new nodeapi op 'delete pre' -- custom controls for modules during delete cycle

just a note that this patch will apply to both 4.6.x and HEAD. marking the version as 'cvs'. also, attached is the screenshot i mentioned above.

>>a) New features don't get added to 4.6, this would only go into HEAD.

no problem there. since many people are waiting for this feature, i'll include this patch (or a patched version of node.module) so that the functionality will be available for those that wish to begin using my module right away in 4.6.x

>>b) You're using the historic argument order to implode(), and leaving out the 2nd argument, which is not >>allowed according to the PHP docs.

attached patch corrects this.

>>Also, you don't deal with mass-deletion. This needs to be added, otherwise things might break if your >>module depends on operations being performed on deletion.

this shouldn't be necessary, as the modules have ample tools to deal w/ mass deletion themselves--as long as they can pass some kind of control stucture into the deletion cycle (so that the module knows what kind of delete operation it needs to perform). i've tested the multiple delete functionality extensively in eventrepeat.module, and it works flawlessly with this patch in place. my thinking in designing this patch was add the absolute minimum to core that allows the modules some control in the deletion process. i think this is all that they'll need as long as they're well written.

>>But, steven is right when he says you should deal with batch deletion. in node/admin you can delete a >>range of nodes at once. your patch will break that.

not true. this patch isn't involved in the actual deletion of nodes, only with allowing modules to pass in a control structure so they have the ability to initiate different kinds of deletes--this doesn't interfere w/ the admin batch delete functionality at all. admin batch delete has it's own custom delete function, and this hook will not be called during it.

here is a detailed use case for this patch, so that the flow can be seen more clearly:

in eventrepeat.module, i have a need to be able to give the user a choice to delete entire repeat sequences, or just the current node. this needs to be decided at time of deletion, and i want to give them three choices:

'this occurance'
'this occurance and all future occurances' (which deletes from the date of the selected node forward)
'all occurances' (which deletes from today's date forward)

prior to this patch, there was no way that my module could inject this kind of control structure into the deletion process. here's the hook i put into eventrepeat.module to take advantage of the new feature provided by this patch:

function eventrepeat_delete_confirm($node) {
if (variable_get('event_nodeapi_'. $node->type, 'never') != 'never' &&
variable_get('eventrepeat_nodeapi_'. $node->type, 0) == 1) {

if ($node->eventrepeat_rid) {
$form .= form_hidden('eventrepeat_rid', $node->eventrepeat_rid);
$options = array(
'this' => t('This occurance only'),
'future' => t('This occurance and all future occurances'),
'all' => t('All occurances')
);
$form .= form_radios('Repeat event--delete the following:', 'eventrepeat_delete_type', 'this', $options, $description =
t('\'This occurance and all future occurances\' will delete repeat events from the date of the selected node forward,
\'All occurances\' will delete repeat events from today\'s date forward.'),
$required = FALSE, $attributes = NULL);
}
return $form;
}
}

this injects the id of the repeat sequence and the control structure i detailed above into the delete confirmation screen (i do some checks at the top to make sure that this data is only injected for nodes that are in a repeat sequence). now, when the user clicks 'Delete', the info i injected is available as $_POST data. since the user clicked delete, drupal processes the deletion of the node, and eventually during that process eventrepeat_nodeapi is called, at which point the module grabs the info it needs from $_POST. if, for example, the user selected 'all occurances', the module then calls it's own custom delete function to handle that process. simply put, the guts of that process is grabbing all the nids that need to be deleted, and calling node_delete for each one (in this case i pass in the confimation setting as well to node_delete, to automate the process). node_delete takes care of all the deletion dirty work for each node. the only tricky part is making sure that my custom delete function isn't called from eventrepeat_nodeapi multiple times (b/c that's called multiple times in a multiple delete)--i take care of this by unsetting the injected $_POST data when my custom delete function is called. works beautifully... :)

>>And furthermore, I would like to see a good piece of documentation on how to use this.

hopefully the above example makes usage clear, but i'd be happy to write up more doc if needed.

>>From what you have coded it seems the hook must return an array. Why not a straing?

the hook returns an html string which is the form data that will be injected into the confirmation screen

>>You concenate arrays with nothin ('') which IMHO is bad PHP. But I guess you have good reasons for >>returning a string.

these steps are necessary, because:

#1 module_invoke_all returns an array, and each element of the array is an html string that i described above. if multiple modules return form data to be injected into the confirmation screen, this array will have multiple elements

#2 the $extra argument in theme confirm needs to be passed in as a string, so i implode the array. it's best to include the 'glue' argument in implode (according to PHP documentation), but i don't want a seperator--i just want to turn the array into a string. therefore i insert an empty string as the 'glue'.

