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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.
<?php
//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 ) );
?>