Matt Varone - Creative Developer

— Custom fields give WordPress immense flexibility, by using them correctly you can create very complex applications with the same functionality you could only find in custom CMS. Now for us developers, one of the “problems” we might face using multiple custom fields is that there is no easy ( built in ) solution to query posts or pages based on these multiple values. If you want to do so you have to create a custom ( somewhat complex ) sql query which is clearly not an easy task for most people, and most important it ain’t a flexible solution you could just include from one project to another.

So in the look out for a nice and solid solution I came across this post by Jamie Oastler a fellow designer who was kind enough to publish this amazing function: get_post_meta_multiple.
I really encourage you to go ahead and read his post as he makes an excellent and clear explanation of how the function works and how to implement it in your project.

As good as it is, I found that I still needed a bit more flexibility to use it in my projects so I went ahead and made a few small improvements that others might find useful. These give you the option to make your query even more specific, you can:

1. Select whether you want to retrieve only posts or pages.
2. Pass a number ( or many numbers ) to select posts only from specific categories.
3. Limit the number of posts you want to retrieve.

Usage Example

The usage of the function is really simple, as stated before Jamie made an excellent explanation on his blog, so no need to repeat all of that here again. The three new values I added can be assigned easily when calling the function as you can find in the example bellow:

<?php

/*
Function variables:

$aMetaDataList(array) example: array('meta_key' => 'meta_value','meta_key_2' => 'meta_value_2 )
$szType(string) = "post" or "page"
$szCategory(string) = example: '1' or '1,2,3'
$iLimit(integer)
*/

$aMetaDataList = array(
'custom_field_name_1' => 'Yes',
'custom_field_name_2' =>'No',
// etc…
);

$szCategory = '3'; // posts only from category 3
$iLimit = 6; // get only 6 posts

$my_posts = get_post_meta_multiple( $aMetaDataList, 'post', $szCategory, $iLimit );

// Once you have the posts just loop trough them as you would do usually

if ($my_posts):
foreach( $my_posts as $post ):

setup_postdata($post);

the_title();

endforeach;
endif;

?>

As you can see its very easy to use and it gives us developers huge flexibility to create amazing stuff. Props to Jamie for his great work. Hope you found this useful, if you have any suggestions please feel free to leave it on the comments, thank you!

The Function

<?php
function get_post_meta_multiple( $aMetaDataList = array(), $szType = 'post', $szCategory = NULL, $iLimit = NULL )
{
global $wpdb;

$szQuerystr = "SELECT p.* FROM $wpdb->posts AS p";

if ( $szCategory != NULL AND is_string($szCategory) )
{
$szQuerystr .= " LEFT JOIN $wpdb->term_relationships ON (p.ID = $wpdb->term_relationships.object_id) ";
$szQuerystr .= " LEFT JOIN $wpdb->term_taxonomy ON ($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id) ";
}

$szQuerystr .=  "WHERE p.ID IN ( ";

$szQuerystr .= "SELECT post_id FROM $wpdb->postmeta WHERE ";

$aInnerqry = array();

foreach($aMetaDataList as $szKey => $szValue)
{
$aInnerqry[] = $wpdb->prepare( "(meta_key = %s AND meta_value = %s)", $szKey, $szValue );
}

$szQuerystr .= implode(" OR ", $aInnerqry);

$szQuerystr .= " GROUP BY post_id ";
$szQuerystr .= "HAVING count(*) = " . count($aMetaDataList);

$szQuerystr .= ") AND p.post_status = 'publish' AND p.post_type = '".$szType."'";

if ( $szCategory != NULL AND is_string($szCategory) )
$szQuerystr .= " AND $wpdb->term_taxonomy.term_id IN(".$szCategory.")";

$szQuerystr .= " ORDER BY p.post_title ASC";

if ( $iLimit != NULL AND is_int($iLimit) )
$szQuerystr .= " LIMIT ".$iLimit;

$aMetaResults = $wpdb->get_results($szQuerystr, OBJECT);

return $aMetaResults;
}
?>