Need advice to get my logic correct in d7 - drupal

Question

Goal: Is to save information of a node which gets updated. We need to gather the node id of the node which is updated and also the user names of people who have bookmarked it.
Implementation:
I have managed to get the both this detail using flags and rules module. I made a custom module which implemented the hook to get this info.
I am getting stuck here:
Now I need to save the user name and the node id. I am still deciding if I want to use fields or the db layer.
One username can have multiple node id saved.
Now the problem is I don't know for sure how many nodes will be enough. It depends on the user. It can be 5 can be 500 or even 5000 node ids that might need to be saved for one user.
So how do I make provision for this ?
So I am stuck with the logic. How should I use the db layer or the fields in custom content type to save this ? and how should I do it ?
Please advice. I am using d7.
custom module code
/*
* Implementation of the hook_rules_action_info()
*
*/
function customvishal_rules_action_info()
{
$actions = array(
'customvishal_action_userdetail' => array(
'label' =>t('Custom function to send notifications'),
'group'=>t('Cusotm Code for sending notifications'),
'parameter'=> array(
'account'=> array(
'type'=>'user',
'label'=>t('Going to get user list'),
),
// for the node
'productdetail'=> array(
'type'=>'node',
'label'=>t('Passding the node data'),
),
)
),
);
return $actions;
}
/*
* The action function for the rules exampled hello world
*
*/
function customvishal_action_userdetail($account,$productdetail)
{
drupal_set_message(t('This user #username! has flagged it',
array('#username' => $account->mail)));
drupal_set_message(t('This node #nid has got updated',
array('#nid' => $productdetail->nid)));
// The above takes care of the node and the user information later I will put
// it in a db or something like that.
// end of the function customvishal_action_userdetail
}

Answer 1

It really seems like you should be using hook_node_update() and hook_node_insert() to for access to nodes that have just been added or updated.
If you wanted access to the node data just before it was saved, then hook_node_presave() would be the one to use.
I don't think you need presave though because you mentioned you needed the node ID, and presave does not have that for new nodes yet.
Here's a way to process new and updated nodes. The first 2 functions just hook into the right place and route the node to the 3rd function.
<?php
// hook into node inserts
function customvishal_node_insert($node) {
if ($node->type == 'mynodetype') {
customvishal_handle_data($node);
}
}
// hook into node updates
function customvishal_node_update($node) {
if ($node->type == 'mynodetype') {
customvishal_handle_data($node);
}
}
// custom handler for the nodes
function customvishal_handle_data($node) {
// load a user object of the node's author
$author = user_load($node->uid);
// now do what we need to do with $node and $user data
}
Remember you need to clear the Drupal cache for new hooks in your module to work in D7.