Wordpress ACF plugin - how to order by date field - wordpress

Question

I am using Advanced custom Fields plugin to create an event date in a custom post. I would like to order my events by that date, but it doesn't works for me:
<div class="column one">
<?php
$args = array(
'post_type' => 'formation',
'posts_per_page' => -1,
'post_status' => 'publish',
'meta_key' => 'date_formation',
'orderby' => 'meta_value_num',
'order' => 'DESC'
);
$posts_query = new WP_Query( $args );
while ($posts_query->have_posts()) : $posts_query->the_post();
$presentation = get_field('date_formation');
$date_formation = mysql2date( 'j F Y ', $presentation);
$lieu = get_field('adresse_formation');
?>
<div class="column one-third eventpost">
<div class="event-col">
<?php echo '<h4>'.$date_formation.''.$lieu.'</h4>'; ?>
<?php if( !is_single() ) {?><?php the_excerpt(); ?> <?php }else{ ?>
<?php the_content(); ?>
<?php } ?>
<p>En savoir plus<i class="icon-right-open"></i></p>
</div>
</div>
<?php endwhile; wp_reset_query(); ?>
</div>

Answer 1

Try to use Parham's solution from this question. You'll need to modify it a bit like so:
<div class="column one">
<?php
function wpse_130954_orderby_fix($pieces){
global $wpdb;
$pieces['where'] .= " AND $wpdb->postmeta.meta_key = 'date_formation'";
$pieces['orderby'] = "$wpdb->postmeta.meta_value DESC";
return $pieces;
}
add_filter( 'posts_clauses', 'wpse_130954_orderby_fix', 20, 1 );
$args = array(
'post_type' => 'formation',
'posts_per_page'=> -1,
'post_status' => 'publish',
);
$posts_query = new WP_Query( $args );
while ($posts_query->have_posts()) : $posts_query->the_post();
$presentation = get_field('date_formation');
$date_formation = mysql2date( 'j F Y ', $presentation);
$lieu = get_field('adresse_formation');
?>
<div class="column one-third eventpost">
<div class="event-col">
<?php echo '<h4>'.$date_formation.''.$lieu.'</h4>'; ?>
<?php if( !is_single() ) {?><?php the_excerpt(); ?><?php }else{ ?><?php the_content(); ?><?php } ?>
<p>En savoir plus<i class="icon-right-open"></i></p>
</div>
</div>
<?php endwhile; wp_reset_query(); ?>
<?php remove_filter( 'posts_clauses', 'wpse_130954_orderby_fix', 20 ); ?>
</div>