Add hook for block deletion so post meta can be removed

[diegoliv]

Issue Overview

When you create a block that have a attribute set as meta, Gutenberg saves this same attribute as post meta, which is expected. However, if you remove the block and save the post, the post meta is still stored on the database.

Steps to Reproduce (for bugs)

1. Create a custom block, and set any random attribute as source: 'meta'.
2. Change the attribute value and save the post.
3. Check on the frontend, using get_post_meta, the value of the post meta from that specific block.
4. Now go back to the editor, remove the block and update the post.
5. Go back to the frontend, and check again the value of the post meta. It is still there.

Expected Behavior

When the block is deleted, the post meta should be deleted as well. Unless there is another block of the same type for the post. On this case, post meta should be treated on a block basis, not on a post basis (related to #5599)

Current Behavior

Post meta is stored when you add one block, changes when you change the attribute on any instance of the block for the respective post, but it is not removed from the database if you remove all block instances.

Related Issues and/or PRs

#5599

[ocean90]

See #4054 for previous discussion.

If the editor is not going to remove/reset them to default (see #6505) by default, there needs at least a hook on block delete that can be used to perform additional cleanups like deleting post meta.

[Luehrsen]

I would like to add importance to this issue. We are using blocks to control the existence of certain metadata (e.g. control template pieces outside of 'the_content()')

AFAIK there is currently no way to force the existance of a certain block, so the the problem is that we will have metadata existing without an interface to edit them. That is less than optimal.

[Luehrsen]

https://gist.github.com/Luehrsen/41d27f30eaca2d997a84898271c004c7

This is my current implementation. It works, but it has some issues. Sometimes the actions fire twice, sometimes I get a strange error from the rest API. (See screenshot)

But so far I am quite happy with the progress.

[danielbachhuber]

Re-titled issue as "Add hook for block deletion so post meta can be removed" to clarify its direction.

[aduth]

To me, ideally this is not something which occurs in the editor itself, as it's very possible someone may remove the block without interfacing with Gutenberg (by database, or wp_update_post). With server registration of blocks (#2751), it seems reasonable that in the updating of a post's content, we could detect whether a block is being removed which sources some attribute value from post meta, then delete the associated post meta from the server (admittedly only addresses wp_update_post, and not database manipulation, but a step in the right direction).

[hgezim]

Any updates on this?

[mitogh]

As a workaround of this I used componentWillUnMount and trigger an action there.

[gziolo]

Indeed, it makes a lot of sense what @aduth shared. Even if we would land #7325 proposed by @Luehrsen, this issue would still be present if someone uses REST API to remove one of the blocks. Given that mobile team is working on Gutenberg integration for the mobile app this issue will become even more prominent.

I'm wondering if the root issue shouldn't be moved to WordPress core now as the logic for saving blocks is there.

[youknowriad]

I'm going to close this now as a potential solution for this can't come from the block editor itself.
Please consider opening a trac ticket about this if needed.