WP_Query: include custom post type only with specific meta value

Question

I have the following arguments for a WP_Query:

$args = array(
    'post_type' => array( 'cpt-1', 'cpt-2' ),
    'post_status' => 'publish',
    'posts_per_page' => 9,
    'meta_query' => array(
        'relation' => 'OR',
        array(
            'key' => 'key-1',
            'compare' => 'NOT EXISTS'
        ),
        array(
            'key' => 'key-1',
            'value' => 1,
            'compare' => '!='
        )
    ),
    'tax_query' => array(
        'relation' => 'AND',
        array(
            'taxonomy' => 'ctax-1',
            'field' => 'slug',
            'terms' => 'term-1',
            'operator' => 'NOT IN'
        ),
        array(
            'taxonomy' => 'ctax-2',
            'field' => 'slug',
            'terms' => 'term-2',
            'operator' => 'NOT IN'
        )
    ),
);

Now I would like to add to the loop the custom post type cpt-3 but only if its posts has the custom field value of the custom meta key-2 set to 1.

Is it possible?

Answer 1

If the key-2 is uniquely assigned to cpt-3 post type, then you can add another meta query argument to your query arguments:

array(
    'key'     => 'key-2',
    'value'   => 1,
    'compare' => '='
)

If not, you can run another query, and then merge them as follows:

$final_query = array_merge( (array) $query_1, (array) $query_2 );

But, you should use get_posts() instead of WP_Query() since you can't merge objects with methods. The get_posts() returns an array of posts which can be merged.

However you should notice, meta queries are expensive and will slow down your website ( probably ).