Wordpress - How to return only certain fields using get_posts()
get_posts passes the heavy lifting off to WP_Query and if you look at the source of that class you can see that there are only a limited number of options with that fields argument. There are only three options in that switch-- ids, id=>parent, and the default case, everything.
You can use the posts_fields filter to alter what fields get returned, though it looks like you need to pass 'suppress_filters => false in the arguments in order to get that filter to run. It should look something like this:
function alter_fields_wpse_108288($fields) {
return 'ID,post_title'; // etc
}
add_filter('posts_fields','alter_fields_wpse_10888');
However, there is a larger problem. The post objects that get returned are created by a call to get_post and it doesn't honor the values passed into the original query and I don't see a way to change what gets returned either in get_posts or in the WP_Post class itself.
Have a look to this
function get_posts_fields( $args = array() ) {
$valid_fields = array(
'ID'=>'%d', 'post_author'=>'%d',
'post_type'=>'%s', 'post_mime_type'=>'%s',
'post_title'=>false, 'post_name'=>'%s',
'post_date'=>'%s', 'post_modified'=>'%s',
'menu_order'=>'%d', 'post_parent'=>'%d',
'post_excerpt'=>false, 'post_content'=>false,
'post_status'=>'%s', 'comment_status'=>false, 'ping_status'=>false,
'to_ping'=>false, 'pinged'=>false, 'comment_count'=>'%d'
);
$defaults = array(
'post_type' => 'post',
'post_status' => 'publish',
'orderby' => 'post_date',
'order' => 'DESC',
'posts_per_page' => get_option('posts_per_page'),
);
global $wpdb;
$args = wp_parse_args($args, $defaults);
$where = "";
foreach ( $valid_fields as $field => $can_query ) {
if ( isset($args[$field]) && $can_query ) {
if ( $where != "" ) $where .= " AND ";
$where .= $wpdb->prepare( $field . " = " . $can_query, $args[$field] );
}
}
if ( isset($args['search']) && is_string($args['search']) ) {
if ( $where != "" ) $where .= " AND ";
$where .= $wpdb->prepare("post_title LIKE %s", "%" . $args['search'] . "%");
}
if ( isset($args['include']) ) {
if ( is_string($args['include']) ) $args['include'] = explode(',', $args['include']);
if ( is_array($args['include']) ) {
$args['include'] = array_map('intval', $args['include']);
if ( $where != "" ) $where .= " OR ";
$where .= "ID IN (" . implode(',', $args['include'] ). ")";
}
}
if ( isset($args['exclude']) ) {
if ( is_string($args['exclude']) ) $args['exclude'] = explode(',', $args['exclude']);
if ( is_array($args['exclude']) ) {
$args['exclude'] = array_map('intval', $args['exclude']);
if ( $where != "" ) $where .= " AND ";
$where .= "ID NOT IN (" . implode(',', $args['exclude'] ). ")";
}
}
extract($args);
$iscol = false;
if ( isset($fields) ) {
if ( is_string($fields) ) $fields = explode(',', $fields);
if ( is_array($fields) ) {
$fields = array_intersect($fields, array_keys($valid_fields));
if( count($fields) == 1 ) $iscol = true;
$fields = implode(',', $fields);
}
}
if ( empty($fields) ) $fields = '*';
if ( ! in_array($orderby, $valid_fields) ) $orderby = 'post_date';
if ( ! in_array( strtoupper($order), array('ASC','DESC')) ) $order = 'DESC';
if ( ! intval($posts_per_page) && $posts_per_page != -1)
$posts_per_page = $defaults['posts_per_page'];
if ( $where == "" ) $where = "1";
$q = "SELECT $fields FROM $wpdb->posts WHERE " . $where;
$q .= " ORDER BY $orderby $order";
if ( $posts_per_page != -1) $q .= " LIMIT $posts_per_page";
return $iscol ? $wpdb->get_col($q) : $wpdb->get_results($q);
}
It's a function that mimics get_posts but with the ability to get the fields you desire. Be aware: this function is not get_posts and has 2 great limitations: run only in posts table so taxonomy and meta query cannot be run!
However, the query can rely on all the post fields and on some 'special' arguments like include, exclude and search.
The good part is this: the fields you are able to retrieve are all the field of the post table. Just pass a list or an array in the fields argument.
Bonus: passing only one field is returned a one dimensional array of strings or integers (instead of an array of objects).
List of Available args are:
$available_args = array(
'ID', // int
'post_author', // string
'post_type', // string
'post_mime_type', // string
'post_name', // string
'post_date', // string
'post_modified', // string
'menu_order', // int
'post_parent', // int
'post_status', // string
'comment_status', // string
'comment_count', // int
'orderby', // string, a valid field name
'order', // string 'ASC', or 'DESC',
'posts_per_page', // int
'include', // array (or comma separed string) of post ids
'exclude', // array (or comma separed string) of post ids
'search', // string if passed will search for it in post title
'fields', // array (or comma separed string) of fields to retrieve.
// If only 1 field is passed a 'flat' array is returned
);
Examples of usage
// Retrieve the date and the title of pages having 'Hello' in the title
$pages_hello = get_posts_fields("post_type=page&search=Hello&fields=post_date,post_title");
// another example
$args = array(
'post_type' => 'custom_post',
'posts_per_page' => -1,
'post_parent' => 1,
'include' => array(2,3,4),
'exclude' => '6,8,10',
'fields' => array('post_title', 'comment_status')
);
get_posts_fields($args);
// One more, just for fun ;)
$args = array(
'post_type' => 'attachment', 'posts_per_page' => -1,
'post_status' => 'inherit', 'fields' => 'post_mime_type'
);
foreach ( array_count_values ( get_posts_fields($args) ) as $mime => $count ) {
echo "I have $count media of the type $mime" . PHP_EOL;
}
You can only use 'ids' or 'id=>parent' for the parameter fields.
If you parse something else it will return all fields (this is default).
However, it would be nice if Wordpress could add the following 2 options: 'titles' and 'ids_and_titles'.
I am not aware of a way to parse an array for this parameter. I also think it will never happen, since the limits of the answer given by G. M.
More info: http://codex.wordpress.org/Class_Reference/WP_Query#Return_Fields_Parameter