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In wp_query object, the wordpress db tables are queried. But not all db tables are queried everytime.
For example, if i am on blog index page, it will query only the posts db table to display the list of posts.
What if i want to display the only those posts that have specific meta value for a specific meta key?
Another example can be in search pages: say, what if we want to search only the posts that have some specific meta value for a given meta key ?
obviously we will require to alter the where clause of the wp_query object to include meta key and meta value conditions, but , the search results will have no value, if the postmeta db table is not included in the table list.
to include the db tables in the query, we use 'posts_join' filter.
an example can be seen below:
//join for searching metadata function AIOThemes_joinPOSTMETA_to_WPQuery($join) { global $wp_query, $wpdb;
if (!empty($wp_query->query_vars['s'])) {
$join .= "LEFT JOIN $wpdb->postmeta ON $wpdb->posts.ID = $wpdb->postmeta.post_id "; }
return $join; } add_filter('posts_join', 'AIOThemes_joinPOSTMETA_to_WPQuery');
and to make the specific search, we might use the code similar to the following:
function AIO_AlphabeticSearch_WhereString( $where, &$wp_query )
{
global $wpdb;
if(isset($_GET['aioAlphaSearchMode']) && $_GET['aioAlphaSearchMode'] == 1){
$searchAlphabet = $_GET['s'];
$where .= ' AND ' . $wpdb->posts . '.post_title LIKE \.$searchAlphabet.'%\' ';
// use only if the post meta db table has been joined to the search tables using posts_join filter $where .= " AND ($wpdb->postmeta.meta_key = 'JDReview_CustomFields_ReivewOrNewsPostType' AND $wpdb->postmeta.meta_value = 'JDReview_PostType_ReviewPost') ";
}
add_filter( 'posts_where', 'AIO_AlphabeticSearch_WhereString', 10, 2 );
