比较两个DataSet，并产生增量数据

/// <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;
    }