如何从数组中查询Wordpress自定义字段？

I am having problems with meta_query in Wordpress. The first example works fine:

$args = array(
    'post_type' => 'my_post',
    'meta_query' => 
    array(
        array(
            'key' => 'my_field', 
            'value' => '50', 
            'compare' => 'LIKE',
        ),
    ),    
);

$query = new WP_Query( $args );

But what I want to do, as shown below, and in Wordpress documentation, does not work.

$args = array(
    'post_type' => 'my_post',
    'meta_query' => 
    array(
        array(
            'key' => 'my_field', 
            'value' => array('50','60'), 
            'compare' => 'IN',
        ),
    ),    
);

$query = new WP_Query( $args );

$args = array(
    'post_type' => 'my_post',
    'meta_query' => 
    array(
        array(
            'key' => 'my_field', 
            'value' => array(50,60), 
            'type' => 'numeric',
            'compare' => 'IN'
        ),
    ),    
);

$query = new WP_Query( $args );

I'm assuming the array('50','60') is meant to be numeric. Try removing the apostrophe and adding the proper type of numeric.