wp-graphql-unique-posts.php

class UniquePosts {

	protected $loaded_posts = [];
	protected $amount_requested = 0;


	public function __construct() {

		add_filter( 'graphql_connection_amount_requested', [ $this, 'filter_amount_requested' ], 10, 2 );
		add_filter( 'graphql_connection_nodes', [ $this, 'connection_nodes' ], 10, 2 );

	}

	public function filter_amount_requested( $amount_requested, $resolver ) {
		$this->amount_requested += $amount_requested;

		return $this->amount_requested;
	}

	public function connection_nodes( $nodes, $connection_resolver ) {

			if ( ! $connection_resolver instanceof \WPGraphQL\Data\Connection\PostObjectConnectionResolver ) {
				return $nodes;
			}

			if ( ! empty( $this->loaded_posts ) ) {

				$loaded_posts = $this->loaded_posts;

				$nodes = array_filter(
					$nodes,
					static function( $value, $key ) use ( $loaded_posts ) {
						return ! in_array( $value->databaseId, $loaded_posts, true );
					},
					ARRAY_FILTER_USE_BOTH
				);
			}

			array_map( function( $node ) {
				$this->loaded_posts[] = $node->databaseId;
			}, $nodes );

			return $nodes;
	}
}

add_action( 'graphql_init', function() {
	new UniquePosts();
});

This is an example of how to ensure multiple queries in the same document contain unique results.

Take this query for example:

{
  posts( first:1 ) {
    nodes {
       id
       databaseId
       title
    }
  }
  otherPosts:posts(first: 1) {
     nodes {
       id
       databaseId
       title
     }
  }
}

Default behavior for WPGraphQL will return the same post for each query:

If we wanted to ensure that multiple queries in the same GraphQL document return unique nodes, we can track the nodes that are loaded, then filter out already loaded nodes from subsequent responses.

Thus, the same query gives us unique results: