What Is WP_Query & WordPress query functions?

As WordPress developers, we regularly need to fetch posts, pages, and other content according to specific criteria from the WordPress database. Typically, we don't have to create SQL queries because the WP_Query class and its methods provide us with a safe and proficient approach to fetch data from the database. We need to declare an array of arguments, and the WP_Query object will construct the actual SQL query.

What Is WP_Query?

WP_Query is a class given by WordPress. This WP_Query allows you to access the variables, checks, and functions which is written into that class in WordPress core without worry about writing all that code yourself. That makes your code more productive and reliable.

If you want to know how exactly WP_Query works under the hood, then you should see its code in the includes/query.php file.

In practice, WP_Query will look something like the following:

<?php
 
$args = array(
    // Arguments for your query.
);
 
// Custom query.
$query = new WP_Query( $args );
 
// Check that we have query results.
if ( $query->have_posts() ) {
 
    // Start looping over the query results.
    while ( $query->have_posts() ) {
 
        $query->the_post();
 
        // Contents of the queried post results go here.
 
    }
 
}
 
// Restore original post data.
wp_reset_postdata();
 
?>

Resetting Post Data

In the above example snippet, you can see wp_reset_postdata() after query. That is important because it resets the query back to the main query run on that page.

WP_Query to run a query in the sidebar, using wp_reset_postdata() tells to WordPress that we're still on whatever page is being seen and that it should work with the default query for that page.For instance, in case you're utilizing

On the off chance that you don't do this, some other queries on the page may break, and any conditional tags checking for what sort of page is being seen won't work.

Why Use WP_Query Over Other Methods?

WP_Query isn't the only technique for making a custom query. There are four more:

1. pre_get_posts is a hook that changes the main query. It's a productive method of changing the primary query. Anyway, you can't use it to make a new query.

2. get_posts() and get_pages() are fundamentally very similar, with the primary distinction being clear from their names. Both of these use the WP_Query class, so they are another method of doing the same thing, however, include an additional step since they call the WP_Query class rather than you doing it directly. You can use them to query either posts or pages, while WP_Query itself is all the more remarkable and lets you query nearly anything held in your database.

3. query_posts() alters the primary query yet shouldn't be used in plugins or themes. Because it tosses out the main Q and starts from the very beginning once more, replacing the primary query with another query. It may cause errors, especially with pagination, and is inefficient and will affect your page load times. If you want to modify the primary query, then you should use pre_get_posts instead, and if you need to create a new query, use WP_Query.

The diagram below, released by Andrey “Rarst” Savchenko under Creative Commons license, makes some sense of this: