Check existing record in 3 tier architecture

Front-end / web page

if (isnew_record) {
            var _bll = new businesslogiclayer();
            if (_bll.CheckExistingRecord(txtReferenceNo.Text.ToString().Trim()) > 0) {
                lblError.Text = "Reference Number already exists.";
                return;
            }
        }

Business Logic Layer

 public int CheckExistingRecord(string refnumber) {
            var _dal = new dataacceslayer();
            return _dal.CheckExistingRecord(refnumber);
        }

Data Access Layer

internal int CheckExistingRecord(string refnumber) {
            base.com.CommandText = "select count(refnumber) from tablename where refnumber = @refnumber";
            base.com.Parameters.AddWithValue("@refnumber", refnumber);
            
            return Convert.ToInt32(base.com.ExecuteScalar());

        }