Introduction to LINQ To XML

Monthly Features: Technical Showcase
What is LINQ to XML?
Microsoft says:
“LINQ to XML provides an in-memory XML programming interface that leverages the .NET Language-Integrated Query (LINQ) Framework. LINQ to XML uses the latest .NET Framework language capabilities and is comparable to an updated, redesigned Document Object Model (DOM) XML programming interface.”

What is LINQ to XML?
Alternative to using XPath
Uses anonymous types to provide strongly typed access to XML elements and attributes.
Not a replacement for XSLT

Sample XML File
<?xmlversion="1.0"encoding="utf-8" ?>
<PurchaseOrders>
<PurchaseOrderId="83123"Total="59.97">
<CustomerName>Joe Bob</CustomerName>
<CustomerState>TX</CustomerState>
<Items>
<ItemId="26134"Name="Polo Shirt"Color="Blue"Price="19.99" />
<ItemId="32324"Name="T-Shirt"Color="White"Price="9.99" />
<ItemId="01283"Name="Jeans"Color="Blue"Price="29.99" />
</Items>
</PurchaseOrder>
<CustomerName>Bob Joe</CustomerName>
<Items>
<ItemId="26134"Name="Polo Shirt"Color="Red"Price="19.99" />
</Items>
</PurchaseOrder>
<CustomerName>John Smith</CustomerName>
<CustomerState>OK</CustomerState>
<Items>
</Items>
</PurchaseOrder>
</PurchaseOrders>

Get PurchaseIds of orders greater than $40.00
Returns
XDocumentpurchaseOrderXml = XDocument.Load("PurchaseOrder.xml");

varpurchaseIds = frompurchaseOrderinpurchaseOrderXml.Root.Elements("PurchaseOrder")
wherefloat.Parse(purchaseOrder.Attribute("Total").Value) > 40.00f
selectpurchaseOrder.Attribute("Id").Value;

foreach (varpurchaseIdinpurchaseIds)
Console.WriteLine("PurchaseId: {0}", purchaseId);
Order Ids Greater than $40.00
PurchaseId: 83123
PurchaseId: 83125

Add a reference to System.Xml.Linq.
Classes
XDocument– Class used to interact with an XML document
XElement– Represents an element in an XML document
XAttribute– Represents an attribute in an XML document
XNamespace – Used to specify a namespace in an XML document
i.e.: /my:myFields/my:RepeatingTable
LINQ to XML Classes

Methods and Properties
XDocument.Root– Returns the root XElement of the XML document
XContainer.Elements() – Returns an IEnumberable<XElement> of all matching elements
Example: myDocument.Root.Elements(“PurchaseOrders”);
XContainer.Attributes() – Returns an IEnumerable<XAttribute>
XContainer.Element() – Returns a single XElement
Example: purchaseOrderElement.Element(“CustomerName”).Value;
XContainer.Attribute() – Returns a single XAttribute
.Any() Extension Method – Returns true if items exist in a IEnumerable<>
.First() Extension Method – Returns first item in an IEnumberable<>
LINQ to XML Methods and Properties

Sample XML File
<PurchaseOrders>
<Items>
</Items>
</PurchaseOrder>
<Items>
</Items>
</PurchaseOrder>
<Items>
</Items>
</PurchaseOrder>
</PurchaseOrders>

Get Purchase Orders greater than $40.00
Returns

varpurchaseOrders = frompurchaseOrderinpurchaseOrderXml.Root.Elements("PurchaseOrder")
wherefloat.Parse(purchaseOrder.Attribute("Total").Value) > 40.00f
selectnew
{
Id = purchaseOrder.Attribute("Id").Value,
Total = float.Parse(purchaseOrder.Attribute("Total").Value),
CustomerName = purchaseOrder.Element("CustomerName").Value,
CustomerState = purchaseOrder.Element("CustomerState").Value
};

foreach (varpurchaseOrderinpurchaseOrders)
Console.WriteLine("PurchaseId: {0}: {1} ({2}) - {3}",
purchaseOrder.Id,
purchaseOrder.CustomerName,
purchaseOrder.CustomerState,
purchaseOrder.Total);
Returns
Orders Greater than $40.00
PurchaseId: 83123: Joe Bob (TX) - 59.97
PurchaseId: 83125: John Smith (OK) - 49.98

Sample XML File
<PurchaseOrders>
<Items>
</Items>
</PurchaseOrder>
<Items>
</Items>
</PurchaseOrder>
<Items>
</Items>
</PurchaseOrder>
</PurchaseOrders>

Get Purchase Orders with at least 2 items
Returns

varpurchaseOrders = frompurchaseOrderinpurchaseOrderXml.Root.Elements("PurchaseOrder")
wherepurchaseOrder.Element("Items").Elements("Item").Count() >= 2
selectnew
{
Id = purchaseOrder.Attribute("Id").Value,
ItemCount = purchaseOrder.Element("Items").Elements("Item").Count()
};

foreach (varpurchaseOrderinpurchaseOrders)
Console.WriteLine("PurchaseId: {0}: ItemCount: {1}",
purchaseOrder.Id,
purchaseOrder.ItemCount);
Returns
Orders With at least 2 items
PurchaseId: 83123: ItemCount: 3
PurchaseId: 83125: ItemCount: 2

InfoPath
<my:myFieldsxmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2008-12-30T15:48:37"
xmlns:xd="http://schemas.microsoft.com/office/infopath/2003"xml:lang="en-US">
<my:RepeatingTable>
<my:Item>
<my:Name>Polo Shirt</my:Name>
<my:Color>Red</my:Color>
<my:Price>19.99</my:Price>
</my:Item>
<my:Item>
<my:Name>Jeans</my:Name>
<my:Color>Blue</my:Color>
<my:Price>29.99</my:Price>
</my:Item>
</my:RepeatingTable>
<my:Id>83123</my:Id>
</my:myFields>

Querying a repeating table in InfoPath
Reference System.Linq (contained in System.Core)
Reference System.Xml.Linq (contained in System.Xml.Linq)
Returns
// use the MainDataSource to read the XML of the InfoPath Form
XDocumentinfoPathDocument = XDocument.Load(newSystem.IO.StringReader(MainDataSource.CreateNavigator().OuterXml));

// required to access my: namespace
XNamespacemyNamespace = "http://schemas.microsoft.com/office/infopath/2003/myXSD/2008-12-30T15:48:37";

// use descendants node to find any element with the name Item in the tree
var items = from item ininfoPathDocument.Descendants(myNamespace + "Item")
selectnew
{
Name = item.Element(myNamespace + "Name").Value,
Color = item.Element(myNamespace + “Color").Value,
Price = item.Element(myNamespace + "Price").Value
};

foreach (var item in items)
{
// do something
}

Questions?
Code Samples available at www.dotnetmafia.com.

Introduction to LINQ To XML

by Corey Roth

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