>>2: the fact that both Steven and I misread your patch shows that the use of this hook needs
>>clarification. I am not sure how the hooks at drupaldocs are documented, but it really needs to show up
>>there, with details about what to returns and what to pass along. Also some clarification about when
>>this hook is called is important (for that caused the confusion at #1)

i definitely agree. it's usage confused me in the beginning and i wrote it... ;)

if the patch gets committed, i'm happy to write supporting documentation for hook_delete_confirm and post it whereever it needs to go

ok, based on several discussions with core developers, i've expanded the functionality so that mods can inject info into the admin mass delete cycle as well. for single node deletions, the patch allows for multiple modules to inject info into the confirmation screen. for admin mass deletions the same capability exists, plus modules can also inject data for multiple nodes. for the admin part of the hook, i also cleaned up the code that prints the confirmation screen--removing some unnecessary database queries and putting the list of nodes to be deleted into a theme_item_list. because of the extra database queries i removed, i think performance will be about the same even with the new functionality. this patch introduces a very handy functionality, and i've already found use for it in two of the mods i'm developing... :) not only can it inject control structures to enable mods to handle different types of multiple deletions (which i use in eventrepeat.module), but it can also be used to inject custom module messages into the delete cycle (ex., in signup.module, i use it to warn users when they're about to delete a node that users are signed up for!)

for the module developer, this hook takes one argument, which is an array of nids to be deleted, and returns an array, the elements of which are also an array, with each key being the nid for which to inject the data, and the corresponding value is the data to be injected. (the array nesting was necessary because of the way module_invoke_all returns it's results. this approach returns each mod's custom injection data in it's own array--very flexible!)

you can see this hook in action here--username 'test' password 'drupal'. please also note that i didn't spend much time on working out the list theming, so we can clean that up later if it's not to everyone's liking!

that last link to the test site was no good.

try here--username 'test' password 'drupal'

also, i'll post some screenshots of the hook in action, and write up some better doc in the next day or two...

attached are some screenshots of what this hook can do.

after some more talks w/ other developers, it seems as though this functionality may fit better in hook_nodeapi, as a 'delete confirm' case. this seems to make sense b/c all modules have the option to inject data into any of the nodes that are being deleted. i'm happy to modify the patch in this case, but there is one catch that i wanted to get some opinions on before i dive in...

in order for this hook to be supported in the admin batch delete, it's necessary to pass an array of nids to the module hook, so that the module can decide which nids to inject data into. the problem is, hook_nodeapi doesn't currently have an available argument where that can be passed in. what does everybody think about the idea of adding an $extra argument? the hook would then look like:

hook_nodeapi(&$node, $op, $teaser = NULL, $page = NULL, $extra = NULL)

attached is module developer's documentation for this hook. If the code gets put into nodeapi as i mentioned above, i can modify this documentation accordingly.

after further irc discussions w/ chx, i've rewritten this hook to live in nodeapi, and added a really cool extra feature... :)

now modules can actually prevent deletion of a node by explicitly returning a value of FALSE. on a single node deletion, the user will be bounced back to the node/edit screen, and in batch deletions, the node will be removed from the batch delete queue prior to the confirmation screen. i left it up to module developers to drupal_set_message and tell their users what happened... :)

couple of things about this new approach:

1. it's less efficient than the old approach for batch deletions, because now node_load and node_invoke_nodeapi get called for each node in the batch, as opposed to the old way which just made one call for all nodes. however...

2. it now lives in nodeapi, where i believe it belongs, and

3. the implementation for module developers is now way, way easier and less complicated.

also, from an efficiency standpoint, i was able to completely remove all database queries from the confirm screen code in admin batch delete (the current approach queries the database once for each node in the batch, which i thought was inefficient). so i don't think the overall performance is going to be much different.

i'll post module developer code for this new version shortly. outside of the delete prevention functionality, the patch does the same thing as before--so the screenshots i posted above are still relevant.

new module developer documentation for the nodeapi version of this patch attached.

per chx's suggestions, changed node_load to node_load($nid), and renamed the nodeapi $op to 'delete pre'. also double-checked the coding style. unless anybody catches something else, i think this baby is ready to go!

Ber: btw, the name is Chad... :)

minor cleanup. just adding a comment line to clear up potential confusion--no functional changes

...and...

updated module developer doc for the latest version of the patch

the updated patch can be seen in action here

i've tested this patch extensively w/ no problems--works exactly as advertised. code has undergone review and several revisions, and is solid. developer feedback seems to indicate it's a desirable piece of functionality. switching to commit status...

Cleaned up the pass by reference stuff, and doubled checked coding style. Mass delete changes should be fine--none of the module-specific data needs to be passed to node_delete, as the mods can grab whatever data that's posted from the confirm screen (which is the same way that node delete get it's confirmation info). Just to be clear, there are two steps in the deletion cycle, and the module developer can make use of this functionality in both steps:

1. The confirmation step: the patch allows modules to inject data into the confirmation screen, and/or (under extreme cases) completely cancel the deletion of the node. Use cases for the injected data could be:
   • Warning message: ex. 'This event has X users signed up for it!' This allows relevant information to appear on the confirmation screen, instead of just the rather uninformative 'Are you sure you want to delete this?' blurb.
   • Control structure: ex, 'Delete this occurance', 'Delete all occurances'. In this instance, mods that need to get information from the user about things they'll do during the deletion cycle (like mass deletes in eventrepeat) have a way to get it! This is not possible with the current delete structure in core.
2. The deletion step: if a mod has passed in a control structure, it is available in $_POST during the actual deletion of the node. When node_delete invokes the nodeapi 'delete' op, then the mod can grab the $_POST data and perform any operations it needs. In the case of eventrepeat, I use it to perform mass deletes on other nodes in the repeat sequence.

that last patch seems to be malformed--here's a working one...

one more minor code change. it should be theme('item_list', $list), and not theme_item_list($list)...

this functionality will be included in the forthcoming undo functionality located here