How to get just the term_ids from get_the_terms in WordPress

I am building a wordpress website that uses a custom AJAX filter that is linked to my Custom categories.

This is my function ajax-filter.php:

function filter() {
               $results = array();
            
            
           if (!empty($the_query->posts))
           {
               foreach ($the_query->posts as $post)
               {
                   $id = $post->ID;
                   array_push($results, array(
                       'id' => $id,
                       'tax' => get_the_terms( $post->ID, 'type', $id ),
        
                   ));
               }
           }
              wp_reset_postdata();
    
      $someJSON = json_encode($results);
      // Convert JSON string to Object
      $someObject = json_decode($someJSON);

      foreach($someObject as $key => $value) {
             echo $value->title;
        
            }
  die;
}
  add_action( 'wp_ajax_filter', 'filter' );
  add_action( 'wp_ajax_nopriv_filter', 'filter' );

My question is:

How can i use my data from tax to term-id in the way that i use in my ajax-filter.php? to use my data ($value->title)

Array
(
    [0] => Array
          [title] => title
          [tax] => Array
                (
                    [0] => WP_Term Object
                        (
                            [term_id] => 54
)

                )

        )

Answer

Firstly, well done on creating a Minimal example of your code, it makes it easier for us to see the problem and how to help 🙂

Now to your question:

There are 2 issues before you even get to your actual question

1. get_the_terms only takes 2 parameters – you don’t need to pass ni the 3rd parameter $id. The id is passed in the 1st parameter already
2. get_the_terms returns an array because a post can have multiple terms associated with it. You will need to consider how to handle multiple terms.

Handle a single term per post

For now, I’m going to assume you are only going to have a single term associated with the post, or if there are more only return the first.

Update your code as follows – the explanation for what is doing is in the comments:

  if (!empty($the_query->posts)){
       foreach ($the_query->posts as $post){

           // add this before you push the the values to your $results array

           // get an array with the term_ids only
           $term_ids = array();
           $term_objs = get_the_terms( $post->ID, 'type' );

           // get_the_terms returns an array of WP_Term objects
           foreach ($term_objs as $term_obj)
               $term_ids[] = $term_obj->term_id; // get the id from the WP_Term object

           // $term_ids could have many ids, so for the purpose of your example
           // we're just going to get the first one
           // You will need to decide how you'll handle multiple ids
           if ($term_ids) $term_id = $term_ids[0]; 

           $id = $post->ID;
           array_push($results, array(
               'id' => $id,
               [...] // your other values here
               'tax' => $term_id, // add just the single term id value
           ));
       }
   }

This will all it to your $results array as follows: Array ( [0] => Array ( [title] => title [tax] => 54 ) )

Now you can access the term id in your loop like this $value->tax, e.g.

foreach($someObject as $key => $value) {
     echo $value->title;
     echo $value->tax; // or whatever you want to do with it....
}

Handle Multiple terms per post

If you wanted to handle multiple terms, you could push the $term_ids array:

           foreach ($term_objs as $term_obj)
               $term_ids[] = $term_obj->term_id; 

           array_push($results, array(
               'id' => $id,
               [...] // your other values here
               'tax' => $term_ids, // add the array of  term ids
           ));

… and then loop through the array when you retrieve them:

foreach($someObject as $key => $value) {
    $term_ids = $value->tax;
    foreach ($term_ids as $term_id) 
        echo $term_id; // or whatever you want to do with it....
}