GraphQLQueryChecker. A PHP Class that checks if a field is requested in the query. I've used this in production with webonyx/graphql-php v0.9.14 for more than a year.

GraphQLQueryChecker.php

<?php

/**
 * Instructions:
 * In an Object Resolve function, use the fourth argument ($info)
 * 
 * Example usage:
 * 
 * $fieldInQuery = GraphQLQueryChecker::isFieldInQuery('some.nested.fieldname', $info);
 * 
 * If the query looks like this:
 * 
 * query() {
 *  myObject {
 *   something
 *   some {
 *      nested {
 *        fieldname
 *      }
 *    }
 *  }
 * }
 * 
 * It will be true.
 * 
 * If it looks like this:
 * query() {
 *  myObject {
 *   something
 *   some {
 *      nested {
 *        field
 *      }
 *    }
 *  }
 * }
 * 
 * It will return false.
 * 
 * This is useful if you have some fields that are expensive to calculate
 * and want to optimize if those fields aren't requested.
 * 
 */

class GraphQLQueryChecker
{
    public static $found = false;
    public static $fields = [];

    // If you pass the $info field from a GraphQL resolve function, we can
    // recursively check the body of the passed query to determine if a
    // field is present. $fieldPath are dot separated fields. Ex: edges.node.id
    public static function isFieldInQuery($fieldPath, $info) {
        self::$fields = explode('.', $fieldPath);
        self::$found = false;
        
        foreach($info->fieldNodes as $fn) {
            if(!empty($fn->selectionSet)) {
                self::recursiveCheck(self::$fields[0], $fn->selectionSet->selections);
            }
        }
        return self::$found;
    }

    private static function recursiveCheck($field, $selections) {
        foreach($selections as $selection) {
            $nextField = self::getNextField($field);
            if($selection->name->value === $field && $nextField === null) {
                self::$found = true;
                break;
            } else if($selection->name->value === $field && !empty($selection->selectionSet)) {
                self::recursiveCheck($nextField, $selection->selectionSet->selections);
                break;
            } else if(!empty($selection->selectionSet)) {
                self::recursiveCheck($field, $selection->selectionSet->selections);
            }
        }
    }

    private static function getNextField($prevField) {
        for($i = 0; $i<count(self::$fields); $i++) {
            if($prevField === self::$fields[$i]) {
                return self::$fields[$i + 1];
            }
        }
        return false;
    }
}