Updating meta value for specific ids

I am updating post meta with this

update_post_meta( '3100', 'mymetakey', 'mymetavalue' );

How can I add this metakey and metavalue not only to post ID 3100, but several other IDs?

Answer

You can define array of post ids and then you can iterate loop of ids. Try the below code.

$postIds = array( 3100, 1234, 5678....);

foreach ( $postIds as $key => $post_id ) {
    update_post_meta( $post_id, 'mymetakey', 'mymetavalue' );
}

Update as per OP comment.

$args = array(
    'post_type'      => 'product',
    'posts_per_page' => -1,
    'tax_query'      => array(
        array(
            'taxonomy' => 'product_cat', // custom taxonomy
            'field'    => 'slug',
            'terms'    => 'your-category-slug', // taxonomy term (category)
        )
    )
);

$products = new WP_Query( $args );

if( $products->have_have() ){ while ( $products->have_have() ) { $products->the_post();
    
    update_post_meta( get_the_ID(), 'mymetakey', 'mymetavalue' );
    
} wp_reset_postdata(); }