Query to get term id using post id?

Question

I know there is connection between post table with term table but I am unable to figure it out.

wp_terms, wp_termmeta, wp_term_relationships & wp_term_taxonomy relation is a little confusing. So, I am unable to write a query to get term id from post id.

Actual Problem:

I am using this piece of code to get an object and extract term id from that. But for some reasons, it is not working so I want to manually query in database to pull the term id and do rest of process.

get_metadata_by_mid('post', $id);

it returns this object: (on local machine)

stdClass Object
(
    [meta_id] => 1268   //this id is passed to function like get_metadata_by_mid('post', 1268);
    [post_id] => 222    //want to obtain this ID
    [meta_key] => _menu_item_url
    [meta_value] => 
)

Returns no result (on server) [so looking for alternative way]

NOTE:

• get_metadata_by_mid works on local machine but doesn't work on live (i don't know, why whereas I have same version in both environment)
• If someone can provide alternative way then it would be better than manual query.

Answer 1

It is not good practice to use query when you have already builtin functions but for your need.

Try this solution:

global $wpdb;
$meta = $wpdb->get_row( "SELECT * FROM `wp_postmeta`  WHERE `meta_id` = $id" );

//will return same object like returned by get_metadata_by_mid() function
print_r($meta);

Debugging Technique:

As you mentioned, get_metadata_by_mid() isn't working on live server. I would say,

1. Select any post id (for testing)
2. Login to phpmyadmin

3. Run this search query

   SELECT *  FROM `wp_postmeta` WHERE `meta_id` = ID_GOES_HERE
   //copy post_id from the results
   

4. Run this query

   SELECT *  FROM `wp_terms` WHERE `term_id` = POST_ID_GOES_HERE
   

Try to match the process on both (local & live) server. Hopefully, it will help you identify problem.

Answer 2

I'm not sure what you are trying to accomplish.

It seems you are trying to get the terms associated to a post, but the function get_metadata_by_mid gets Metadata.

If you are indeed trying to get all terms associated to a specific post, you can use the function wp_get_object_terms or wp_get_post_terms.

If you are trying to do something else, please restate your question to better explain what the intended result is ;)

Answer 3

the relationship of post and term you want is in table wp_term_relasionship. The object id equal with post_id So you can write your own query to access that