private static async Task <UserDefinedFunction> CreateUserDefinedFunction(IDocumentClient client, string udfId)
        {
            string userDefinedFunctionFileName = $@"..\..\Server\{udfId}.js";
            string udfBody = File.ReadAllText(userDefinedFunctionFileName);
            UserDefinedFunction udfDefinition = new UserDefinedFunction
            {
                Id   = udfId,
                Body = udfBody
            };

            ResourceResponse <UserDefinedFunction> result = await client.CreateUserDefinedFunctionAsync(MyStoreCollectionUri, udfDefinition);

            UserDefinedFunction udf = result.Resource;

            Console.WriteLine($" Created user defined function {udf.Id}; RID: {udf.ResourceId}");

            return(udf);
        }