I have a user base of hundreds of users, and trying to create a custom API endpoint to get users in a specific membership group.

The database structure is as follows (using Ultimate Member plugin):

  • User is stored in wpma_users table
  • User metadata in table wpma_usermeta contains user meta named mygroups, containing a value a:1:{i:0;s:3:"155";}
  • The 155 value is the ID of a term

I already tried this, with $groupid=155:

$args = array(
            'fields'    => 'all_with_meta',
            'tax_query' => array(
                  'taxonomy' => 'mygroups',
                  'field' => 'term_id',
                  'terms' => $groupid,
$user_query = new WP_User_Query($args);

When I var_dump get_terms(array('include' => $groupid)), an actual term is printed:

        ]=>string(8)"Example Group"[

Another way I tried, is using the meta_query instead of the tax_query:

'meta_query' => array(
                'key' => 'mygroups',
                'value' => $groupid,
                'compare' => 'LIKE',

This actually filters the query, but when I use $groupid=1, it filters where groupid contains 1, so also 10, 11, 100 etc.

Who can point me in the right direction to filter the user on mygroups the right way?

  • 2
    You need to ask this in an Ultimate Member plugin community, this isn't possible using generic WordPress
    – Tom J Nowell
    Commented Sep 23, 2022 at 12:24

2 Answers 2


This isn't possible, you can't safely/reliably query the internals of meta value strings that way, and you can't use it as a form of indirection:

  • You can query for substrings or for whole values, but you can't query the internals of serialised PHP values without major performance reliability and consistency issues
  • but if you could, or if it was just the plain number, there's no way to then take that and plug it into a term query
  • You can only use tax_query to find users in a given taxonomy, but your users don't have terms, and they aren't in a taxonomy.

User taxonomies are a thing, so be careful about what you're asking. Instead, you need to rephrase your question like this:

How do I find users with a specific value that's listed in the mygroups user meta field using WP_User_Query?

And the answer is, you can't. This is because mygroups is stored as a serialised PHP array, and you can't query sub-values of serialised values. E.g. you could use a LIKE style parameter to search for group 1 but it will also give you 10, 100, 41, etc It may even give you users who have a group number that is 1 digit long, and users that have 1 group even if that groups number is 9999.

It may be that there is a solution that uses features of the Ultimate Member plugin, but questions about that plugin and other 3rd party plugins are off-topic here and not in this stacks scope

  • Thanks for your extensive answer! Also, thanks for your clarification about taxonomies and terms. Since I could get specific terms with the Wordpress get_terms($id) method, I thought it would maybe be possible with native Wordpress filtering. I'll try the Ultimate Member form.
    – harmjanr
    Commented Sep 24, 2022 at 16:52

I found a solution, since the serialized array is always structured like this: ':"%s";', it is possible to write a meta_query like:

'meta_query' => array(
        'key' => 'mygroups',
        'value' => sprintf(':"%s";', $groupid),
        'compare' => 'LIKE'

Works like a charm!

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