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Using Annotations with a Typed DataSet

Annotations enable you to modify the names of the elements in your typed DataSet without modifying the underlying schema. Modifying the names of the elements in your underlying schema would cause the typed DataSet to refer to objects that do not exist in the data source, as well as losing a reference to the objects that do exist in the data source.

Using annotations, you can customize the names of objects in your typed DataSet with more meaningful names, making code more readable and your typed DataSet easier for clients to use, while leaving underlying schema intact. For example, the following schema element for the Customers table of the Northwind database would result in a DataRow object name of CustomersRow and a DataRowCollection named Customers.

<xs:element name="Customers">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="CustomerID" type="xs:string" minOccurs="0" />
    </xs:sequence>
  </xs:complexType>
</xs:element>

A DataRowCollection name of Customers is meaningful in client code, but a DataRow name of CustomersRow is misleading because it is a single object. Also, in common scenarios, the object would be referred to without the Row identifier and instead would be simply referred to as a Customer object. The solution is to annotate the schema and identify new names for the DataRow and DataRowCollection objects. Following is the annotated version of the previous schema.

<xs:element name="Customers"codegen:typedName="Customer" codegen:typedPlural="Customers">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="CustomerID" type="xs:string" minOccurs="0" />
    </xs:sequence>
  </xs:complexType>
</xs:element>

Specifying a typedName value of Customer will result in a DataRow object name of Customer. Specifying a typedPlural value of Customers preserves the DataRowCollection name of Customers.

The following table shows the annotations available for use.

Annotation Description
typedName Name of the object.
typedPlural Name of a collection of objects.
typedParent Name of the object when referred to in a parent relationship.
typedChildren Name of the method to return objects from a child relationship.
nullValue Value if the underlying value is DBNull. See the following table for nullValue annotations. The default is _throw.

The following table shows the values that can be specified for the nullValue annotation.

nullValue Description
Replacement Value Specifies a value to be returned. The returned value must match the type of the element. For example, use nullValue="0" to return 0 for null integer fields.
_throw Throw an exception. This is the default.
_null Return a null reference or throw an exception if a primitive type is encountered.
_empty For strings, return String.Empty, otherwise return an object created from an empty constructor. If a primitive type is encountered, throw an exception.

The following table shows default values for objects in a typed DataSet and the available annotations.

Object/Method/Event Default Annotation
DataTable TableNameDataTable typedPlural
DataTable Methods NewTableNameRow

AddTableNameRow

DeleteTableNameRow

typedName
DataRowCollection TableName typedPlural
DataRow TableNameRow typedName
DataColumn DataTable.ColumnNameColumn

DataRow.ColumnName

typedName
Property PropertyName typedName
Child Accessor GetChildTableNameRows typedChildren
Parent Accessor TableNameRow typedParent
DataSet Events TableNameRowChangeEvent

TableNameRowChangeEventHandler

typedName

To use typed DataSet annotations, you must include the following xmlns reference in your XML Schema definition language (XSD) schema.

xmlns:codegen="urn:schemas-microsoft-com:xml-msprop"

The following is a sample, annotated schema that exposes the Customers table of the Northwind database with a relation to the Orders table included.

<?xml version="1.0" encoding="utf-8"?>
<xs:schema id="CustomerDataSet" 
      xmlns:codegen="urn:schemas-microsoft-com:xml-msprop"
      xmlns="" 
      xmlns:xs="http://www.w3.org/2001/XMLSchema" 
      xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
  <xs:element name="CustomerDataSet" msdata:IsDataSet="true">
    <xs:complexType>
      <xs:choice maxOccurs="unbounded">
        <xs:element name="Customers"codegen:typedName="Customer" codegen:typedPlural="Customers">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="CustomerID" codegen:typedName="CustomerID"type="xs:string" minOccurs="0" />
              <xs:element name="CompanyName" codegen:typedName="CompanyName"type="xs:string" minOccurs="0" />
              <xs:element name="Phone" codegen:typedName="Phone" codegen:nullValue=""type="xs:string" minOccurs="0" />
            </xs:sequence>
          </xs:complexType>
        </xs:element>
        <xs:element name="Orders"codegen:typedName="Order" codegen:typedPlural="Orders">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="OrderID" codegen:typedName="OrderID"type="xs:int" minOccurs="0" />
              <xs:element name="CustomerID" codegen:typedName="CustomerID" codegen:nullValue=""type="xs:string" minOccurs="0" />
              <xs:element name="EmployeeID" codegen:typedName="EmployeeID" codegen:nullValue="0"type="xs:int" minOccurs="0" />
              <xs:element name="OrderDate" codegen:typedName="OrderDate" codegen:nullValue="1980-01-01T00:00:00"type="xs:dateTime" minOccurs="0" />
            </xs:sequence>
          </xs:complexType>
        </xs:element>
      </xs:choice>
    </xs:complexType>
    <xs:unique name="Constraint1">
      <xs:selector xpath=".//Customers" />
      <xs:field xpath="CustomerID" />
    </xs:unique>
    <xs:keyref name="CustOrders" refer="Constraint1" codegen:typedParent="Customer" codegen:typedChildren="GetOrders">
      <xs:selector xpath=".//Orders" />
      <xs:field xpath="CustomerID" />
    </xs:keyref>
  </xs:element>
</xs:schema>

