Loading the previous revision of a node - drupal

Question

When you get a node, how do you load the previous version (revision)?
I know how loading a revision but not how getting the previous revision number ($node->vid is the current revision).
thanks

Answer 1

Supposing that you have a node object $node, you can use the following code to get the previous revision.
$previous_vid = db_result(
db_query('SELECT MAX(vid) AS vid FROM {node_revisions} WHERE vid < %d AND nid = %d', $node->vid, $node->nid)
);
Once you have the previous revision, you can load the new node object with node_load(array('nid' => $node-nid, 'vid' => $previous_vid)).
The code should check if db_result() returns FALSE, in the case there isn't a previous revision.
To note that the field vid is global for each node; it doesn't contain the same value for different nodes.

Answer 2

Thanks all.
I found also an other solution:
$revisions = node_revision_list($node);
next($revisions);
if ($preview_key = key($revisions)) {
$preview_revision = $revisions[$preview_key];
$old_node = node_load($node->nid, $preview_revision->vid);
}
But if you have a lot of revision you get a big array.

Answer 3

If I understand what you're trying to do; you want to get the preview of the node after someone submits changes?
The preview button has its own submit handler, node_form_build_preview(). There, it creates a new node object using the data in $form_state and runs node_preview(), which returns the markup for the preview.
If you want to capture that preview when the user clicks the preview button, you'll need to use hook_form_alter to add another submit handler to the preview button:
$['form']['buttons']['preview']['#submit'][] = 'mymodule_custom_preview';
where mymodule_custom_preview is the name of your custom submit function. Take a look at node_form_build_preview() for guidance, but your submit function is going to look something like this:
function mymodule_custom_preview($form, &$form_state) {
$node = node_form_submit_build_node($form, $form_state);
$preview = node_preview($node);
}
Also take a look at node_form(), which gives you an idea of how the node form is structured. When you're all done, you're going to have code in your module that looks something like this:
function mymodule_form_alter(&$form, $form_state, $form_id) {
if (strstr($form_id, '_node_form') !== FALSE) {
$['form']['buttons']['preview']['#submit'][] = 'mymodule_custom_preview';
}
}
function mymodule_custom_preview($form, &$form_state) {
$node = node_form_submit_build_node($form, $form_state);
$preview = node_preview($node);
// Do what you will with $preview.
}