Understanding ACF data storage

• iamrobertandrews

• December 9, 2022 at 7:07 am

I know you have dealt with a lot of “How does ACF store data?” questions over the years.

I have been noting-down what I think I have learned, and I want to post it for sense-checking…

### Field Group – wp_posts (acf-field-group)

Field Groups (for posts) are stored in the wp_posts as post_type acf-field-group.

Eg.
– post_title – Post – Article, Viewpoint & Report fields
– post_name – post-article-viewpoint-report-fields
– post_excerpt – source_url
– post_content –
`json
a:13:{s:8:”location”;a:3:{i:0;a:1:{i:0;a:3:{s:5:”param”;s:9:”post_type”;s:8:”operator”;s:2:”==”;s:5:”value”;s:7:”article”;}}i:1;a:1:{i:0;a:3:{s:5:”param”;s:9:”post_type”;s:8:”operator”;s:2:”==”;s:5:”value”;s:9:”viewpoint”;}}i:2;a:1:{i:0;a:3:{s:5:”param”;s:9:”post_type”;s:8:”operator”;s:2:”==”;s:5:”value”;s:6:”report”;}}}s:8:”position”;s:15:”acf_after_title”;s:5:”style”;s:7:”default”;s:15:”label_placement”;s:3:”top”;s:21:”instruction_placement”;s:5:”label”;s:14:”hide_on_screen”;s:0:””;s:11:”description”;s:0:””;s:12:”show_in_rest”;i:0;s:18:”acfe_display_title”;s:0:””;s:13:”acfe_autosync”;s:0:””;s:9:”acfe_form”;i:0;s:9:”acfe_meta”;s:0:””;s:9:”acfe_note”;s:0:””;}
`

### Post Field – wp_posts (acf-field)

Individual fields (items of a Field Group) (for posts) are stored in the wp_posts as post_type acf-field.

Eg.
– post_title – Source URL
– post_name – field_5b39e6dc170b7
– post_excerpt – source_url
– post_content –
`json
a:7:{s:4:”type”;s:3:”url”;s:12:”instructions”;s:0:””;s:8:”required”;i:0;s:17:”conditional_logic”;i:0;s:7:”wrapper”;a:3:{s:5:”width”;s:0:””;s:5:”class”;s:0:””;s:2:”id”;s:0:””;}s:13:”default_value”;s:0:””;s:11:”placeholder”;s:0:””;}
`

—

## Post meta data

### wp_postmeta

The wp_postmeta table stores meta fields for WordPress posts.
Each meta item has an entry, linked to the post ID.
– meta_id
– post_id
– meta_key
– meta_value

#### 1. Actual data

ACF stores the **data** as WordPress expects, eg:
– meta_key: source_url
– meta_value: [https://www.example.com/my/added/page.html](https://www.example.com/my/added/page.html)

#### 2. ACF meta

However, it also keeps a second meta item to link it to the ACF Field Group information.
– meta_key: _source_url
– meta_value: field_5b39e6dc170b7

This is a signpost that allows ACF to link this field back to the Field data.
– “field_5b39e6dc170b7” is the ACF name of the native field “source_url”
– “field_5b39e6dc170b7” the post_name of the field stored in wp_posts, with post_title “Source URL”.

#### ACF saves postmeta with null values

Even for actual WordPress postmeta data, ACF appears to create wp_postmeta records for ACF fields with no meta_value. (2022-12-09: there were 24,013 such records with zero meta_value).

## Summary

– Field Group information is stored as posts.
– Field information is stored as posts.
– ACF keeps 2x as much postmeta as necessary (2022-12-09: 237,853 entries in wp_postmeta)
– It also keeps blank meta records.

—

## Questions

– Will deleting a field delete the corresponding wp_post item of type acf-field?
– Will deleting a field group delete the corresponding wp_post item of type acf-field-group?

– In a scenario in which ACF is no longer used, deleting all wp_postmeta with values field_* should help tidy things up, right?
– If I want to delete all the blank postmeta records that have been saved, I should select them with SELECT * FROMwpcxt_postmetaWHEREmeta_keyIS NOT NULL ANDmeta_value= '' and delete, right?

• John Huebner

• December 18, 2022 at 11:28 am

– Will deleting a field delete the corresponding wp_post item of type acf-field?

Yes

– Will deleting a field group delete the corresponding wp_post item of type acf-field-group?

Yes, an it will also delete all of the fields in that field group

– In a scenario in which ACF is no longer used, deleting all wp_postmeta with values field_* should help tidy things up, right?

This will only delete the field key references and not the field data

– If I want to delete all the blank postmeta records that have been saved, I should select them with SELECT * FROMwpcxt_postmetaWHEREmeta_keyIS NOT NULL ANDmeta_value= ” and delete, right?

Yes, this would delete all of the entries with empty values.

• iamrobertandrews

• March 30, 2023 at 8:37 am

@hube2 ,

Ages ago, you posted this code…

<?php 
  
  // this action is run by ACF whenever a field is deleted
  // and is called for every field in a field group when a field group is deleted
  add_action('acf/delete_field', 'delete_acf_content_on_delete_field');

  function delete_acf_content_on_delete_field($field) {
    // runs when acf deletes a field
    // find all occurences of the field key in all tables and delete them
    // and the custom field associated with them
    global $wpdb;
    // remove any tables from this array that you don't want to check
    $tables = array('options', 'postmeta', 'termmeta', 'usermeta', 'commentmeta');
    foreach ($tables as $table) {
      $key_field = 'meta_key';
      $value_field = 'meta_value';
      if ($table == 'options') {
        $key_field = 'option_name';
        $value_field = 'option_value';
      }
      $table = $wpdb->{$table};
      // this query gets all key fields matching the acf key reference field
      $query = 'SELECT DISTINCT('.$key_field.')
                FROM '.$table.'
                WHERE '.$value_field.' = "'.$field['key'].'"';
      $results = $wpdb->get_col($query);
      if (!count($results)) {
        // no content found in this table
        continue;
      }
      // loop through keys and construct list of meta_key/option_names to delete
      $keys = array();
      foreach ($results as $key) {
        $keys[] = $key; // delete acf field key reference
        $keys[] = substr($key, 1); // delete acf field value
      }
      // do escping of all values.... just in case
      $keys = $wpdb->_escape($keys);
      // delete all of the content
      $query = 'DELETE FROM '.$table.'
                WHERE '.$key_field.' IN ("'.implode('","', $keys).'")';
      $wpdb->query($query);
    } // end foreach table
  }

?>

For me, it doesn’t seem to fire when I delete a field (and re-save the group).

Any reason why, in 2023, that wouldn’t work?

Thanks.

• John Huebner

• March 30, 2023 at 9:20 am

No idea, but that is not a completely safe way to delete data. It would only be safe where there is a unique field name that is never repeated in any ACF field group.

Not sure where you got that, but I don’t even remember writing it. I can’t even be sure I tested it when I wrote it. There could have been some change in ACF since then. A quick look at the ACF code shows the hook should still be firing but I did not do a thorough search of the code.

I can tell you that I’ve written a lot of code here that I’ve never tested and this would likely fall into the category of things I’ve never used or tested because I don’t use unique field names and I don’t have not worried about stray data in the database for a long time.