Get taxonomy terms only of the WP_Query current posts

Question

I'm trying to find a way to not show all the terms of a taxonomy, but only the terms of the current displayed posts of the wp_query.

The code below displays all terms for 'brands' taxonomy and the query displays all products of the current category, i want to display only the terms that are set on the products that are displaying.

$marcas_terms = get_terms([
  'taxonomy' => 'brands'
]);

foreach ($brands_terms as $brand_term) { 
  <input type="checkbox" id="<?php echo $brand_term->term_id; ?>" name="marca" value="<?php echo $brand_term->term_id; ?>">
  <label for="<?php echo $brand_term->term_id; ?>"><?php echo $brand_term->name; ?></label>
}

$args = array(
  'post_type' => 'product',
  'product_cat' => get_queried_object()
);

$query = new WP_Query( $args );
   if ( $query->have_posts() ) {
     while( $query->have_posts() ) : $query->the_post();

        get_template_part("templates/product-content-category");

     endwhile;
   } wp_reset_postdata(); 

Answer 1

You'd probably do something like this

$args = array(
  'post_type' => 'product',
  'product_cat' => get_queried_object()
);
$query = new WP_Query( $args );

$termsInPosts = array();
if ( $query->have_posts() ) {
    while( $query->have_posts() ) : $query->the_post();
        $postTerms = wp_get_post_terms(get_the_ID(), 'brands', array('fields' => 'term_id'));
        foreach ($postTerms as $postTerm)
            if (!in_array($postTerm->term_id, $termsInPosts))
                $termsInPosts[] = $postTerm->term_id;
    endwhile;
} 

$marcas_terms = get_terms([
  'taxonomy' => 'brands',
  'include' => $termsInPosts
]);

foreach ($brands_terms as $brand_term) { 
  <input type="checkbox" id="<?php echo $brand_term->term_id; ?>" name="marca" value="<?php echo $brand_term->term_id; ?>">
  <label for="<?php echo $brand_term->term_id; ?>"><?php echo $brand_term->name; ?></label>
}

if ( $query->have_posts() ) {
    while( $query->have_posts() ) : $query->the_post();
        get_template_part("templates/product-content-category");
    endwhile;
} 

wp_reset_postdata(); 

What you're doing is just running through the loop before hand, getting the id's of terms within the posts, adding to an array, then when you call get_terms() you're using include to include only the terms you found.

I haven't tested this code, it's freehand, but it should work, or at least steer you in the right direction.

Hope that helps.

Answer 2

I think we can simplify it with the object_ids argument of get_terms(), with post IDs plucked from the given posts array.

Here's an untested skeleton, if I understand the problem correctly:

// Your post query
$query = new WP_Query( $args );

if( $query->have_posts() ) {

    // Get terms from the post IDs of the above post query
    $brand_terms = get_terms( [
        'taxonomy'   => 'brands',
        'object_ids' => wp_list_pluck( $query->posts, 'ID' ),
    ] );

    // Your terms loop
    foreach ( $brands_terms as $brand_term ) { 
        // ...
    }

    // Your posts loop
    while( $query->have_posts() ) { 
        $query->the_post();
        get_template_part( "templates/product-content-category" );
    }

    wp_reset_postdata(); 
}

Hope it helps.