This filter applies to the posts where clause and allows you to restrict which posts will show up in various areas of the site. Combined with restrict_manage_posts it allows you to only show posts matching specific conditions.
Here is an example to match the restrict_manage_posts example:
add_filter( 'posts_where' , 'posts_where' );
function posts_where( $where ) {
if( is_admin() ) {
global $wpdb;
if ( isset( $_GET['author_restrict_posts'] ) && !empty( $_GET['author_restrict_posts'] ) && intval( $_GET['author_restrict_posts'] ) != 0 ) {
$author = intval( $_GET['author_restrict_posts'] );
$where .= " AND ID IN (SELECT object_id FROM {$wpdb->term_relationships} WHERE term_taxonomy_id=$author )";
}
}
return $where;
}
Depending on setup, if we had a custom post type of type ‘book’ with a taxonomy (category style) of type ‘author’, this filter would allow us to only show books written by a specific author.
Certain functions which retrieve posts do not run filters, so the posts_where filter functions you attach will not modify the query. To overcome this, set suppress_filters to false in the argument array passed to the function. The following code sample illustrates this.
//some function that modifies the query
function useless_condition ( $where ) { return $where . ' AND 1=1 '; }
//attach your function to the posts_where filter
add_filter( 'posts_where' , 'useless_condition' );
//get posts AND make sure filters are NOT suppressed
$posts = get_posts( array( 'suppress_filters' => FALSE ) );
Please note that the post_type query variable is not set for standard types (page, post and attachment, see WP_QUery class file line 2396 on trac), only for custom post types, so this is how you can test for each type,
add_filter( 'posts_where' , 'posts_where', 10, 2);
function posts_where( $args, $wp_query_obj ) {
$type = $wp_query_obj->query_vars['post_type'];
switch(true){
case 'any'==$type: //query any type (see codex for more details).
break;
case !empty($type) && is_array($type):
//multiple post types define
break;
case !empty($type):
//post type is a custom post.
break;
case $wp_query_obj->is_attachment():
//post type is empty but is a media.
$type='attachment';
break;
case $wp_query_obj->is_page():
//post type is empty but is a page.
$type='page';
break;
default:
//post type is empty and not an attachment nor a page, so is a post.
$type='post';
break;
}
return $where;
}
Actually the above is incomplete, post_types are not being set for taxonomy archive queries. This is a bug which has been filed on core trac,
Please note that the post_type query variable is not set for standard types (page, post and attachment, see WP_QUery class file line 2396 on trac), only for custom post types, so this is how you can test for each type,