Add Product Bundles to Your WooCommerce GraphQL API

Introduction

This tutorial is to show you how to add the WooCommerce Product Bundle product type to your WooCommerce GraphQL API. This is definitely a work-in-progress that I'll try and keep updated.

The two plugins in use here are: 1. WPGraphQL: 0.10.2 2. WPGraphQL WooCommerce (WooGraphQL): 0.5.1

Begin with the end in mind

Ideally, this is the shape of the GraphQL query that we're shooting for:

query {
  products {
    name
    shortDescription
    ...on BundleProduct {
      price
      bundledItems {
        node {
          name
          shortDescription
        }
      }
    }
  }
}

TLDR - the final code

Check out the gist for the full implementation: https://gist.github.com/jacobarriola/5d055ba102c001f0c556427a1ae78cd2

Here are the high level steps that I intend to take:

1. Register the BundleProduct ObjectType
2. Register a RootQuery field for the new ObjectType
3. Expose the new BundleProduct object type to WooCommerce GraphQL's list of product types
4. Expose the new BundleProduct to the product types enum values so that query input filters will work
5. Add fields to the BundleProduct ObjectType
6. Create a Connection to expose bundleItems to BundleProduct

Product is a GraphQL Interface

An important WooCommerce GraphQL architectural concept to grasp is that a Product is an Interface type and all product_types (simple, variable, external, grouped) are implementations of the Product Interface.

📕 Say what?! Check out the GraphQL docs on what an Interface is: https://graphql.org/learn/schema/#interfaces

In normal WooCommerce-land, product_types (simple, variable, external, grouped) are simply terms for the product_type custom taxonomy. The Product Bundle add-on extends this same pattern by creating a term bundle for the product_type taxonomy.

Therefore, in order to add product bundles to our GraphQL API, we're going to follow the same implementation pattern that the core product types already follow in WooGraphQL and implement and Product interface.

Step one: add the bundle product type to GraphQL product types

This filter allows us to safely add our bundle product type. The underlying method uses this list to expose the WooCommerce product types (simple, variable, external, grouped) to the GraphQL schema.

add_filter( 'graphql_woocommerce_product_types', function ( $product_types ) {
	$product_types['bundle'] = 'BundleProduct';
	
	return $product_types;
} );

Step two: add the BundleProduct ObjectType to the GraphQL TypeRegistry

This is the meat of our customization. We're bascially declaring our new Type along with all of the fields.

add_action( 'graphql_register_types', function () {
	
	/**
   * Register BundleProduct ObjectType
   */
	register_graphql_object_type( 'BundleProduct', [
			'description' => 'A product bundle object',
			'interfaces'  => [ 'Node', 'Product' ], // Following same pattern that other product types declare
			'fields'      =>
				[
					'bundlePriceMin' => [
						'type'    => 'String',
						'resolve' => function ( $source ) {
							return $source->get_bundle_price('min');
						}
					],
					'bundlePriceMax' => [
						'type'    => 'String',
						'resolve' => function ( $source ) {
							return $source->get_bundle_price('max');
						}
					],
					'groupMode'=> [
						'type'    => 'String',
						'resolve' => function ( $source ) {
							return $source->get_group_mode();
						}
					],
					'price' => [
						'type'    => 'String',
						'resolve' => function ( $source ) {
							return $source->get_price();
						},
					],
					'salePrice' => [
						'type'    => 'String',
						'resolve' => function ( $source ) {
							return $source->get_sale_price();
						},
					],
					'regularPrice' => [
						'type'    => 'String',
						'resolve' => function ( $source ) {
							return $source->get_regular_price();
						},
					],
					'bundledItems' => [
						'type'    => 'String',
						'resolve' => function ( $source ) {
							return 'this is still a work-in-progress';
						},
					],
				],
		]
	);
} );

Why are product bundle methods available?

By default, the first parameter in a field resolver is always the latest thing that was queried. In our case, we are querying Product types because of the Product interface; therefore, the $source parameter is an instance of the WPGraphQL\WooCommerce\Model\Product class.

But if you explore the class, you won't find any of the Product Bundle methods I'm using (ie get_bundle_price()). But why isn't PHP throwing any fatal cannot find get_bundle_price() method in ... errors? This is because the presence of a __call() magic PHP method in the parent class (WPGraphQL\WooCommerce\Model\Crud_CPT), which allows us to call dynamic or inaccessible methods that are not definded in the class.

Step three: register a GraphQL field with our new Type

The Type will not appear on our GraphQL API until we register at least one field. For now, I'm registering a RootQuery so that consumer can query bundleProduct directly like the other product types.

add_action( 'graphql_register_types', function () {
  
  register_graphql_field(
      'RootQuery',
      'bundleProduct',
      [
        'type' => TYPE_BUNDLE_PRODUCT,
      ]
  );
});

Step four: add bundle to the product types enum

Doing so will include our new BundleProduct to be included in the where argument when querying products.

add_filter( 'graphql_product_types_enum_values', function ( $values ) {
	$values['BUNDLE'] = [
		'value'       => 'bundle',
		'description' => 'A bundle product',
	];
	
	return $values;
} );

Step five (TBD): create a new Connection in order to return bundle items

In my query, I'd like to be able to return the actual items that are part of the product bundle. In WooCommerce-land, these are known as bundleItems. This is still a work-in-progress.

Conclusion

Still more work here, but hopefully this will get you started. There's still plenty to be done, such as: 1. add bundle items 2. add bundle to the cart 3. more that I haven't thought of 🤷🏽‍♂️