A better way of getting draft posts that has a particular post meta using get_posts function

You can use the post meta arguments that get_posts function already supports. So, there is no need to use get_post_meta function in a PHP loop.

For your use case, post meta related arguments can be used in one of the two possible ways:

1. Either using meta_key, meta_value, meta_compare arguments;

2. Or, using the meta_query argument which supports an array of different post meta checks and hence is more powerful.

Using any of these methods returns all the necessary post data in one go.

Method-1:

The following example uses meta_key, meta_value, meta_compare arguments to achieve what you want:

function karma_get_pre_publish_posts() {
    $args = array(
        'post_type'    => 'post',
        'post_status'  => 'draft',
        'meta_key'     => 'approve',
        'meta_value'   => 'pre-publish',
        'meta_compare' => '='
    );

    return get_posts( $args );
}

Method-2:

The meta_query argument on the other hand requires an array of one or more argument arrays to query the posts with related post meta.

Like this:

function karma_get_pre_publish_posts() {
    // Yes, $meta_query argument has to be coded as an array of arrays.
    $meta_query = array(
        array(
            'key' => 'approve',
            'value' => 'pre-publish',
            'compare' => '='
        )
    );
    $args = array(
        'post_type' => 'post',
        'post_status' => 'draft',
        'meta_query' => $meta_query
    );

    return get_posts( $args );
}

Further reading:

• Post meta related arguments (or parameters) of the get_posts function come from the parse_query method of WP_Query class. You may check the parse_query method documentation for more details.

• Also, since the internal implementation related to post meta arguments is using the WP_Meta_Query class, you will also find some details in WP_Meta_Query class and WP_Meta_query constructor documentations.

There are user contributed examples in these documentations with more advanced use cases, including multiple post meta comparisons in a single query.