How to: Control the Type of a Projection
Projection is the process of taking one set of data, filtering it, changing its shape, and even changing its type. Most query expressions perform projections. Most of the query expressions shown in this section evaluate to IEnumerable<T> of XElement, but you can control the type of the projection to create collections of other types. This topic shows how to do this.
Example
The following example defines a new type, Customer. The query expression then instantiates new Customer objects in the Select clause. This causes the type of the query expression to be IEnumerable<T> of Customer.
This example uses the following XML document: Sample XML File: Customers and Orders (LINQ to XML).
public class Customer
{
private string customerID;
public string CustomerID{ get{return customerID;} set{customerID = value;}}
private string companyName;
public string CompanyName{ get{return companyName;} set{companyName = value;}}
private string contactName;
public string ContactName { get{return contactName;} set{contactName = value;}}
public Customer(string customerID, string companyName, string contactName)
{
CustomerID = customerID;
CompanyName = companyName;
ContactName = contactName;
}
public override string ToString()
{
return String.Format("{0}:{1}:{2}", this.customerID, this.companyName, this.contactName);
}
}
class Program
{
static void Main(string[] args)
{
XElement custOrd = XElement.Load("CustomersOrders.xml");
IEnumerable<Customer> custList =
from el in custOrd.Element("Customers").Elements("Customer")
select new Customer(
(string)el.Attribute("CustomerID"),
(string)el.Element("CompanyName"),
(string)el.Element("ContactName")
);
foreach (Customer cust in custList)
Console.WriteLine(cust);
}
}
Public Class Customer
Private customerIDValue As String
Public Property CustomerID() As String
Get
Return customerIDValue
End Get
Set(ByVal value As String)
customerIDValue = value
End Set
End Property
Private companyNameValue As String
Public Property CompanyName() As String
Get
Return companyNameValue
End Get
Set(ByVal value As String)
companyNameValue = value
End Set
End Property
Private contactNameValue As String
Public Property ContactName() As String
Get
Return contactNameValue
End Get
Set(ByVal value As String)
contactNameValue = value
End Set
End Property
Public Sub New(ByVal customerID As String, _
ByVal companyName As String, _
ByVal contactName As String)
CustomerIDValue = customerID
CompanyNameValue = companyName
ContactNameValue = contactName
End Sub
Public Overrides Function ToString() As String
Return String.Format("{0}:{1}:{2}", Me.CustomerID, Me.CompanyName, Me.ContactName)
End Function
End Class
Sub Main()
Dim custOrd As XElement = XElement.Load("CustomersOrders.xml")
Dim custList As IEnumerable(Of Customer) = _
From el In custOrd.<Customers>.<Customer> _
Select New Customer( _
el.@<CustomerID>, _
el.<CompanyName>.Value, _
el.<ContactName>.Value _
)
For Each cust In custList
Console.WriteLine(cust)
Next
End Sub
This code produces the following output:
GREAL:Great Lakes Food Market:Howard Snyder
HUNGC:Hungry Coyote Import Store:Yoshi Latimer
LAZYK:Lazy K Kountry Store:John Steel
LETSS:Let's Stop N Shop:Jaime Yorres