Hide shipping methods for specific shipping class in WooCommerce

Update 2019: You should try instead this shorter, compact and effective way:

add_filter( 'woocommerce_package_rates', 'hide_shipping_method_based_on_shipping_class', 10, 2 );
function hide_shipping_method_based_on_shipping_class( $rates, $package )
{
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    // HERE define your shipping class to find
    $class = 92;

    // HERE define the shipping method to hide
    $method_key_id = 'flat_rate:7';

    // Checking in cart items
    foreach( $package['contents'] as $item ){
        // If we find the shipping class
        if( $item['data']->get_shipping_class_id() == $class ){
            unset($rates[$method_key_id]); // Remove the targeted method
            break; // Stop the loop
        }
    }
    return $rates;
}

Code goes in function.php file of your active child theme (or theme) or also in any plugin file.

Tested and works.

Sometimes, you should may be need to refresh shipping methods going to shipping areas, then disable / save and re-enable / save your "flat rates" shipping methods.

Related: Hide shipping methods for specific shipping classes in WooCommerce

To find the shipping methods IDs and the shipping classes IDs see below…

---

Update for many different shipping methods (related to your comments):

add_filter( 'woocommerce_package_rates', 'hide_shipping_method_based_on_shipping_class', 10, 2 );
function hide_shipping_method_based_on_shipping_class( $rates, $package )
{
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    // HERE define your shipping class to find
    $class = 92;

    // HERE define the shipping methods you want to hide
    $method_key_ids = array('flat_rate:7', 'local_pickup:3');

    // Checking in cart items
    foreach( $package['contents'] as $item ) {
        // If we find the shipping class
        if( $item['data']->get_shipping_class_id() == $class ){
            foreach( $method_key_ids as $method_key_id ){
                unset($rates[$method_key_id]); // Remove the targeted methods
            }
            break; // Stop the loop
        }
    }
    return $rates;
}

Tested and works…

---

Finding the shipping class ID.

1) In the database under wp_terms table:

Search for a term name or a term slug and you will get the term ID (the shipping class ID).

2) On Woocommerce shipping settings editing a "Flat rate", with your browser html inspector tool, inspect a shipping Class rate field like:

In the imput name attribute you have woocommerce_flat_rate_class_cost_64. So 64 is the ID for the shipping class.

---

Get the shipping method rate ID:

To get the related shipping methods rate IDs, something like flat_rate:12, inspect with your browser code inspector each related radio button attribute name like:

By tweaking LoicTheAztec's code (cheers), I was able to unset a shipping method for each package based on the shipping class of its contents, rather than the cart as a whole. Perhaps it will help someone else too:

// UNSET A SHIPPING METHOD FOR PACKAGE BASED ON THE SHIPPING CLASS(es) OF ITS CONTENTS
add_filter( 'woocommerce_package_rates', 'hide_shipping_method_based_on_shipping_class', 10, 2 );
function hide_shipping_method_based_on_shipping_class( $rates, $package )
{
    if ( is_admin() && ! defined( 'DOING_AJAX' ) ) {
        return;
    }

    foreach( $package['contents'] as $package_item ){ // Look at the shipping class of each item in package

        $product_id = $package_item['product_id']; // Grab product_id
        $_product   = wc_get_product( $product_id ); // Get product info using that id

        if( $_product->get_shipping_class_id() != 371 ){ // If we DON'T find this shipping class ID
            unset($rates['wbs:9:dae98e94_free_ups_ground']); // Then remove this shipping method
            break; // Stop the loop, since we've already removed the shipping method from this package
        }
    }
    return $rates;
}

This code allows me to unset my 'Free UPS Ground' shipping if the package contains anything but 'Standard' items (shipping_class_id 371 in my case).

The scenario from the original post (disable method x if shipping class y) would work like this:

// UNSET A SHIPPING METHOD FOR PACKAGE BASED ON THE SHIPPING CLASS(es) OF ITS CONTENTS
add_filter( 'woocommerce_package_rates', 'hide_shipping_method_based_on_shipping_class', 10, 2 );
function hide_shipping_method_based_on_shipping_class( $rates, $package )
{
    if ( is_admin() && ! defined( 'DOING_AJAX' ) ) {
        return;
    }

    foreach( $package['contents'] as $package_item ){ // Look at the shipping class of each item in package

        $product_id = $package_item['product_id']; // Grab product_id
        $_product   = wc_get_product( $product_id ); // Get product info using that id

        if( $_product->get_shipping_class_id() == 92 ){ // If we DO find this shipping class ID
            unset($rates['flat_rate:7']); // Then remove this shipping method
            break; // Stop the loop, since we've already removed the shipping method from this package
        }
    }
    return $rates;
}