Adding meta data to an attachment post

I want to add a meta data to my attachment posts, so I can get them in order by meta value later. That meta value would be 'price'.

So I thought this could work:

I have this args:

$args = array(
'order'          => 'ASC',
'post_type'      => 'attachment',
'post_parent'    => $post->ID,
'post_mime_type' => 'image',
'post_status'    => null,
'numberposts'    => -1,
);

Then I get posts (attachment posts) with $att_posts = get_posts($args);

Then I would like to add to each attachment post, a meta data called 'price', which value I get by get_post_meta($post->ID, 'key', true)['price'];.

So I thought this would do the work to add the meta data:

foreach( $att_posts as $att ){

  wp_update_attachment_metadata(
    $att->ID, 
    array( "price" => get_post_meta( $post->ID, 'key', true )['price'] ) )
  );

}

So i declared other args again but this time to order by 'meta_value_num', with meta key 'price'.

But it didn’t work.

Any body knows a simple way to make that possible? Any tips?

Thanks.

EDIT:

Here is all my code to get attachment images ordered by 'meta_key' 'price'.

$args = array(
  'order'          => 'ASC',
  'post_type'      => 'attachment',
  'post_parent'    => $post->ID,
  'post_mime_type' => 'image',
  'post_status'    => null,
  'numberposts'    => -1,
);


$att_posts = get_posts($args);

if ($att_posts) {
  foreach( $att_posts as $att ) {
    wp_update_attachment_metadata(
      $att->ID,
      array( 'price' => get_post_meta( $post->ID, 'price', true ) )
    );
  }
}


$args = array(
  'order'          => 'ASC',
  'orderby'        => 'meta_value_num',
  'meta_key'       => 'price',
  'post_type'      => 'attachment',
  'post_parent'    => $post->ID,
  'post_mime_type' => 'image',
  'post_status'    => null,
  'numberposts'    => -1,
);


$attachments = get_posts( $args );
if ( $attachments ) {
  foreach ( $attachments as $attachment ) {
    echo '<a href="https://wordpress.stackexchange.com/questions/181462/. $surl ."https://wordpress.stackexchange.com/" . $post->post_name. '>' .
    wp_get_attachment_image( $attachment->ID, 'thumbnail_large' ) . '</a>';
  }
} else {
  echo '<a href=".$surl."https://wordpress.stackexchange.com/" . $post->post_name . '>' .
  '<div class=\'thumbnail-small-img-search\'></div>' . '</a>';
}

But still doesn’t work.

Another way of asking is: How can I add meta data to attachment posts. And later, get the attachment posts ordered by this meta data called 'price'.

The objective of this is to display a paged list of posts with images ordered by price from cheapest to expensive.

This would be invoked by a submit button to one page of the website.

So since attachments are post types, you should be able to assign them postmeta like any other post type.

Using the update_post_meta function should get you where you need to be.

update_post_meta( $attachment_id, 'price', $price );

http://codex.wordpress.org/Function_Reference/update_post_meta

Then run your query based on a meta key.

$args = array(
'order'          => 'ASC',

'post_type'      => 'attachment',
'post_parent'    => $post->ID,
'post_mime_type' => 'image',
'post_status'    => null,
'numberposts'    => -1,

'meta_key'       => 'price',
);

http://codex.wordpress.org/Template_Tags/get_posts#Parameters