How to explode single string IF it's used in shortcode

Question

I have a shortcode that works to display posts from specific categories, or a single post based on the post slug. I'm having trouble figuring out how to get it to display multiple posts based on their slugs though. I know I need to use explode, but I can't seem to get it right.

Here's the current working code:

add_shortcode( 'latest_post', 'latest_post_query_shortcode' );
function latest_post_query_shortcode(  $atts ) {
    ob_start();
    $atts = shortcode_atts( array(
            'posts_per_page' => '',
            'category' => '',
            'offset' => '',
            'post' => '',
    ), $atts );

    $args = array(
            'post_type'     => 'post',
            'post_status'   => 'publish',
            'posts_per_page'=> $atts['posts_per_page'],
            'offset'             => $atts['offset'],
        );
        
    // Add category if not empty
    if ( ! empty ( $atts['category'] ) ) {
        $args['tax_query']  = array( 
                array(
                    'taxonomy'  => 'category',
                    'field'     => 'slug',
                    'terms' => $atts['category'],
                ), 
            );      
    }
    
    // Add post if not empty
    if ( ! empty ( $atts['post'] ) ) {
        $args['name']  = $atts['post'];
    }
        $string = '';
        
    // The Query
    $query = new WP_Query( $args ); 

    // The Loop
    if ( $query->have_posts() ) { ?>
        <section class="recent-posts clear">
        <?php while ( $query->have_posts() ) : $query->the_post() ; ?>
            <article id="post-<?php the_ID(); ?>" <?php post_class( 'left' ); ?>>

                <?  echo '<a href="' . get_permalink( $_post->ID ) . '" title="' . esc_attr( $_post->post_title ) . '">';
                    echo get_the_post_thumbnail( $_post->ID, 'large' );
                    echo '</a>';
                    echo '<h2><a href="' . get_permalink( $_post->ID ) . '" title="' . esc_attr( $_post->post_title ) . '">';
                    echo get_the_title( $_post->ID);
                    echo '</a></h2>';

                ?>
            </article>
        <?php endwhile; 
        wp_reset_postdata();?>  
        </section>          
        <?php 
        $clean = ob_get_clean();
        return $clean;      
    }
}

I tried adding:

'name' => explode( ', ', $post),

inside

$args = array(

but that didn't return anything when I tried specifying two slugs, for example: [latest_post post="almond-cake, coconut-pie"] (If I use either one of those, it works, but not both.)

Additionally once I added the explode, it game me this warning everywhere else the shortcode was used:

Warning: trim() expects parameter 1 to be string, array given...

Answer 1

So from the WP_Query page, I found this, which is like $args['name'] but for when you want to search for many slugs:

post_name__in (array) – use post slugs. Specify posts to retrieve. (Will be available in version 4.4)

I think this is maybe what you need?

In that case you'd need to explode $atts['post'] on "," as you did, then pass that resulting array to post_name__in attribute in $attrs. You're getting that error resulting from trim because you're passing an array to the 'name' attribute in WP Query which is expecting a single slug name in a string.

I'd recommend you explode on "," first, without spaces, then strip off the white space from the resulting strings as that allows for much more freedom in how you (or other users) put stuff in the post attribute in the shortcode.

Let me know if that is or isn't on the right track or if you want more detailed code example

Answer 2

This works for me:

add_shortcode( 'latest_post', 'latest_post_query_shortcode' );
function latest_post_query_shortcode(  $atts ) {
        ob_start();
        $atts = shortcode_atts( array(
                        'posts_per_page' => '',
                        'category' => array(), // defined as array here
                        'offset' => '',
                        'post' => '',
        ), $atts );

        $args = array(
                'post_type'     => 'post',
                'post_status'   => 'publish',
                'posts_per_page'=> $atts['posts_per_page'],
                'offset'             => $atts['offset'],
        );

                
        // Add category if not empty
        if ( !empty( $atts['category'] ) ) {
            $terms = str_replace(' ', '', $atts['category']); // strip whitespace so admins don't have to remember whether or not to put a space after each comma
            $terms = explode(',', $atts['category']); // then get the array
            $args['tax_query']  = array( 
                    array(
                            'taxonomy'  => 'category',
                            'field'     => 'slug',
                            'terms' => $terms,
                    ), 
            );    
        }
        
        // Add post if not empty
        if ( ! empty ( $atts['post'] ) ) {
                $args['name']  = $atts['post'];
        }
                $string = '';
                
        // The Query
        $query = new WP_Query( $args ); 

        // The Loop
        if ( $query->have_posts() ) { ?>
                <section class="recent-posts clear">
                <?php while ( $query->have_posts() ) : $query->the_post() ; ?>
                        <article id="post-<?php the_ID(); ?>" <?php post_class( 'left' ); ?>>

                                <?  echo '<a href="' . get_permalink( $query->ID ) . '" title="' . esc_attr( $query->post_title ) . '">';
                                        echo get_the_post_thumbnail( $query->ID, 'large' );
                                        echo '</a>';
                                        echo '<h2><a href="' . get_permalink( $query->ID ) . '" title="' . esc_attr( $query->post_title ) . '">';
                                        echo get_the_title( $query->ID);
                                        echo '</a></h2>';

                                ?>
                        </article>
                <?php endwhile; 
                wp_reset_postdata();?>  
                </section>          
                <?php 
                $clean = ob_get_clean();
                return $clean;      
        }
}