Need help with Interface Types

[Poolshark]

Hi, me again ... ;)

I'm trying to get Interface Types working but it seems that the documentation of how to do that is still missing in the docs. Therefore, I've gone through the source and tried to understand how you have implemented GraphQL Interfaces for WP GraphQL (e.g. CommenterInterface with CommentAuthor object type).

I have tried the following:

Register the Object Type

register_graphql_object_type( 'MyType', [
    'description' => 'This is an object type with interface',
    'interfaces' => ['MyInterface'],
    'fields' => [
        'one' => [
            'type' => 'Integer',
            'description' => 'A field of type Integer'
        ]
    ]
 ]);

Register the Interface Type

register_graphql_interface_type( 'MyInterface', [
    'description' => 'This is a GraphQL interface type',
    'resolveType' => function( $data ) use ( $typeRegistry ) {
        // I'm not sure what to do here, so I just return the Object Type 'MyType'
       return 'MyType';
    } ,
    'fields' => [
        'message' => [
            'type' => ['non_null' => 'String'],
            'description' => 'This is a mandatory message'
        ]
    ] 
]);

Register a Custom Field

register_graphql_field('RootQuery', 'MyCustomField', [
    'type' => 'MyType',
    'description' => 'This is a custom field',
    'resolve' => function () {
         return [ 'one' => 1, message = 'This needs to be said!' ];
    }
]);

The Query

query MyQuery {
  myCustomField {
    one
    message  <-- does not appear in the schema and I therefore get an error if I want to query it
  }
}

I can query the field one fine but I get no error that I have to query the field message. If I manually add message to MyType I can basically do what I want with this field (e.g. make it type Integer and not mandatory). Should I not get some sort of error along the way?

Thanks!

[jasonbahl]

Hey @Poolshark I realize I'm pretty late to replying here. Possibly there was a bug in the version you tried this with, but on WPGraphQL v1.6.10 I'm able to use your code and query what you were querying and get the data from the response.

Here's the code exactly as I have it:

add_action( 'graphql_register_types', function( $type_registry ) {

	register_graphql_object_type( 'MyType', [
		'description' => 'This is an object type with interface',
		'interfaces' => ['MyInterface'],
		'fields' => [
			'one' => [
				'type' => 'Integer',
				'description' => 'A field of type Integer'
			]
		]
	]);

	register_graphql_interface_type( 'MyInterface', [
		'description' => 'This is a GraphQL interface type',
		'resolveType' => function( $data ) use ( $type_registry ) {
			// I'm not sure what to do here, so I just return the Object Type 'MyType'
			return 'MyType';
		} ,
		'fields' => [
			'message' => [
				'type' => ['non_null' => 'String'],
				'description' => 'This is a mandatory message'
			]
		]
	]);

	register_graphql_field('RootQuery', 'MyCustomField', [
		'type' => 'MyType',
		'description' => 'This is a custom field',
		'resolve' => function () {
			return [ 'one' => 1, 'message' => 'This needs to be said!' ];
		}
	]);

} );

And in GraphiQL I can query:

{
  myCustomField {
    one
    message
  }
}

![Screen Shot 2021-12-10 at 2 01 25 AM](https://user-images.githubusercontent.com/1260765/145546805-1cbd0801-2007-42e1-8f53-888a54392a85.png

And I can also see MyType in the Schema docs with MyInterface implemented on the type, and both message and one fields on MyType.

)