Creating dropdown with Woocommerce products and automatically add product to cart based on selection

Question

Using Products dropdown from same category inside Woocommerce product short description answer code, I managed to create a products dropdown in WooCommerce.

On the <select> tag I wanted to call a php function which adds the product to the cart based on the selected option from dropdown.

I changed in the code the <select> tag with the following:

<select name="products-select" id="products-select" onchange="'.add_to_cart().'">

Php function to add woocommerce products to cart:

function add_to_cart(){
    WC()->cart->add_to_cart( 1147 ); 
}

For some reason the function is called when I load the page.

Answer 1

To get a dropdown of related products from same product category that can be added to cart, It requires to use javascript making some changes in the code like:

add_shortcode( 'products_dropdown', 'wc_products_from_cat_dropdown' );
function wc_products_from_cat_dropdown( $atts ) {
    // Shortcode Attributes
    $atts = shortcode_atts( array(
        'product_id' => '',
    ), $atts, 'products_dropdown' );

    $product_id = is_product() ? get_the_id() : $atts['product_id'];

    if ( empty($product_id) )
        return;

    ob_start();

    $query = new WP_Query( array(
        'post_type'      => 'product',
        'post_status'    => 'publish',
        'posts_per_page' => '-1',
        'post__not_in'     => array( $product_id ),
        'tax_query' => array( array(
                'taxonomy' => 'product_cat',
                'field'    => 'term_id',
                'terms'    => wp_get_post_terms( $product_id, 'product_cat', array( 'fields' => 'ids' ) ),
            ),
            array(
                'taxonomy' => 'product_type',
                'field'    => 'name',
                'terms'    => 'simple',
        ) ),
    ) );

    if ( $query->have_posts() ) :

    echo '<div class="products-dropdown"><select name="products-select" id="products-select">
    <option value="">'.__('Choose a related product').'</option>';

    while ( $query->have_posts() ) : $query->the_post();

    $type = wp_get_post_terms( get_the_ID(), 'product_type', ['fields','slug'] );
    print_pr($type);

    echo '<option value="?add-to-cart='.get_the_ID().'">'.get_the_title().'</option>';

    endwhile;

    echo '</select><br><a class="button disabled" href="">'.__("add to cart").'</a></div>';

    wp_reset_postdata();

    endif;

    ?>
    <script type='text/javascript'>
        jQuery(function($){
            var a = '.products-dropdown', b = a+' .button', d = 'disabled', s = a+' select';
            $(document.body).on('change', s, function(){
                var qv = $(this).val();
                $(b).attr('href', qv);
                if ( qv != '' ) {
                    $(b).removeClass(d).attr('href', $(this).val());
                } else if ( qv == '' && ! $(b).hasClass(d) ) {
                    $(b).addClass(d);
                }
            }).on('click', b, function(e){
                if ( $(b).attr('href') == '' ) {
                    e.preventDefault();
                }
            });

        });
    </script>
    <?php

    return ob_get_clean();
}

Code goes in functions.php file of the active child theme (or active theme). Tested and works.

The code will show a dropdown of simple products (from same product category(ies)) that with an add to cart button.

---

USAGE

1). For single product pages: Just paste the following shortcode in the product short description (or descrition):

[products_dropdown]

2). For single product pages, inside php code:

echo do_shortcode("[products_dropdown]");

3). on any post or page within the text editor, define the product_id argument (below the defined product id is 37 ) :

[products_dropdown product_id="37"]

---

The add to cart button is disabled until a product is selected:

When a product is selected in the dropdown, the add to cart button get activated, and the selected product can be added to cart: