比较两个DataSet，并由此产生新的DataSet

 /// <summary>
        /// 比较两个DataSet，并产生增量数据
        /// </summary>
        /// <param name="oldDataSet">原始DataSet</param>
        /// <param name="nowDataSet">现有DataSet</param>
        /// <param name="primaryKey">原始DataSet和现有DataSet Tables[0]的主键</param>
        /// <returns>DataSet</returns>
        public DataSet CompareDataSet(DataSet oldDataSet,DataSet nowDataSet,string primaryKey)
        {
            //更新nowDataSet中的所有行，使之状态为DataRowState.UnChanged
            nowDataSet.AcceptChanges();
            //要返回的DataSet
            DataSet newDataSet = new DataSet();

            //设置oldDataSet 和 newDataSet Tables[0] 的主键
            DataColumn dcOld = oldDataSet.Tables[0].Columns[primaryKey];            
            DataColumn dcNow = nowDataSet.Tables[0].Columns[primaryKey];
            //设置主键
            oldDataSet.Tables[0].PrimaryKey = new DataColumn[1] { dcOld };
            nowDataSet.Tables[0].PrimaryKey = new DataColumn[1] { dcNow };

            string primaryValue = string.Empty;
            string where = string.Empty;

            foreach (DataRow drNow in nowDataSet.Tables[0].Rows)
            {
                //每行数据中，主键列所对应的值
                primaryValue = drNow[primaryKey].ToString();
                where = primaryKey + " = '" + primaryValue + "'";

                //在oldDataSet 中查找和主键相同的行
                DataRow[] drOld = oldDataSet.Tables[0].Select(where);
                if (drOld.Length == 0)
                {
                    drNow.SetModified();
                }//说明nowDataSet中的这行数据是新增加的数据
                else
                {
                    for (int i = 0; i < drNow.ItemArray.Length; i++)
                    {
                        if (drNow.ItemArray.GetValue(i).ToString().Equals(drOld[0].ItemArray.GetValue(i).ToString()) == false)
                        {
                            drNow.SetModified();
                            break;
                        }//说明nowDataSet中的这行数据是修改过的数据
                    }
                }//判断两行中的每一列是否相等
            }

            //装载DataRowState为 Modified的行
            newDataSet.Tables.Add(nowDataSet.Tables[0].GetChanges(DataRowState.Modified));

            return newDataSet;
        }