How to save multiple values with same meta_key, each value linked to another tag id

Question

Let´s say a user signs up to multiple memberships, each on a different date.

User signs up to:

• Membership A on 05.03.2021
• Membership B on 17.05.2021
• Membership C on 29.07.2021

I would like the dates for that user to be saved with the same meta_key. Each saved value/date should be linked to the specific membership, so that I can run a check and get the date when the user signed up for a specific membership.

I have the following so far:

$parameters = array(
    'member_id' => $user_id,
    'membership' => array (
        array (
        'tags'      =>  $tags,
        'datetime'  =>  time(),     
        )
        )
);

 add_user_meta( $user_id, 'membership', $parameters );

I would want to have the result for a user be something like:

membership:

[0]
    Tag: Membership A
    Date: 05.03.2021
[1]
    Tag: Membership B
    Date: 17.05.2021
[2]
    Tag: Membership C
    Date: 29.07.2021

In the var_dump it would look something like, where the number of sub-arrays for "membership" will be different per user, depending on the number of memberships they have assigned to them.

array(2) {
  ["member_id"]=>
  string(2) "12"
  ["memberships"]=>
  array(3) {
    [0]=>
    array(2) {
      ["membership"]=>
      string(5) "membership A"
      ["datetime"]=>
      int(1616239233)
    }
    [1]=>
    array(2) {
      ["membership"]=>
      string(5) "membership B "
      ["datetime"]=>
      int(1616239233)
    }
    [2]=>
    array(2) {
      ["membership"]=>
      string(5) "membership C"
      ["datetime"]=>
      int(1616239233)
    }
  }
}

I´m sure I am missing something, look forward to hearing your thoughts. Thanks

Answer 1

You can use insert_user_meta($user_id,'meta_key','meta_value');

when you want to get that keys, you can get like $keys = get_user_meta($user_id,'meta_key');

in $keys variable you get an array of all keys.

Answer 2

You've made some fatal misunderstandings that are not supported by the documentation.

1. Meta keys are not unique
2. If you store something then retrieve it you will get what you originally stored
3. It's a good idea to store arrays and objects in meta

Meta keys are not unique

You can have multiple post meta with the same name. When you call add_user_meta you are not updating data, you are adding additional data. Now there are 2 membership post metas. Call it again and there will be 3.

add_user_meta( $user_id, 'example', 'test' );
add_user_meta( $user_id, 'example', 'test' );
add_user_meta( $user_id, 'example', 'test' );

$examples = get_user_meta( $user_id, 'example', false );
foreach ( $examples as $example ) {
    // there are 3 examples
}

If you store something then retrieve it you will get what you originally stored

Why would it return just the memberships sub-array? If you store something, you get it back when you retrieve it, not a sub-part of it.

Use get_user_meta to retrieve what you stored.

It's a good idea to store arrays and objects in meta

What if I want all users with a particular membership ID? It can't be done! You can't query inside that value. You can't query inside serialised objects/arrays.

Your membership_id should be... a user meta named membership_id, and each individual membership should be a separate meta.