Determines whether the query is the main query.

Description

For more information on this and similar theme functions, check out the Conditional Tags article in the Theme Developer Handbook.

Return

More Information

The is_main_query() function is a conditional function that can be used to evaluate whether the current query (such as within the loop) is the “main” query (as opposed to a secondary query).

This function is most commonly used within hooks to distinguish WordPress’ main query (for a page, post, or archive) from a custom/secondary query.

is_main_query() may be used with both front-end queries (theme templates, plugins, etc.), as well as admin queries. It will return true if the current query is the main query, and false if not.

Usage

if ( is_main_query() ) {
// do stuff
}

Under the Hood

This function does not accept any parameters. Instead, it automatically compares the $wp_query object (i.e., the “current query”) with the $wp_the_query object (the “main query”)

This function is an alias for the method WP_Query::is_main_query(). In filter or action hook callbacks that are passed the WP_Query object, such as ‘pre_get_posts‘, it is circular to call this function. Instead, directly call the passed object’s method. For example, if your filter callback assigns the passed WP_Query object to $query, you would call the method like so:
$query->is_main_query()

Example

add_action( 'pre_get_posts', 'foo_modify_query_exclude_category' );
function foo_modify_query_exclude_category( $query ) {
if ( ! is_admin() && $query->is_main_query() && ! $query->get( 'cat' ) )
$query->set( 'cat', '-5' );
}

Source

function is_main_query() {
	global $wp_query;

	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '6.1.0' );
		return false;
	}

	if ( 'pre_get_posts' === current_filter() ) {
		_doing_it_wrong(
			__FUNCTION__,
			sprintf(
				/* translators: 1: pre_get_posts, 2: WP_Query->is_main_query(), 3: is_main_query(), 4: Documentation URL. */
				__( 'In %1$s, use the %2$s method, not the %3$s function. See %4$s.' ),
				'<code>pre_get_posts</code>',
				'<code>WP_Query->is_main_query()</code>',
				'<code>is_main_query()</code>',
				__( 'https://developer.wordpress.org/reference/functions/is_main_query/' )
			),
			'3.7.0'
		);
	}

	return $wp_query->is_main_query();
}

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