Adding Variables to post query

Question

How do I add custom variables to the wordpress query without having to hit the database twice. In the example below I want to add some meta filters. All this code works fine but I have been running query_posts() to execute it. I want to be able to add to the query before it is run by default so I don't have to query the db twice.

In this I was hoping if I modify $wp_query->query before it is executed my changes would be added to the query. The query is being changed fine, just not the output. Any ideas? Thanks.

add_action('pre_get_posts', 'my_custom_query'); 
function my_custom_query(){

if(isset($_SESSION['size']) && $_SESSION['size'] != 'all'){
    $cfilter[] = array( 'key' => 'cc_size', 'value' => $_SESSION['size'] );
}

if(isset($_SESSION['gender']) && $_SESSION['gender'] != 'all'){
    $cfilter[] = array( 'key' => 'cc_gender', 'value' => $_SESSION['gender'] );
}


$extraArgs = array(
    'orderby' => 'post-title',
    'paged' => get_query_var('paged')
);


if(!empty($cfilter)){ $extraArgs['meta_query'] = $cfilter; }

global $wp_query;
$wp_query->query = array_merge( $wp_query->query, $extraArgs );

}

Answer 1

As toscho said, you can modify the query in the pre_get_posts hook. That hook gets the query object passed as an argument, so you don't have to read a global variable.

add_action( 'pre_get_posts', 'wpse12692_pre_get_posts' ); 
function wpse12692_pre_get_posts( &$wp_query )
{
    if( isset( $_SESSION['size'] ) && $_SESSION['size'] != 'all' )
    {
        $wp_query->query_vars['meta_query'] = array(
            'key' => 'cc_size',
            'value' => $_SESSION['size'],
        );
    }

    if( isset( $_SESSION['gender'] ) && $_SESSION['gender'] != 'all' )
    {
        $wp_query->query_vars['meta_query'] = array(
            'key' => 'cc_gender',
            'value' => $_SESSION['gender'],
        );
    }

    $wp_query->query_vars['orderby'] = 'post-title';
    // The next line is redundant, get_query_vars reads it from the global $wp_query object
    $wp_query->query_vars['paged'] = get_query_var('paged');
}

I see that your query depends on session variables. This can make it harder to forward a link to a page to someone else. Have you considered putting this in the URL and reading it from there? You can do that by creating extra rewrite rules.

Answer 2

Hook into the action 'pre_get_posts'.
Example:

add_action( 'pre_get_posts', 'no_sticky_on_front' );

function no_sticky_on_front()
{
    is_front_page() and $GLOBALS['wp_query']->query_vars['ignore_sticky_posts'] = TRUE;
}