Sort by ACF field in the products in my Custom Post Type in Wordpress

Question

Could you please tell me how to sort my products(it is my custom post type) by the field(see picture) in ACF ?

Here is my custom field code:

    /*******            *******/
/*   CUSTOM POST TYPE     */
/*******            *******/

// Custom Post Type - product
function register_post_product() {
  $labels = array(
    'name'               => __( 'Products', '_tk' ),
    'singular_name'      => __( 'Product', '_tk' ),
    'add_new'            => __( 'Add product', '_tk' ),
    'add_new_item'       => __( 'Add New product', '_tk' ),
    'edit_item'          => __( 'Edit product', '_tk' ),
    'new_item'           => __( 'New product', '_tk' ),
    'all_items'          => __( 'All products', '_tk' ),
    'view_item'          => __( 'View product', '_tk' ),
    'search_items'       => __( 'Search product', '_tk' ),
    'not_found'          => __( 'No product found', '_tk' ),
    'not_found_in_trash' => __( 'No product found in the Trash', '_tk' ), 
    'parent_item_colon'  => '',
    'menu_name'          => __( 'Products', '_tk' ),
  );
  $args = array(
    'labels'            => $labels,
    'hierarchical'      => true,
    'supports'          => array( 'title', 'editor', 'page-attributes', 'thumbnail' ),
    'public'            => true,
    'show_ui'           => true,
    'show_in_menu'      => true,
    'show_in_nav_menus' => true,
    'publicly_queryable' => true,
    'exclude_from_search' => false,
    'has_archive'       => true,
    'rewrite'           => array('slug' => 'produkty','with_front' => false),
    'menu_position'     => 6,
    'menu_icon'         => 'dashicons-hammer'
  );
  register_post_type( 'product', $args ); 
}
add_action( 'init', 'register_post_product' );

I made some search in google and I tried to sort it like that:

add_filter( 'pre_get_posts', 'my_get_posts' );
function my_get_posts( $query ) {
      $query->set( 'orderby', 'meta_value_num' );
      $query->set( 'order', 'ASC' );
      $query->set( 'meta_query','capacity');

      return $query;
}

But with no results.

Answer 1

try this below function for pre_get_posts in wordpress

<?php
add_filter( 'pre_get_posts', 'my_get_posts' );
function my_get_posts( $query ) {

  $query->set( 'post_type', 'product' );
  $query->set( 'meta_key', 'capacity' );
  $query->set( 'orderby', 'meta_value' ); // meta_value_num or meta_value
  $query->set( 'order', 'ASC' );


  return $query;
}
?>

Answer 2

Most likely the problem is $query->set( 'meta_query','capacity');

meta_query should be an an array, like

array( array('key' => 'capacity', 
             'value' => array(0, 1000), 
             'compare' => 'BETWEEN',
             'type' => 'numeric', 
     ));

https://codex.wordpress.org/Class_Reference/WP_Query