Using pre_get_posts to Modify Queries for Meta Data and More

There are a lot of ways to query posts in WordPress and a lot of parameters you can use for pulling in just the data you want. For example, you can easily pull in just posts that are in category X, Y, or Z, and you can also just as easily pull in only posts that have a particular meta field set to some value or other. This tutorial video is going to focus on demonstrating the correct way to modify queries and also show how to easily query posts based on meta fields.

One of the worst mistakes that many, many developers make (I’ve been guilty of it countless times) is using query_posts() to modify the main query. One particular example I can think of is using query_posts() in search.php to modify the search results.

Another “crime” that a lot of developers, myself included, are guilty of is modifying queries with a disregard for other queries that might be running on the page. For example, a lot of theme developers like to add an option to their admins for controlling the number of posts displayed on archive pages. A lot of times what happens here is the custom posts_per_page parameter the developer sets overrides ALL queries on the page. I’ve seen this happen several times with my Sugar FAQs plugin; the posts_per_page parameter set by the theme overrides the posts_per_page set in the get_posts() query for the FAQs, so instead of showing 15 questions, the short code only shows 5.

There are many other “crimes” that get committed when queries are involved, but we don’t need to go through. Suffice it to say that the correct way to modify queries anywhere on your WordPress site is through the pre_get_posts action hook (also available as a filter).

Discussed in depth in the video, the pre_get_posts action allows us to easily modify queries anywhere on the site. Here is a quick example of how to force the front page to only show posts that have a meta key called “ecpt_color” that is set to a value of “green”.

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function pw_filter_query( $query ) {
 
	if( is_front_page() && is_main_query() && $query->query_vars['post_type'] != 'nav_menu_item' ) {
 
 
		$query->set('meta_key', 'ecpt_color');
		$query->set('meta_value', 'green');
 
	}
 
}
add_action('pre_get_posts', 'pw_filter_query', 9999);