According to the announcement on the Make WordPress Core blog post it appears that to use post meta on a post things have changed quite a bit.

I'm trying to get a simple block to read and save data from a custom field, and for some reason each time I hit save the data is lost.

I start by registering the custom field in PHP (attached to the init hook):

  register_post_meta('ebook', 'main_video', array(
    'show_in_rest' => true,
    'single' => true,
    'type' => 'string',

and from the block controls I'm trying to then read and set methods to write into that field as follows:

const postType = useSelect((select) => select('core/editor').getCurrentPostType(), []);
  const [meta, setMeta] = useEntityProp('postType', postType, 'meta');
  const url = meta && meta['main_video'];
  const updateUrl = (newValue) => {
    setMeta({ ...meta, main_video: newValue.url });

Both url and updateUrl variables are then consumed by a gutenberg component:

   value={{ url }} 

If I log the values I can see data coming in and being updated, but as soon as I hit save on the post everything is reset.

The ebook post type where this custom field is being registered has support declared for custom-fields.

I've followed the official docs on this a few times and couldn't get it to work as they describe.

Am I missing a key step here or something's amiss?

  • Did you find solution to the problem ?
    – andrew
    May 11 at 0:52
  • At a glance, this all looks alright to me. Have you continued to experience this issue?
    – bosco
    Jun 11 at 20:20

I think your onChange function needs to pass the value, like onChange={(value) => updateUrl(value)}


I am very late at this, but I think the problem here was that at registration code for your custom post type ebook (which you did not show) you were missing supports for custom-fields in args array:

'supports'              => [ 'title', 'editor', 'custom-fields' ]

and also

'show_in_rest'          => true

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