I found issue with db driver

I am using pdo driver and my query is

PHP Code:

$query = $this->db->select()->from('community_list')->where('community_name',$community);
        $rows = $query->num_rows(); 


Its show me error like

Code:

Severity: Notice

Message: Array to string conversion

Filename: database/DB_query_builder.php

Line Number: 662