How to extend admin search in WP edit page using either post id or custom fields?

To extend the WordPress admin search to include post ID or custom fields, you’ll need to add custom code to your theme’s functions.php file or a custom plugin. This involves hooking into WordPress’s query modification filters.

Here’s a PHP code snippet that demonstrates how to achieve this.

<?php
/**
 * Plugin Name: Custom Admin Search Extension
 * Description: Extends the WordPress admin search to include Post ID and Custom Fields.
 * Version: 1.0
 * Author: Your Name
 */

/**
 * Filter the posts query in the admin area to include custom search parameters.
 * This function hooks into 'pre_get_posts' to modify the main query.
 *
 * @param WP_Query $query The WP_Query instance (passed by reference).
 */
function custom_admin_search_extend( $query ) {
    // Only proceed if it's the main query in the admin area and a search term is present.
    if ( ! is_admin() || ! $query->is_main_query() || ! $query->get( 's' ) ) {
        return;
    }

    // Get the search term.
    $search_term = $query->get( 's' );

    // Remove the default 's' parameter to prevent conflicts with our custom logic.
    $query->set( 's', '' );

    // Initialize an array for custom WHERE clauses.
    $custom_where = array();

    // 1. Search by Post ID
    // Check if the search term is a numeric ID.
    if ( is_numeric( $search_term ) ) {
        $custom_where[] = "ID = '" . intval( $search_term ) . "'";
    }

    // 2. Search by Custom Fields (Meta Data)
    // You can add multiple custom fields to search here.
    // Example: Searching 'my_custom_field' and 'another_field'.
    $custom_fields_to_search = array( 'my_custom_field', 'another_field' ); // <-- Customize your custom field keys here

    foreach ( $custom_fields_to_search as $field_key ) {
        $custom_where[] = "EXISTS (
            SELECT 1 FROM " . $query->query_vars['posts_per_page'] . "postmeta
            WHERE post_id = " . $query->query_vars['posts_per_page'] . "posts.ID
            AND meta_key = '" . esc_sql( $field_key ) . "'
            AND meta_value LIKE '%" . esc_sql( $search_term ) . "%'
        )";
    }

    // Combine the default post title/content search with custom fields search.
    // This ensures the standard search still works alongside custom fields.
    $search_query = array();
    $search_query[] = "(
        " . $query->query_vars['posts_per_page'] . "posts.post_title LIKE '%" . esc_sql( $search_term ) . "%' OR
        " . $query->query_vars['posts_per_page'] . "posts.post_content LIKE '%" . esc_sql( $search_term ) . "%'
    )";

    // Add custom WHERE clauses if any were generated.
    if ( ! empty( $custom_where ) ) {
        $search_query[] = "(" . implode( ' OR ', $custom_where ) . ")";
    }

    // Combine all search parts with OR logic.
    $final_search_sql = implode( ' OR ', $search_query );

    // Modify the WHERE clause of the main query.
    // We use 'posts_where' filter to inject our custom SQL.
    add_filter( 'posts_where', function( $where ) use ( $final_search_sql ) {
        // Ensure our custom search is added to the existing WHERE clause.
        // If there's an existing search, combine them.
        if ( ! empty( $final_search_sql ) ) {
            $where = ' AND (' . $final_search_sql . ')';
        }
        return $where;
    }, 10, 1 ); // Priority 10, accepts 1 argument.
}
add_action( 'pre_get_posts', 'custom_admin_search_extend' );

/**
 * Adjust the JOIN clause if searching custom fields to ensure postmeta table is joined.
 * This is crucial for the custom field search to work.
 *
 * @param string $join The JOIN clause of the query.
 * @param WP_Query $query The WP_Query instance.
 * @return string The modified JOIN clause.
 */
function custom_admin_search_join( $join, $query ) {
    // Only apply if it's the main admin query and a search term is present.
    if ( ! is_admin() || ! $query->is_main_query() || ! $query->get( 's' ) ) {
        return $join;
    }

    global $wpdb;
    // Ensure the postmeta table is joined if not already.
    // This prevents duplicate joins if other plugins also join postmeta.
    if ( strpos( $join, $wpdb->postmeta ) === false ) {
        $join .= " LEFT JOIN {$wpdb->postmeta} ON {$wpdb->posts}.ID = {$wpdb->postmeta}.post_id";
    }
    return $join;
}
add_filter( 'posts_join', 'custom_admin_search_join', 10, 2 );

/**
 * Ensure distinct results when joining the postmeta table,
 * as a post might have multiple meta entries matching the search.
 *
 * @param string $distinct The DISTINCT clause of the query.
 * @param WP_Query $query The WP_Query instance.
 * @return string The modified DISTINCT clause.
 */
function custom_admin_search_distinct( $distinct, $query ) {
    // Only apply if it's the main admin query and a search term is present.
    if ( ! is_admin() || ! $query->is_main_query() || ! $query->get( 's' ) ) {
        return $distinct;
    }

    return 'DISTINCT';
}
add_filter( 'posts_distinct', 'custom_admin_search_distinct', 10, 2 );

This PHP code provides a robust way to extend the WordPress admin search.

How to use this code:

1. Create a new file (e.g., custom-admin-search.php) in your WordPress wp-content/plugins/ directory.
2. Copy and paste the entire code block into this new file.
3. Activate the plugin from your WordPress admin dashboard under “Plugins.”
4. Customize: In the custom_admin_search_extend function, locate the line: $custom_fields_to_search = array( ‘my_custom_field’, ‘another_field’ ); Replace ‘my_custom_field’ and ‘another_field’ with the actual keys of the custom fields you want to include in the search. You can add as many as you need.

Explanation of the Code:

• custom_admin_search_extend( $query ): This is the main function hooked into pre_get_posts. This hook allows us to modify the WP_Query object before it executes the database query.
  • It first checks if it’s an admin request, the main query, and if a search term (s) is present.
  • It then retrieves the search term and clears the default s parameter to prevent WordPress from applying its default search logic, giving us full control.
  • Post ID Search: It checks if the search term is purely numeric. If so, it adds a condition to search by ID.
  • Custom Fields Search: It iterates through a defined array of custom field keys ($custom_fields_to_search). For each field, it constructs a LIKE clause to search within the meta_value of the wp_postmeta table.
  • Combining Search: It combines the standard post title/content search with the custom field and post ID searches using OR logic.
  • posts_where filter: This filter is used to inject our custom SQL WHERE clause into the main query.
• custom_admin_search_join( $join, $query ): This function is hooked into posts_join. It ensures that the wp_postmeta table is LEFT JOINed to the wp_posts table. This is essential because custom field data is stored in wp_postmeta, and without this join, the custom field search conditions would fail.
• custom_admin_search_distinct( $distinct, $query ): This function is hooked into posts_distinct. When joining the wp_postmeta table, a single post might have multiple meta entries that match the search, leading to duplicate results. Adding DISTINCT ensures that each post appears only once in the search results.

This approach is flexible and allows you to easily add more custom fields to the search criteria by simply updating the $custom_fields_to_search array.