XML files with LINQ

1
XML files (with LINQ)
2
Introduction to LINQ (Language Integrated
Query )

• Cs new LINQ capabilities allow you to write
  query expressions that retrieve information from
  many data sources, not just databases.
• foreach (var number in myArray)
• The implicitly typed local-variable feature is
  one of several new C features that support LINQ.
  
• LINQ to Objects can be used to filter arrays and
  Lists, selecting elements that satisfy a set of
  conditions
• Repetition statements that filter arrays focus on
  the steps required to get the results. This is
  called imperative programming.
• LINQ queries, however, specify the conditions
  that selected elements must satisfy. This is
  known as declarative programming.
• The System.Linq namespace contains the LINQ to
  Objects provider.

3
Using LINQ with arrays

• Lets look at an example LINQWithSimpleTypeArray
• // values greater than 4
• var filtered from value in values
• where value gt 4
• select value
• var sorted from value in values
• orderby value
• select value
• var sorted from value in filtered
• orderby value descending
• select value

A LINQ query begins with a from clause, which
specifies a range variable (value) and the data
source to query (values).
If the condition in the where clause evaluates to
true, the element is selected.
The select clause determines what value appears
in the results.
The orderby clause sorts the query results in
ascending order.
The descending modifier in the orderby clause
sorts the results in descending order.
4
Using LINQ with arrays of objects

• Employee class (Employee.cs)
• LINQWithArrayOfObjects.cs
• Lets fill the empty one ourselves together
• var nameSorted
• from e in employees
• orderby e.LastName, e.FirstName
• select e
• if (nameSorted.Any())
• Console.WriteLine(nameSorted.First().ToString()
  "\n")
• else
• Console.WriteLine("not found\n")

An orderby clause can sort the results according
to multiple properties, specified in a
comma-separated list.
The query results Any method returns true if
there is at least one element, and false if there
are no elements.
The query results First method (line 45) returns
the first element in the result
5
Using LINQ with arrays of objects

• Display( lastNames.Distinct(),
• "Unique employee last names")
• // use LINQ to select first and last names
• var names
• from e in employees
• select new e.FirstName, Last
  e.LastName

The Distinct method removes duplicate elements,
causing all elements in the result to be unique.
The select clause can create a new object of
anonymous type (a type with no name), which the
compiler generates for you based on the
properties listed in the curly braces ().
6
Using LINQ with ListltTgt

• ListltTgt is a generic list and its members are as
  follows

7
Using LINQ with Lists

• LINQWithListCollection.cs
• var startsWithR
• from item in items
• let uppercaseString
  item.ToUpper()
• where uppercaseString.StartsWith
  ("R")
• orderby uppercaseString
• select uppercaseString
• LINQs let clause can be used to create a new
  range variable to store a temporary result for
  use later in the LINQ query.

8
Introduction

• The .NET Framework uses XML extensively.
• Configuration files use XML format.
• http//msdn.microsoft.com/en-us/library/1xtk877y(V
  S.71).aspx
• XML is also used heavily in serialization.
• LINQ to XML provides a way to manipulate data in
  XML documents using the same LINQ syntax you can
  use on arrays, collections, and databases.
• LINQ to XML also provides a set of classes for
  easily navigating and creating XML documents in
  your code.

9
XML files

• On successfully parsing a document, some XML
  parsers store document data as trees in memory.
• Figure below illustrates the tree structure for
  the document article.xml.

10
XML files DOM

• This hierarchical tree structure is called a
  Document Object Model (DOM) tree, and an XML
  parser that creates such a tree is known as a DOM
  parser.
• Each element name is represented by a node.
• A node that contains other nodes (called child
  nodes or children) is called a parent node.
• A parent node can have many children, but a child
  node can have only one parent node.
• Nodes that have the same parent are called
  sibling nodes.
• A nodes descendant nodes include its children,
  its childrens children and so on.
• A nodes ancestor nodes include its parent, its
  parents parent and so on.
• The DOM tree has a single root node, which
  contains all the other nodes in the document.
• Classes for creating, reading and manipulating
  XML documents are located in the System.Xml
  namespace.

11
Reading XML files

• Namespace System.Xml.Linq contains the classes
  used to manipulate a DOM in .NET, referred to
  collectively as LINQ to XML.
• The XElement class represents a DOM element
  nodean XML document is represented by a tree of
  XElement objects.
• The XDocument class represents an entire XML
  document.
• Example XDocumentTestForm.cs to read article.xml

12
Reading XML files

• XDocuments static Load method takes an XML
  documents filename and returns an XDocument
  containing a tree representation of the XML file.
• The XDocument s Root property returns an
  XElement representing the root element of the XML
  file.
• Because full element names consist of namespace
  prefix and name parts, tag and attribute names
  are stored as objects of class XName.
• The Name property of an XElement returns an XName
  object containing the tag name and namespace
• The unqualified name is stored in the XNames
  LocalName property.
• The HasElements property can be used to test
  whether an elements has any child elements.
• The Elements method is used to obtain an
  elements children.
• An elements text can be obtained using the Value
  property.
• If used on an element with children, the Value
  property returns all of the text contained within
  its descendants, with the tags removed.

13
Writing to XML files

• You can add content (elements, attributes,
  comments, processing instructions, text) to an
  existing XML tree.
• Add child content to an XElement or an XDocument
• XDocument.Add and XDocument.AddFirst
• Add content as sibling nodes of an XNode
• XDocument.AddAfterSelf and XDocument.AddBeforeSelf
  
• Then XDocument.Save writes to the file.
• Modifying Elements, Attributes, and Nodes in an
  XML Tree
• Removing Elements, Attributes, and Nodes from an
  XML Tree

14
LINQ to XML Class Hierarchy
15
Navigate the XML document

• Example XMLFileTreeView solution

16
LINQ to XML Class Hierarchy

• The XDocuments Elements method can return all
  child elements, or only elements with a given tag
  name.
• The Elements method is actually defined in the
  XContainer class, the base class of XDocument and
  XElement.
• The Descendants method returns all descendant
  elements with the given tag name, not just direct
  children.
• The Element method, a member of the XContainer
  class, returns the first child element with the
  given tag name or null if no such element exists.
• The Attribute method of the XElement class
  returns an XAttribute object matching the given
  attribute name or null if no such object exists.
• The XAttribute class represents an XML
  attributeit holds the attributes name and
  value.

17
LINQ to XML Class Hierarchy

• XObject class is an abstract base class for all
  nodes and attributes.
• The NodeType property returns a value of the
  XmlNodeType enumeration .
• The Parent property of XObject, which returns the
  parent of the given XObject or null if the parent
  does not exist.
• The Document property (defined in XObject)
  retrieves the XDocument representing the document
  root.
• The XNode class is a common abstract base class
  of all the node types in an XML document.
• The PreviousNode of XNode returns the previous
  sibling, or null if there is none.
• NextNode returns the next sibling node in the
  tree, or null if there is none.
• The ToString methods of all subclasses of XNode
  return the XML they and their children (if any)
  represent with proper indentation.
• The Nodes method of XContainer returns a
  reference to an object of type IEnumerableltXNodegt
  containing all children of the given XContainer.
• XText holds the contents of a text node. Its
  Value property returns the contained text.
• Comments are represented by the XComment class.

18
More to learn

• http//msdn.microsoft.com/en-us/library/bb387098.a
  spx