把DATASET转成XML（主从表结构）

    Dim objConn As OracleConnection
        Dim objDataAdapter As OracleDataAdapter
        Dim strConn As String = "user id=scott;password=tiger;data source=orcl"
        Dim strSql As String
        Dim ds As DataSet
        Dim objXmlDataDoc As XmlDataDocument
        Try
            objConn = New OracleConnection(strConn)
            ds = New DataSet("DeptEmp")

            strSql = "select * from emp"
            objDataAdapter = New OracleDataAdapter(strSql, objConn)
            objDataAdapter.Fill(ds, "Employee")

            strSql = "select * from dept"
            objDataAdapter.SelectCommand.CommandText = strSql
            objDataAdapter.Fill(ds, "Dept")

            ds.CaseSensitive = False
            ds.Relations.Add("DeptEmployees", _
                           ds.Tables("Dept").Columns("DeptNo"), _
                           ds.Tables("Employee").Columns("DeptNo")).Nested = True

            ds.WriteXml("DeptEmployees.xml")

        Catch ex As Exception
            Console.WriteLine(ex.Message)
            Console.ReadLine()
        End Try

保存以后的XML的格式
<?xml version="1.0"?>
<testds>
  <dt1 name="dt1">
    <id>a</id>
    <dt1c2>111</dt1c2>
    <dt2 name="dt2">
       <dt2c1>d2</dt2c1>
       <dt2c2>adad</dt2c2>
    </dt2>
  </dt1>
  
</testds>