class PgConn::RoleMethods

def list(database: nil, owner: false, superuser: nil, can_login: nil)
  database_clause = database && "rolname like '#{database}\\_\\_%'"
  database_clause = database && "(#{database_clause} or rolname = '#{database}')" if owner
  superuser_clause = superuser.nil? ? nil : "rolsuper = #{superuser}"
  can_login_clause = can_login.nil? ? nil : "rolcanlogin = #{can_login}"
  query = [
      "select rolname from pg_roles where true",
      database_clause, superuser_clause, can_login_clause
  ].compact.join(" and ")
  conn.values(query)
end