Get post categories

Question

I want te make a filter based on post-categories. I'm trying to add the category-names in a data-category-attribute, but It doesn't seem to work. This is what I tried:

<article id="post-<?php the_ID(); ?>" <?php post_class(); ?> data-category="<?php $category_detail=get_the_category(); foreach($category_detail as $cd){ $cd->cat_name;}?>">
    <header class="entry-header">
        <?php
        if ( is_singular() ) {
            the_title( '<h1 class="entry-title">', '</h1>' );
        }
        else {
            the_title( '<h2 class="entry-title"><a href="' . esc_url( get_permalink() ) . '" rel="bookmark">', '</a></h2>' );
        }

        if ( 'post' === get_post_type() ) {
            ?>
            <div class="entry-meta">
                <?php dfib_theme_entry_meta(); ?>
            </div>
        <?php } ?>
    </header>
    <?php dfib_theme_post_thumbnail(); ?>
        <div class="entry-content">             
            <?php 
                the_excerpt();

            wp_link_pages( array(
                'before' => '<div class="page-links">' . esc_html__( 'Pages:', 'dfib-theme' ),
                'after'  => '</div>',
            ) );
            ?>
        </div>
    <footer class="entry-footer">
        <a href="<?php the_permalink(); ?>" class="btn">Meer info</a>
    </footer>
</article>

What am I doing wrong here?

Answer 1

You'll need to echo back your results in PHP.

foreach($category_detail as $cd){ echo $cd->cat_name; }

Also you might want to consider putting something between each category. If you have categories/terms like Blue, Red, Green. Then how you are currently looping over them, it will print it back as:

data-category="BlueRedGreen"

Hope that helps!!