Wordpress Taxonomy - how does it know which object_id?

Question

I'm working on a project and would like to create a similar functionality that Wordpress has for taxonomy.

I'm not quite sure how it all works though.

They have 3 tables that are related:

wp_terms (
   term_id,
   name,
   slug,
   term_group
)

wp_term_taxonomy(
   term_taxonomy_id,
   term_id,
   taxonomy,
   description,
   parent,
   count
)


wp_term_relationships(
   object_id,
   term_taxonomy_id,
   term_order
)

From what I can tell, object_id is a generic name for what is either a link_id or post_id, but how do you know which one it is to query against it?

It also seems like wp_terms could be combined with wp_term_taxonomy. wp_term_taxonomy has the 'taxonomy' column, which is 'category' or 'link_category' by default, but other than that it just seems to reference the term_id, which has the slug and name.

Any clarity would be awesome... really not seeing how this fits together. Thank you!

Answer 1

1. assume that wp_terms is a master table of category.

2. wp_term_taxonomy is a table in which you can define categories hierarchy. Below are description of fields

   term_taxonomy_id = primary key(i think it is same as term_id most of the time)

   term_id = reference key to term_id of wp_terms table.

   taxonomy = type of category(category=post category, link_category= link category,post_tag = tags associated with posts, nav_menu = navigation menu, etc. )

   parent = id of parent category

3. assume that wp_term_relationships is a relationship table of product and category. where object_id is product id and term_taxonomy_id is category id