新增/修改时，唯一性字段检查

一个对象，比如订单Order
有一个无意义的orderId作为唯一标识属性，还有一个有意义的订单号orderNo
orderNo也必须是唯一的,在添加修改数据的时候，就存在校验唯一性的问题

先假设有表order,保含2个字段,orderid,orderNo

1.新增
  我们写一个通用的校验类,有一个check方法，参数为表名，校验的列名，列的值


  CheckUnique.java

  public class CheckUnique {
 public static boolean check(
  String tablemame,
  String coluname,
  String coluvalue)
  throws BaseException {

  boolean isExist = false;

  Connection con = null;
  Statement pstmt = null;
  ResultSet rs = null;

  try {
   con = BaseDAO.getConnection();
   String strSql = "";
   strSql =
    "select count(1) as count  from "
     + tablemame
     + " where "
     + coluname
     + "="
     + coluvalue;
     
   Debug.printErr(strSql);  

   pstmt = con.createStatement();
   rs = pstmt.executeQuery(strSql);
   int totalNum = 0;
   if (rs.next()) {
    totalNum = rs.getInt("count");

    if (totalNum != 0)
     isExist = true;
   }

  } catch (SQLException sql) {
   try {
    if (con != null)
     con.rollback();
   } catch (Exception e) {
   }
   throw new BaseException(sql.getMessage());
  } finally {
   try {
    rs.close();
   } catch (SQLException e) {
   }
   try {
    pstmt.close();
   } catch (SQLException e) {
   }
  }
  return isExist;
 }
}

  现在我们就可以通过CheckUnique.check("order","orderNo","20050501111")来校验orderNo

2.修改
修改的校验要比新增麻烦，因为修改的时候，检测orderNo当然是存在了。
在CheckUnique类添加新方法checkUpdate(String tableName,   //表名
                                                                    String idColName,  //主键列名
                                                                    String idColValue, //主键列值
                                                                    String uniColName, //校验列名
                                                                    String uniColVaue) //校验列值
方法内容基本和check()方法一样，只是sql语句strSql不同，strSql如下

 select count(1) as count  from tableName t1
 where t1.uniColName=uniColVaue
 and t1.idColName not in
 (
   select t2.idColName from tableName t2
   where t2.idColName=idColValue and t2.uniColName=uniColVaue
 )
 
 order的例子
  select count(1) as count  from order t1
 where t1.orderNo='200505001111'
 and t1.orderId not in
 (
   select t2.orderId from order t2
   where t2.orderId=9527 and t2.orderNo='200505001111'
 )