Only Allow Author To Purchase WooCommerce Products

This code restricts the purchase of products to the author of the WooCommerce product. This tutorial contains 2 separate solutions :

1. The 1st uses the woocommerce_add_to_cart_validation hook which enables you to add a custom notice
2. The 2nd uses the woocommerce_is_purchasable hook which uses the default notice.

woocommerce_add_to_cart_validation

add_filter( 'woocommerce_add_to_cart_validation', 'restrict_purchase_to_author', 10, 3 );
function restrict_purchase_to_author( $passed, $product_id, $quantity ) {
    // Get the product author (post author)
    $product_author_id = get_post_field( 'post_author', $product_id );

    // Get the current user ID
    $current_user_id = get_current_user_id();

    // Check if the current user is the author
    if ( $current_user_id != $product_author_id ) {
        // If not, prevent adding to cart and show an error message
        wc_add_notice( __( 'You are not authorized to purchase this product.', 'woocommerce' ), 'error' );
        $passed = false;
    }

    return $passed;
}

• get_post_field('post_author', $product_id): Retrieves the author (user ID) of the product.
• get_current_user_id(): Retrieves the ID of the currently logged-in user.
  woocommerce_add_to_cart_validation: WooCommerce filter hook used to validate adding a product to the cart.
• wc_add_notice(): WooCommerce function to display an error notice if the user is not authorized to purchase the product.
• $passed: Boolean variable to control whether the product can be added to the cart (true for allowed, false for not allowed).

woocommerce_is_purchasable

add_filter( 'woocommerce_is_purchasable', 'wc_restrict_purchase_to_author', 10, 2 );
function wc_restrict_purchase_to_author( $is_purchasable, $product ) {
    // Get the product author (post author)
    $product_author_id = $product->post->post_author;

    // Get the current user ID
    $current_user_id = get_current_user_id();

    // Check if the current user is the author
    if ( $current_user_id != $product_author_id ) {
        // If not, product is not purchasable
        $is_purchasable = false;
    }

    return $is_purchasable;
}

• woocommerce_is_purchasable: This filter hook is used to determine if a product is purchasable.
• $product->post->post_author: Retrieves the post author ID of the product. WooCommerce product objects store their post object, which contains the author ID.
• get_current_user_id(): Retrieves the ID of the currently logged-in user.
• $is_purchasable: Boolean variable to control whether the product is purchasable (true for purchasable, false for not purchasable).

Modify this line to target who can and cannot add the product to cart :

if ( $current_user_id != $product_author_id ) {