WordPress Plugin Development- When our plugin functions call?

Question

Assume that I have created plugin to include custom post type called site and plugin to search result. Assume I have added only following code to my plugin.

function searchAll( $query ) {
 if ( $query->is_search ) { $query->set( 'post_type', array( 'site', 'plugin' )); } 
 return $query;
}
add_filter( 'the_search_query', 'searchAll' );

When this function call? Is it call in every page views? Or is it call in only when some one search?

Answer 1

You've hooked into a filter. The code will run when that filter is executed. In your case, that is when the_search_query() function runs:

2595    /**
2596     * Display the contents of the search query variable.
2597     *
2598     * The search query string is passed through {@link esc_attr()}
2599     * to ensure that it is safe for placing in an html attribute.
2600     *
2601     * @since 2.1.0
2602     */
2603    function the_search_query() {
2604            /**
2605             * Filter the contents of the search query variable for display.
2606             *
2607             * @since 2.3.0
2608             *
2609             * @param mixed $search Contents of the search query variable.
2610             */
2611            echo esc_attr( apply_filters( 'the_search_query', get_search_query( false ) ) );
2612    }

WordPress core only runs that function a few times (you can grep your source to find it) but themes and plugins may run it as well.