Editing node throws "Undefined property" stdClass::$nid in hook_node_prepare()

These notice is harmless. The title or theme cannot be the reason. The node object need to have a nid property.

This is very strange and needs more info. The $node object need to be dumped for a review.

This happens only on new nodes, isn't it? Not with nodes that have been saved and are edited again.

I cannot repro this issue.

Please add a line in the function in "linkchecker.module" file, repro the issue step by step (including all URLs), until you see the notice and let me know if there is a NID. Ist must be there... please attach the array.

function linkchecker_node_prepare($node) {
  // If you have devel installed
  krumo($node);
  // or if not.
  var_dump($node);

Can you confirm the issue happens only with faq pages? I have never seen this with basic page and articles... Is this a book type or something from the faq module? This could be a major bug in the faq module.

Let's move to FAQ module queue, so we can find out the source of this bug and why this modules clutter the node object API structure many module rely on. The maintainers need to fix these bug. If it's FAQ_Ask module, feel free to move again and set the correct version you are using.

Silly question: Is this problem still there also in the 7.x-1.x-dev version?
Could you try and uninstall FAQ-Ask (or at least disable it) and see if that has any effect?

How does the #4 array look like with the one or the other module disabled?

I bet this is something in the cross-section between FAQ Ask module and the Link Checker module. I'll have a look at this issue and see if I'm able to recreate.

I have made several attempts to recreate this problem without luck. Could you please provide a step-by-step instruction to this issue from a clean drupal-install?

@Stenjo: are you changing the node object structure? If you do, this is the bug.

same issue here.

With reference to #1, aparently the node need not have a nid property when the node is not created yet - wich is the case for the question form.
From the API reference on hook_node_prepare we can read:

Drupal 7 hook_node_prepare($node)
Act on a node object about to be shown on the add/edit form.

The Ask a question form is a modified node add form and hook_node_prepare() is called when the line

$form = node_add('faq');

is run in the faq_ask_a_question_blockform()
I'd say the Link Checker code should not rely entirely on the presence of nid in the node object.

You may misunderstood something. Below code makes sure that this code (SQL request) runs only on node Edit forms and never on Add node forms where an NID does not exists.

/**
 * Implements hook_node_prepare().
 */
function linkchecker_node_prepare($node) {
  // Node edit tab is viewed.
  if (arg(0) == 'node' && is_numeric(arg(1)) && arg(2) == 'edit') {
...

The problem is in the faq node object that is missing $node->nid. Every node module rely on this object structure. You cannot move the NID property anywhere else just for the reason that you like it. If you change the structure, the faq ask module becomes incompatible with every node module.

See #4 for the dumped object of the broken structure, please. It looks like you moved the $node->nid property to $node->book['nid']. $node->nid does not exist. This is the bug.

nid is a well known reference in the node table for all node objects. Without such a reference we cannot save data in a relational database.

http://api.drupal.org/api/drupal/modules%21node%21node.module/function/n... is calling the module_invoke_all('node_prepare', $node); and also requires an $node->nid to be set or the conditions inside these core function will fail.

I'm personally not able to repro the issue with FAQ and Ask FAQ module and the Ask FAQ block. I'm using Seven theme.

The reporters should provide a step by step instruction how we are able to repro the issue.

In #19 the code you are referring to assumes we are dealing with only one form - but in fact we are dealing with two of them: One that is being displayed and retrieved based on the node in the database. This is also the one you get when parsing the path the way the code you refer to is written now. The faq_ask form is located in a block and also loads a node edit form, but this node is not created yet, therefore it is a node add form - without the nid property in the node object. Nor should it be. The nid property is added to the node object upon creation in the database.
The faq_ask code does not at any point remove or move the nid property. Nether does it call the node_object_prepare();
The Link Checker hook_node_prepare() implementation should not be dependant on the presence of a nid property and should neither assume only one form is being loaded. In this case hook is called twice when browsing to a node/$nid/edit page when the Ask a question block is enabled:

• once for the node being edited
• once for the node create form in the Ask a question block

Modifying the code to something like this:

/**
* Implements hook_node_prepare().
*/
function linkchecker_node_prepare($node) {
  // Node edit tab is viewed.
  if (arg(0) == 'node' && is_numeric(arg(1)) && arg(2) == 'edit' && isset($node->nid)) {
...

should take care of it all.

Patch attached.

Ok, now I got it. With Overlay enabled you will not see the warning.

Thanks for these simple patch.

D6: http://drupalcode.org/project/linkchecker.git/commit/1866cf1
D7: http://drupalcode.org/project/linkchecker.git/commit/4a22c68