WP_Query about meta_key and its array value

Question

I am developing code with wordpress. Because of lacking abilities I am having some trouble.

construction of this questioning part in my wordpress

• custom-post-type : book // this is my custom-post-type.
• meta_key : date_all // this is my meta_key of 'book'.
• meta_value : array('year' => '2012', 'month =>'3', 'date' => '23', 'dw' => '2')

and thers are some book-posts (my custom post type). I am trying to query book-post which is corresponding conditions below:

• meta_key : date_all
• meta_value : year = 2018 & month = 3
• compare : >= or 'after'

I am making some code. but I don't know how to express the 'meta_value'. Because this is array value.

$args = array(
            'post_type' => 'book',
            'posts_per_page' => -1,
            'meta_key' => 'date_all',
            'meta_value'   => ????????,
            'compare' =>  '>=',
        );

$query = new WP_Query($args);
while($query->have_posts() ) : $query->the_post();
the_title(); ?>
endwhile; wp_reset_query();

Can you give some help?

Answer 1

Try this

$args = array(
    'post_type'   => 'book',
    'posts_per_page' => -1,
);

$query = new WP_Query($args);
while($query->have_posts() ) : $query->the_post();     
   $date = get_post_meta( get_the_ID(), 'date_all', true );
   if($date['year'] >= 2018 && $date['month'] == 3){
        the_title();
   }
endwhile; wp_reset_query();