The following code example uses a strongly typed DataSet created from the sample schema. It uses one DataAdapter to populate the Customers table and another DataAdapter to populate the Orders table. The strongly typed DataSet defines the DataRelations.

Dim nwindConn As SqlConnection = New SqlConnection("Data Source=localhost;Integrated Security=SSPI;" & _
                                                   "Initial Catalog=northwind")
Dim custDA As SqlDataAdapter = New SqlDataAdapter("SELECT CustomerID, CompanyName, Phone FROM Customers", &
                                                  nwindConn)
Dim orderDA As SqlDataAdapter = New SqlDataAdapter("SELECT OrderID, CustomerID, EmployeeID, OrderDate FROM Orders", &
                                                   nwindConn)

' Populate a strongly typed DataSet.
nwindConn.Open()
Dim custDS As CustomerDataSet = New CustomerDataSet()
custDA.Fill(custDS, "Customers")
orderDA.Fill(custDS, "Orders")
nwindConn.Close()

' Add a strongly typed event.
AddHandler custDS.Customers.CustomerChanged, &
           New CustomerDataSet.CustomerChangeEventHandler(AddressOf OnCustomerChanged)

' Add a strongly typed DataRow.
Dim newCust As CustomerDataSet.Customer = custDS.Customers.NewCustomer()
newCust.CustomerID = "NEW01"
newCust.CompanyName = "My New Company"
custDS.Customers.AddCustomer(newCust)

' Navigate the child relation.
Dim customer As CustomerDataSet.Customer
Dim order As CustomerDataSet.Order

For Each customer In custDS.Customers
  Console.WriteLine(customer.CustomerID)
  For Each order In customer.GetOrders()
    Console.WriteLine(vbTab & order.OrderID)
  Next
Next

Private Shared Sub OnCustomerChanged(sender As Object, e As CustomerDataSet.CustomerChangeEvent)

End Sub
[C#]SqlConnection nwindConn = new SqlConnection("Data Source=localhost;Integrated Security=SSPI;Initial Catalog=northwind");
SqlDataAdapter custDA = new SqlDataAdapter("SELECT CustomerID, CompanyName, Phone FROM Customers", nwindConn);
SqlDataAdapter orderDA = new SqlDataAdapter("SELECT OrderID, CustomerID, EmployeeID, OrderDate FROM Orders", nwindConn);

// Populate a strongly typed DataSet.
nwindConn.Open();
CustomerDataSet custDS = new CustomerDataSet();
custDA.Fill(custDS, "Customers");
orderDA.Fill(custDS, "Orders");
nwindConn.Close();

// Add a strongly typed event.
custDS.Customers.CustomerChanged += new 
  CustomerDataSet.CustomerChangeEventHandler(OnCustomerChanged);

// Add a strongly typed DataRow.
CustomerDataSet.Customer newCust = custDS.Customers.NewCustomer();
newCust.CustomerID = "NEW01";
newCust.CompanyName = "My New Company";
custDS.Customers.AddCustomer(newCust);

// Navigate the child relation.
foreach(CustomerDataSet.Customer customer in custDS.Customers)
{
  Console.WriteLine(customer.CustomerID);
  foreach(CustomerDataSet.Order order in customer.GetOrders())
    Console.WriteLine("\t" + order.OrderID);
}

protected static void OnCustomerChanged(object sender, CustomerDataSet.CustomerChangeEvent e)
{

}

See Also

Working with a Typed DataSet | Creating and Using DataSets | DataColumnCollection Class | DataSet Class

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