itself. Typically this is the name of the function that generated the form.

The question this throws up now is:

Is $form_id defined from


or from


Both of which give the same results. So unfortunately I can not directly give you an answer, other than that the form will only display on edit pages, so using $form_id seems to be standard proceedure.

  • Thanks but my question is whether form id of "unit_node_form" specifies the unit node form while in edit mode? That is I want to change the form field only in edit mode. To be sure do I also need to check for edit-unit-node-form ?
    – AgA
    Dec 6, 2011 at 12:55
  • I am confused! When you say 'edit mode', do you mean when an already existing node is edited as opposed to when a new node is created? Please clarify.
    – tecjam
    Dec 6, 2011 at 13:13
  • In both the cases if node is new or being re-edited. I don't want the user to enter any title.
    – AgA
    Dec 6, 2011 at 13:22
  • In that case I have already provided you the answer. The node edit form will only be shown on the edit or create page. Nowhere else unless you have a really, really strange setup. so using $form_id will work perfectly.
    – tecjam
    Dec 6, 2011 at 13:27
  • 1
    Yes, that is correct. The form is only shown on the edit and create page. If you would like to check to see the form_id to make sure it is right for every form shown anywhere, create a basic module - add mymodule_form_alter function - like above - but before checking the form id add this line dsm($form_id); and it will show your form_id on any form in the message area. that way you can double check and make sure you're applying your function to the correct form_id.
    – tecjam
    Dec 6, 2011 at 13:39

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