code: func NamedQueryContext(ctx context.Context, e ExtContext, query string, arg interface{}) (*Rows, error) {
  	q, args, err := bindNamedMapper(BindType(e.DriverName()), query, arg, mapperFor(e))
  	if err != nil {
  		return nil, err
  	}
  	return e.QueryxContext(ctx, q, args...)
  }
docs: // NamedQueryContext binds a named query and then runs Query on the result using the
  // provided Ext (sqlx.Tx, sqlx.Db).  It works with both structs and with
  // map[string]interface{} types.