Check if specific Order metadata or order item metadata exist in WooCommerce

We're working on updating some custom plugins to HPOS. I've looked at https://developer.woocommerce.com/docs/hpos-order-querying-apis/ for the answer and it didn't seem to have it.

I'm looking for code to determine if Order Meta Data exists. Something similar to metadata_exists().

Is there code to determine if the key exists in wp_wc_orders_meta table?

How about determining if the key exists in the wp_woocommerce_order_itemmeta table?

Finally, would just getting the data with $order->get_meta('my_stuff') execute about as fast then reviewing what is returned? Sometimes a 4 or 5-data array is the value. I'm thinking that nowadays that the executions are so rapid that maybe just getting the values would be as fast - it's the memory that would increase a bit. Is this not a concern these days? Your thoughts?

if (empty(metadata_exists('post', $order_id, 'some_order_meta_tag'))) {
    $my_metadata_exists = 0;
}

To check for WooCommerce order metadata or order item metadata, you can use the following WC_Data methods from an existing WC_Order object (compatible with High Performance Order Storage HPOS):

1. meta_exists( $key = '' ) method (the most efficient way),
2. get_meta( $key = '', $single = true, $context = 'view' ) method, (alternative).

You can replace in the examples below 'desired_meta_key' with the desired meta-key:

1. Usage examples for meta_exists() method:

## For order metadata

// check if metadata exists
if ( $order->meta_exists( 'desired_meta_key' ) ) {
   // Do something
}

## For order item metadata

// Get order items (line items)
$line_items = $order->get_items();

// Loop through order items
foreach ( $line_items as $item ) {
    // check if metadata exists
    if ( $order->meta_exists( 'desired_meta_key' ) ) {
       // Do something
    }
}

2. Usage examples for get_meta() method:

## For order metadata

// Get specific metadata if it exists and is not empty
if ( $metadata = $order->get_meta( 'desired_meta_key' ) ) {
   // Do something with this existiong $metadata
}

## For order item metadata

// Get order items (line items)
$line_items = $order->get_items();

// Loop through order items
foreach ( $line_items as $item ) {
    // Get specific metadata if it exists and is not empty
    if ( $metadata = $order->get_meta( 'desired_meta_key' ) ) {
       // Do something with this existiong $metadata
    }
}

Works with or without HPOS enabled...

Since WooCommerce version 3, note that all those WC_Data methods work on WooCommerce CRUD object classes, like on WC_Order, WC_Order_Item, WC_Product, WC_Coupon, WC_Customer, etc…

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Additions:

To be sure that $order variable exist and is a WC_Order object, you can use (at least with a valid Order ID):

if ( ! is_a( $order, 'WC_Order' ) && $order_id > 0 ) {
   // Get the WC_Order object from an existing order ID
    $order = wc_get_order( $order_id );
}

if ( is_a( $order, 'WC_Order' ) ) {
   // Your code using $order variable
}

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To check if HPOS is enabled you can use the following custom conditional function:

## Conditional function: Check if HPOS is enabled

use Automattic\WooCommerce\Utilities\OrderUtil;

function is_hpos() {
    return OrderUtil::custom_orders_table_usage_is_enabled();
}

Like in this example:

if ( is_hpos() ) {
   // HPOS is enabled
} else {
   // HPOS is disabled
}