Filtering posts by post meta data

Question

I want to filter posts in such a way that only posts, for which get_post_meta($post->ID, "project_cat", true) (it returns a post ID) is equal to my specified value, are shown.

Any way to do this?

I am especially interested in ways to do it compatible with WP-Paginate plugin.

Answer 1

The WP_Query object accepts a post meta argument. Generally speaking you want to do the following:

$my_query = new WP_Query(array(
    'post_type' => 'post',
    'meta_query' => array(
                     array(
                      'key' => 'project_cat',
                      'value' => 'my-value',
                      )
                    ),
     //Other query properties
));

Where 'my-value' is your 'specified value'.

Example usage: (untested)

add_action('pre_get_posts','my_pre_get_posts')

funciton my_pre_get_posts($query){

    //Check this is main query and other conditionals as needed
    if($query->is_main_query()){
        $query->set('meta_query', array(array(
                                      'key' => 'project_cat',
                                      'value' => 'my-value'))
                                     );
    }
}

See WP_Query, pre_get_posts. All conditionals are available to you. Currently this runs on every main query - which you probably don't want.

Alternatively you can use query_posts (a simpler, but much less efficient way) to alter the query for only a specific instance in a template.