Dependency between “custom post type” and “custom fields” in WordPress

In WordPress, a custom post type and custom fields are related in the sense that custom fields are used to store additional information about the custom post type.

Here’s an example of how the dependency works:

1. You create a custom post type called “book” using the register_post_type function.
2. You create custom fields for the “book” custom post type using the add_meta_box function and the update_post_meta function.
3. When you create a new “book” post, you can fill in the custom fields with information specific to that book, such as the author, publisher and year.
4. When you save the “book” post, the custom field values are also saved in the WordPress database and can be retrieved later using the get_post_meta function.
5. You can also display these custom fields in the front-end and use them in your theme’s templates by fetching these values with get_post_meta function

In this way, custom fields provide a way to add additional information to custom post types in a structured way, and the custom post type provides a way to organize and display this additional information in the WordPress admin and front-end.