Cloning fields

The clone feature of Meta Box allows you to create multiple inputs from a text, textarea, select, ... fields without declaring many fields in the code. Combining the clone feature with groups gives you a flexible way to define repeatable content.

Clone is a feature

The difference between Meta Box and other plugins is that the clone feature can be applied to all field types. And it's a feature, not a field type. Then, every field or group can be cloneable or repeater. They are called cloneable fields or cloneable groups.

Making a field cloneable

When editing a field, turn on this Cloneable option in the settings of the field:

After turning in the Cloneable option, other clone settings will appear.

Not a premium user?

You can see the settings visually as above since this instruction uses Meta Box Builder extension, which is a premium extension providing the UI to create fields, and is already bundled in Meta Box AIO and MB Core. If you're not a premium user, please purchase a license to use it. However, you can do this with code.

No matter what you are using the UI or code, this is a brief description of the clone settings. The keys are for reference in code.

Settings	Key	Description
Cloneable	clone	Make the field cloneable? true or false (default). Optional.
Sortable	sort_clone	Allow to drag-and-drop sort clones. true or false (default).
Clone default value	clone_default	Clone the default value of the field? true or false (default).
Clone as multiple	clone_as_multiple	Whether to store cloned values in multiple rows in the database
Max number of clones	max_clone	Limit the number of clones. Must be greater than 2. Optional.
Min number of clones	min_clone	Minimum number of clones. Optional.
Add more text	add_button	The text for Add more clone button. Optional. Default "+ Add more".
Clone empty start	clone_empty_start	Allows no fields except the Add more button to show up. true or false (default). Optional.

After saving the field group, in the post editor, you'll see an + Add more button below the field input. Clicking it allows you to enter more values:

If you're a developer and want to use code, then you need to add the clone settings into the field settings:

add_filter( 'rwmb_meta_boxes', function ( $meta_boxes ) {
    $meta_boxes[] = [
        'title'      => 'Event details',
        'post_types' => 'event',
        'fields'     => [
            [
                'name'  => 'Date and time',
                'id'    => 'datetime',
                'type'  => 'datetime',
                'clone' => true,
                // Other clone settings
            ],
            [
                'name' => 'Location',
                'id'   => 'location',
                'type' => 'text',
            ],
            [
                'name'          => 'Map',
                'id'            => 'map',
                'type'          => 'osm',
                'address_field' => 'location',
            ],
        ],
    ];

    return $meta_boxes;
} );

Data of cloneable fields

For cloneable fields, values are stored as a serialized array in a single row in the database, unless you set 'clone_as_multiple' => true.

Using serialized data has some benefits:

• Works for all field types, including nested groups.
• Works perfectly with the helper function or with WordPress's get_post_meta function (WordPress automatically deserializes string and returns an array).
• Reduces the database size (number of rows), especially when you have nested groups of many fields.

Query posts by cloneable fields

By default, cloned values are stored as a serialized array, which doesn't allow you to query posts by these values. For example, if you have a cloneable field start_date for the event post type, and you want to query events in May 2019 like this:

$args = [
    'post_type'  => 'event',
    'meta_query' => [
        [
            'key'     => 'start_date', // This field is cloneable
            'value'   => ['2019-05-01', '2019-05-31']
            'compare' => 'BETWEEN',
        ],
    ],
];
$query = new WP_Query( $args );

Then it doesn't work.

To solve this problem, you need to enable the Clone as multiple settings for the field.

With that, Meta Box will save cloneable values in multiple rows in the database, where each row contains one value. That means if start_date has 2 values ['2019-05-01', '2019-04-30'], it will be saved in 2 rows in the database, one for 2019-05-01 and one for 2019-04-30. The data is not serialized anymore. And thus, your above query will work!

Default values

When making a field to be cloneable, its data is an array of cloned values. So, the std parameter (default value) should represent this structure, e.g. array of cloned values.

add_filter( 'rwmb_meta_boxes', function ( $meta_boxes ) {
    $meta_boxes[] = [
        'title'      => 'Event details',
        'post_types' => 'event',
        'fields'     => [
            [
                'name'  => 'Date and time',
                'id'    => 'datetime',
                'type'  => 'datetime',
                'clone' => true,
                'std' => [
                    '2022-04-20',
                    '2022-04-21',
                ],
            ],
            [
                'name' => 'Location',
                'id'   => 'location',
                'type' => 'text',
            ],
            [
                'name'          => 'Map',
                'id'            => 'map',
                'type'          => 'osm',
                'address_field' => 'location',
            ],
        ],
    ];

    return $meta_boxes;
} );