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How to write queries with complex filtering (LINQ to XML)

Sometimes you want to write LINQ to XML queries with complex filters. For example, you might have to find all elements that have a child element with a particular name and value. This article gives an example of writing a query with complex filtering.

Example: Find with a nested query in the Where clause

This example shows how to find all PurchaseOrder elements that have:

  • A child Address element whose Type attribute equals "Shipping".
  • A child State element that equals "NY".

It uses a nested query in the Where clause, and the Any operator returns true if the collection has any elements in it. The example uses XML document Sample XML file: Multiple purchase orders.

For more information about the Any operator, see Quantifier Operations (C#) and Quantifier Operations (Visual Basic).

XElement root = XElement.Load("PurchaseOrders.xml");
IEnumerable<XElement> purchaseOrders =
    from el in root.Elements("PurchaseOrder")
    where
        (from add in el.Elements("Address")
        where
            (string)add.Attribute("Type") == "Shipping" &&
            (string)add.Element("State") == "NY"
        select add)
        .Any()
    select el;
foreach (XElement el in purchaseOrders)
    Console.WriteLine((string)el.Attribute("PurchaseOrderNumber"));

Dim root As XElement = XElement.Load("PurchaseOrders.xml")
Dim purchaseOrders As IEnumerable(Of XElement) = _
    From el In root.<PurchaseOrder> _
    Where _
        (From add In el.<Address> _
        Where _
             add.@Type = "Shipping" And _
             add.<State>.Value = "NY" _
        Select add) _
    .Any() _
    Select el
For Each el As XElement In purchaseOrders
    Console.WriteLine(el.@PurchaseOrderNumber)
Next

This example produces the following output:

99505

Example: Find in XML that's in a namespace

The following example shows the same query as above, but for XML that's in a namespace. For more information, see Namespaces overview.

This example uses XML document Sample XML file: Multiple purchase orders in a namespace.

XElement root = XElement.Load("PurchaseOrdersInNamespace.xml");
XNamespace aw = "http://www.adventure-works.com";
IEnumerable<XElement> purchaseOrders =
    from el in root.Elements(aw + "PurchaseOrder")
    where
        (from add in el.Elements(aw + "Address")
         where
             (string)add.Attribute(aw + "Type") == "Shipping" &&
             (string)add.Element(aw + "State") == "NY"
         select add)
        .Any()
    select el;
foreach (XElement el in purchaseOrders)
    Console.WriteLine((string)el.Attribute(aw + "PurchaseOrderNumber"));

Imports <xmlns:aw='http://www.adventure-works.com'>

Module Module1
    Sub Main()
        Dim root As XElement = XElement.Load("PurchaseOrdersInNamespace.xml")
        Dim purchaseOrders As IEnumerable(Of XElement) = _
            From el In root.<aw:PurchaseOrder> _
            Where _
                (From add In el.<aw:Address> _
                Where _
                     add.@aw:Type = "Shipping" And _
                     add.<aw:State>.Value = "NY" _
                Select add) _
            .Any() _
            Select el
        For Each el As XElement In purchaseOrders
            Console.WriteLine(el.@aw:PurchaseOrderNumber)
        Next
    End Sub
End Module

This example produces the following output:

99505

See also