Overview
Wondering how the Meta Box plugin stores custom field value in the database? Understanding this can help you get the custom field value easily and understand the returned value from get_post_meta or helper functions.
For all custom fields, the id is always the meta_key and the value is the meta_value in the wp_postmeta table. The sections below describe how the value is formatted.
Non-cloneable fields
For non-cloneable fields, the plugin stores field value in the data base in a WordPress-compatible way as following:
- If field has single value, it will be saved in single row in the post meta table.
- If field has multiple values (set by
'multiple' => truelikeselect,checkbox_list,file,image, etc.), each value will be saved in single row in the post meta table.
This way you can use add_post_meta or update_post_meta to update meta values and get_post_meta to retrieve them.
Cloneable fields
For cloneable fields, cloned values are stored as a serialized array in a single row in the post meta table.
The plugin does not store cloned values in separated rows in the database because it’s confusing that we don’t know these are values of clones, or values of the field with 'multiple' => true. To make it work for all field types and for consistency, storing cloned values in a single row of the database is a better choice.
Due to this reason, you still can use get_post_meta function to retrieve field value from the database (WordPress automatically unserializes string and returns an array). You will get an array of all cloned values.
Summary:
| Cloneable | Multiple | Custom Field Value |
|---|---|---|
| N | N | Single row |
| N | Y | Multiple rows |
| Y | N | Serialized array [value1, value2] in a single row |
| Y | Y | Serialized of 2-dimensional array [[value11,value12], [value21, value22]] in a single row |
Since version 4.14.7, you are able to store cloned values in multiple rows in the database. See this post for more details.
Field value
For normal fields, the saved value in the database is the value entered or selected by users. But for some specific fields, the stored values is not as obvious as that (for example, checkbox saves the checked/unchecked status as 1 and 0). Please see more details in each field in the left menu, section Fields.
Notes
Although you can use get_post_meta to retrieve meta value, it’s recommended to use helper functions to get the value and display it in the frontend. The helper function takes care of all the logic above and returns to you the needed data in a correct format.
To understand how the value is stored in the database, please use print_r function, like this:
$value = get_post_meta( get_the_ID(), 'field_id', true ); // Last param should be 'false' if field is multiple
echo '<pre>';
print_r( $value );
echo '</pre>';