Entity Metadata Wrapper Save VS Node Save when invoked from hook_node_insert

Question

Can somebody shine a light into the difference of the two, in terms of their interaction with database when hook_node_insert() is invoked? The documentation explains that

Note that when this hook is invoked, the changes have not yet been written to the database, because a database transaction is still in progress. The transaction is not finalized until the save operation is entirely completed and node_save() goes out of scope.

In fact, when I tried doing node_save($node), it will give me an error.

However, if I was doing it this way,

$nodeWrapper = entity_metadata_wrapper('node', node_load($node->nid));
$nodeWrapper->title->set(t("Saved by Entity Save"));
$nodeWrapper->save();

It works just fine. Has the new node being committed into the database after the $nodeWrapper->save() was executed?

Answer 1

Essentially, there really isn't much difference between node_save() and the save() method of the entity metadata wrapper. Neither should however be used to save the node passed in as the argument to hook_node_insert().

The argument is passed by reference (since it's an object and all objects are passed by reference in later PHP versions), and any changes you make to it will be included when the node is saved by Drupal just after it's done calling the hook implementation.

Trying to manually save the same node again could trigger endless recursion into your hook_node_insert() implementation.

Just alter the node object as you see fit (setting the title in this case, though that is not a translatable string, so replace t() with check_plain()) and do nothing more.

If you need to do more complex alterations, the entity metadata wrapper could come in handy, but you must remember that any alterations you want to have saved must be performed on the node instance passed as a reference to hook_node_insert(). This means you can't node_load($node->nid) here first, since that would actually just create a new node object with data that's already in the database. If you do manage to save that node copy without ending up in a recursion loop, it would either mean that the node save already in progress - the reason hook_node_insert() was originally called - overwrites any changes you made, or fails because the new node to be saved already exists.

Instead, pass the $node argument to entity_metadata_wrapper() directly and the wrapper will be able to alter the correct node object for you, but remember to not call save() on the wrapper!

Answer 2

Calling node_save() from inside a hook_node_insert() implementation is error prone and should only be done with sufficient condition checks as to not provoke function nesting.

When you call node_save() coming from an insert operation and saving the $node object that already has an nid, then this call of node_save probably creates an update operation, which might result in strange errors. I don't fully follow the information flow here, but I would guess that one of the two calls to node_save() can easily run into a problem.

The correct way in a scenario where you want to alter node properties (e.g. status, promote, title, ...) prior to inserting, is to use hook_node_presave(). If you want to update field values inside a hook_node_insert(), that should be done by calling field_attach_update('node', $node).

Using the save() method of entity_metadata_wrapper doesn't exactly feel good either. Looking at the code in EntityDrupalWrapper::save, which I suppose is the wrapper class that is responsible, it looks like node_save() is going to be called in the end too. But I have never really used Entity Wrapper, so I'm a bit short here.

Edit: Regarding entity_metadata:_wrapper, looking again at the code of entity_save() I realize that it's not node_save() that is called in the end, but that this is entirely handled by the Entity module. At the end it will end up here if I'm not mistaken: EntityAPIController::save. I'm not sure though how that explains the behavior described in the comment.

Answer 3

The reason why node_save($node->nid) gives you an error is because node_save takes node object to be saved, not a node id. Just change it to node_save($node) and it will work just fine.

In simple terms, node save is just a specific kind of entity save and just makes your life easier by doing things that you would have to do yourself (like in your case, node_save is one line, saving the entity does the same thing but you have to deal with metadata wrapper unnecessarily).