Sending mails with wp_mail() to multiple recipients using wp_cron and dynamic email body data

Question

I have a frontend submission form, where users can add events to a custom post type. I want to send an email to each user 1 week before this event takes place.

The emails are sent via wp_cron. The function is called with a hook. It's working correctly, but I want to add custom values to the email body.

With my code its not possible to add dynamic value to the body template of my email.

With this function below, I loop through the events post type and get the required data

function leweb_get_events_detail() {

    // Query
    global $wp_query;

    // Arguments  
    $args = array(
        'post_type' => 'events',
    );

    // Start the Query
    $query = new WP_Query( $args );

    // The Loop
    if( $query->have_posts() ) {

        $results = array();

        while( $query->have_posts() ) {

            $query->the_post();             

            $event_date_timestamp = get_post_meta( get_the_ID(), 'event_date_timestamp', true );
            $future_timestamp = strtotime("+1 week");

            // Damit wird geprüft ob schon einmal diese Email gesendet wurde
            $notification = get_post_meta( get_the_ID(), 'event_creator_notification' );

            if( !in_array( '1week', $notification )  && $event_date_timestamp < $future_timestamp ) {

                $event_id = get_the_ID();
                $event_email = get_post_meta( get_the_ID(), 'event_email', true );

                $results[] = array( 
                                'event_id'      => $event_id, 
                                'event_date_timestamp' => $event_date_timestamp,
                                'event_email'     => $event_email,
                );

            }
        }

        return $results;

    }

    wp_reset_query();

}

The function below lets me fetch data from the post_meta array:

function leweb_get_values_from_post_meta( $meta = '') {

    $results = leweb_get_events_detail();

    $values = array();
    foreach( $results as $key => $value ){

        $values[] = $value[ $meta ];

    }

    return $values;
}

The function below is called from wp_cron. The email is sent to all recipients who match the above conditions and a value is added to the post meta, to prevent multiple sends of this email.

function leweb_send_mail_to_author() {


    // Alle Emails aus dem Array auslesen und für das BCC Feld im Email Header vorbereiten
    $emails = leweb_get_values_from_post_meta( 'event_email');

    if ( !empty( $emails ) ) {

        $emails = 'BCC: ' . implode( ',', $emails );

        // Email senden
        $to = '';
        $subject = 'Dein Event findet bald statt!';
        $body = file_get_contents( get_stylesheet_directory() . '/templates/email/event-creator-notification.php');
        $headers = array( 'Content-Type: text/html; charset=UTF-8','From: Example <[email protected]>', $emails );

        wp_mail( $to, $subject, $body, $headers );

        // Wert in post_meta eintragen um die Mehrfachsendung zu verhindern
        $post_id = leweb_get_values_from_post_meta( 'event_id');

        foreach( $post_id as $id ) {

            add_post_meta( $id, 'event_creator_notification', '1week' );

        }

    }

}

After I coded this I figured out. it's not possible to send dynamic content in the body of my email. The only way to achieve this, is to call the wp_mail() in foreach. But this would be heavy I think? It's possible that this job sends up to hundred emails per run in the future...

So I was wondering if there is another way to do this cleanly?

Answer 1

Here's your problem:

        $body = file_get_contents( get_stylesheet_directory() . '/templates/email/event-creator-notification.php');

file_get_contents literally just gets the contents of that file. There's no PHP execution. Instead, if you want to get the output of something as a variable, use output buffers, e.g.

ob_start(); // everything echo'd after this gets put in the buffer
get_template_part( 'templates/email/event-creator-notification' );
$body = ob_get_clean(); // get the buffers contents and stop output buffering