This recipe uses one of the many parameters of the register_taxonomy function to remove the ability for book review creators and editors to create new book types and creates a drop-down list to be able to assign a single book type to reviews.

In this process, the recipe makes use of three functions related to storing and retrieving taxonomy entries related to posts. The first, wp_get_post_terms, retrieves an array of terms associated with a post based on its ID and the name of the taxonomy. The second, wp_set_post_terms, assigns a term to a post based on its ID and the taxonomy name. Finally, get_terms retrieves an array of all the terms in the taxonomy, ordered based on the query string found in the second argument.