ApiPlatform\Core\Bridge\Symfony\Routing\OperationMethodResolver::getOperationMethod PHP Method

    private function getOperationMethod(string $resourceClass, string $operationName, bool $collection) : string
    {
        $resourceMetadata = $this->resourceMetadataFactory->create($resourceClass);
        if ($collection) {
            $method = $resourceMetadata->getCollectionOperationAttribute($operationName, 'method');
        } else {
            $method = $resourceMetadata->getItemOperationAttribute($operationName, 'method');
        }
        if (null !== $method) {
            return $method;
        }
        if (null === ($routeName = $this->getRouteName($resourceMetadata, $operationName, $collection))) {
            throw new RuntimeException(sprintf('Either a "route_name" or a "method" operation attribute must exist for the operation "%s" of the resource "%s".', $operationName, $resourceClass));
        }
        $route = $this->getRoute($routeName);
        $methods = $route->getMethods();
        if (empty($methods)) {
            return 'GET';
        }
        return $methods[0];
    }