The DataSet is now ready to use just as if you had created it procedurally. You can create new rows in each of its tables, using the DataTable.NewRow( ) and DataTable.Rows.Add( ) methods, as shown in Example 11-5.

using System;
using System.Data;

public class CreateData {
  public static void Main(string [ ] args) {

    DataSet dataSet = new DataSet( );
    dataSet.ReadXmlSchema("Coupons.xsd");
    
    DataTable couponsTable = dataSet.Tables["coupons"];

    DataRow couponRow = couponsTable.NewRow( );
    couponRow["coupon_code"] = "763FF";
    couponRow["discount_amount"] = 0.5;
    couponRow["discount_type"] = DiscountType.Fixed;
    couponRow["expiration_date"] = new DateTime(2002,12,31);
    couponsTable.Rows.Add(couponRow);

    dataSet.WriteXml("Coupons.xml");
  }
}

Some important highlights of this program are listed below. First, a new DataSet instance is created, and its structure is populated with the saved Coupons.xsd schema:

DataSet dataSet = new DataSet( );
dataSet.ReadXmlSchema("Coupons.xsd");

Next, the “coupons” table is retrieved using the DataTableCollection’s string indexer:

DataTable couponsTable = dataSet.Tables["coupons"];

You can only create a new row using the DataTable’s NewRow( ) factory method. This is because the columns must be populated according to the database schema stored in the DataTable. Note that the NewRow( ) method does not actually add the new DataRow to the DataTable; that happens later:

DataRow couponRow = couponsTable.NewRow( );

Now you can access each column from the new DataRow and set its value:

couponRow["coupon_code"] = "763FF";
couponRow["discount_amount"] = 0.5;
couponRow["discount_type"] = DiscountType.Fixed;
couponRow["expiration_date"] = new DateTime(2002,12,31);

Now that the DataRow is fully populated with data, it’s time to add it to the DataTable’s DataRowCollection. If some constraint or relation was not satisfied at this point, a specific DataException is thrown, giving details as to what constraint or relation was violated:

couponsTable.Rows.Add(couponRow);

Finally, the last line writes the entire DataSet to an XML file:

dataSet.WriteXml("Coupons.xml");

The Coupons.xml file generated by the last line is shown in Example 11-6. You can see that it’s a normal XML file, and it is valid according to the schema in Coupons.xsd.

<?xml version="1.0" standalone="yes"?>
<AngusHardware>
  <coupons>
    <coupon_code>763FF</coupon_code>
    <discount_amount>0.5</discount_amount>
    <discount_type>1</discount_type>
    <expiration_date>2002-12-31T00:00:00.0000000-05:00</expiration_date>
  </coupons>
</AngusHardware>

Remember, you can always verify that any XML file is valid according to a DTD or XML Schema with the XmlValidatingReader:

XmlSchema schema  = XmlSchema.Read(
  new FileStream("Coupons.xsd", FileMode.Open), null);

XmlValidatingReader reader = new XmlValidatingReader(
  new XmlTextReader("Coupons.xml"));
reader.Schemas.Add(schema);
reader.ValidationType = ValidationType.Schema;

while (reader.Read( )) {
  // this will throw an exception if invalid
}

You can also create an XML file that contains both the schema to define the DataSet structure and the data to populate it. The DataSet.WriteXml( ) method takes an additional optional parameter, an XmlWriteMode enumeration instance. The following list shows its values and what effect they have:

Reading a DataSet’s structure and contents is done in a similar fashion. The DataSet.ReadXml( ) method takes an optional XmlReadMode enumeration parameter. The following lists its possible values and their effects: