The most obvious way to create a DataSet is to construct each of its objects and add them to the appropriate collections. First, create a new instance of DataSet named “AngusHardware.” The DataSet represents the entire database schema:

DataSet dataSet = new DataSet("AngusHardware");

Next, add a table named “customers” to the DataSet. The DataTableCollection.Add( ) method has several overloads; by passing a string parameter, you’re creating a new DataTable with the given name, and adding it to the DataSet’s Tables property. Add( ) returns the newly created DataTable, which you’ll use to create columns:

DataTable customers = dataSet.Tables.Add("customers");

Next, add a column to the “customers” table. The DataColumnCollection.Add( ) method returns the newly created DataColumn, which you’ll use in a minute to assign the primary key. This Add( ) method, like the one on DataTableCollection, has several overloads. The one used here simply takes the name of the database column and the Type of the data it contains:

DataColumn customersCustomerId = customers.Columns.Add("customer_id",
   typeof(long));

The process is similar for each column. Note that some columns are nullable in the database and others are not; the AllowDBNull property indicates whether the column is nullable:

customers.Columns.Add("name",typeof(string)).AllowDBNull = false;
customers.Columns.Add("address1",typeof(string)).AllowDBNull = false;
customers.Columns.Add("address2",typeof(string));
customers.Columns.Add("address3",typeof(string));
customers.Columns.Add("city",typeof(string)).AllowDBNull = false;
customers.Columns.Add("state",typeof(string)).AllowDBNull = false;
customers.Columns.Add("zip",typeof(string)).AllowDBNull = false;

The last step for the “customers” table is to set the primary key, using the customersCustomerId DataColumn created a minute ago. Although this table has a simple, one-column primary key, the DataSet allows for concatenated primary keys via an array of DataColumn objects:

customers.PrimaryKey = new DataColumn [ ] {customersCustomerId};

A very similar process creates the “coupons” table:

DataTable coupons = dataSet.Tables.Add("coupons");
DataColumn couponCouponCode = coupons.Columns.Add("coupon_code",   
  typeof(string));
coupons.Columns.Add("discount_amount", 
  typeof(Double)).AllowDBNull = false;
coupons.Columns.Add("discount_type", typeof(int)).AllowDBNull = false;
coupons.Columns.Add("expiration_date", 
  typeof(DateTime)).AllowDBNull = false;
coupons.PrimaryKey = new DataColumn [ ] {couponCouponCode};

And again for the “coupon_redemptions” table:

DataTable couponRedemptions = 
  dataSet.Tables.Add("coupon_redemptions");
DataColumn couponRedemptionsCouponCode = 
  couponRedemptions.Columns.Add("coupon_code", typeof(string));
couponRedemptions.Columns.Add("total_discount", typeof(Double)).AllowDBNull = false;
couponRedemptions.Columns.Add("redemption_date", typeof(DateTime)).AllowDBNull = false;
DataColumn couponRedemptionsCustomerId = 
  couponRedemptions.Columns.Add("customer_id", typeof(long));

Now that all the tables are created, it’s time to assign the relations between them. The DataSet has a DataRelationCollection, whose Add( ) method has several overloads. The one used here takes the parent DataColumn and the child DataColumn. There are two relations in this example; one between coupons.coupon_code and coupon_redemptions.coupon_code, and one between customers.customer_id and coupon_redemptions.customer_id:

dataSet.Relations.Add(couponCouponCode, couponRedemptionsCouponCode);
dataSet.Relations.Add(customersCustomerId, 
  couponRedemptionsCustomerId);

Finally, this line writes an XML Schema document that describes the DataSet to a file:

dataSet.WriteXmlSchema("Coupons.xsd");

The XML Schema that this program saved in Coupons.xsd is a normal XML Schema, and it can be used to recreate the DataSet in memory. The code to read in a DataSet’s structure from a schema is very simple. In fact, it can be expressed succinctly in two statements:

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

Example 11-4 shows the complete program that creates the DataSet for the coupon database, and saves an XML Schema for it.

using System;
using System.Data;

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

    DataSet dataSet = new DataSet("AngusHardware");

    DataTable customers = dataSet.Tables.Add("customers");
    DataColumn customersCustomerId = customers.Columns.Add("customer_id",
      typeof(long));
    customers.Columns.Add("name",typeof(string)).AllowDBNull = false;
    customers.Columns.Add("address1",typeof(string)).AllowDBNull = false;
    customers.Columns.Add("address2",typeof(string));
    customers.Columns.Add("address3",typeof(string));
    customers.Columns.Add("city",typeof(string)).AllowDBNull = false;
    customers.Columns.Add("state",typeof(string)).AllowDBNull = false;
    customers.Columns.Add("zip",typeof(string)).AllowDBNull = false;
    customers.PrimaryKey = new DataColumn [ ] {customersCustomerId};

    DataTable coupons = dataSet.Tables.Add("coupons");
    DataColumn couponCouponCode = coupons.Columns.Add("coupon_code",   
      typeof(string));
    coupons.Columns.Add("discount_amount", 
      typeof(Double)).AllowDBNull = false;
    coupons.Columns.Add("discount_type", typeof(int)).AllowDBNull = false;
    coupons.Columns.Add("expiration_date", 
      typeof(DateTime)).AllowDBNull = false;
    coupons.PrimaryKey = new DataColumn [ ] {couponCouponCode};

    DataTable couponRedemptions = 
      dataSet.Tables.Add("coupon_redemptions");
    DataColumn couponRedemptionsCouponCode = 
      couponRedemptions.Columns.Add("coupon_code", typeof(string));
    couponRedemptions.Columns.Add("total_discount",
      typeof(Double)).AllowDBNull = false;
    couponRedemptions.Columns.Add("redemption_date", 
      typeof(DateTime)).AllowDBNull = false;
    DataColumn couponRedemptionsCustomerId = 
      couponRedemptions.Columns.Add("customer_id", typeof(long));

    dataSet.Relations.Add(couponCouponCode, couponRedemptionsCouponCode);
    dataSet.Relations.Add(customersCustomerId, 
      couponRedemptionsCustomerId);

    dataSet.WriteXmlSchema("Coupons.xsd");
  }
}