LINQ to XML Fagdag Fredag, 20.november 2009

In-memory XML programming interface Gamle-måten:  XmlDocument / DOM  XPath  XQuery Med LINQ:  XDocument / XElement  LINQ query expressions Fagdag, 20.november 2009 Side 2 Hva er LINQ to XML?

Hvorfor LINQ to XML?  “Lettere” objektmodell enn DOM  Enklere syntax  Drar nytte av språkforbedringer i C#  LINQ er integrert i (C# 2008):  Intellisens  Sterkere typing  Compile-time sjekking  Bedre debugger-støtte  Functional construction (XElement,XAttribute) Fagdag, 20.november 2009 Side 3

Lese XML inn i minnet XDocument.Load("Books.xml"); XElement.Load("Books.xml"); Fagdag, 20.november 2009 Side 4

Lese XML inn i minnet XElement.Load(” ion/rss.aspx"); Fagdag, 20.november 2009 Side 5

Lese XML inn i minnet XElement.Load(XmlReader); XElement.Load(TextReader); Fagdag, 20.november 2009 Side 6

Skrive til fil XDocument xDoc = XDocument.Load("Books.xml"); xDoc.Save("Books2.xml"); XElement xElem = XElement.Load("Books.xml"); xElem.Save("Books2.xml"); Fagdag, 20.november 2009 Side 7

Skrive til stream StringBuilder output = new StringBuilder(); XmlWriterSettings xmlWriterSettings = new XmlWriterSettings {OmitXmlDeclaration = true}; using (XmlWriter writer = XmlWriter.Create(output, xmlWriterSettings)) { XElement root = myXElement; root.Save(writer); } Fagdag, 20.november 2009 Side 8

Konstruere xml XElement xml = new XElement("contacts”, new XElement("contact”, new XAttribute("contactId", "2"), new XElement(”name", ”Homer Simpson”) ), new XElement("contact”, new XAttribute("contactId", "3"), new XElement(”name", ”Mr. Burns") ) ); xml.Save(”contacts.xml”); Fagdag, 20.november 2009 Side 9

Contacts.xml Homer Simpson Mr. Burns Fagdag, 20.november 2009 Side 10

Manipulere xml: Add xElement.Add(new XElement("NewChild", "new content") ); AddFirst, AddAfterSelf, AddBeforeSelf xElement.Add(new XAttribute("NewAttribute", "attr content”) ); Fagdag, 20.november 2009 Side 11

Manipulere xml: Set Element xElement.Parse(” value "); ReplaceAll SetElementValue Value SetValue ReplaceWith( someOtherElement ) ReplaceNodes( otherElements ) Fagdag, 20.november 2009 Side 12

Manipulere xml: Set Attribute xElement.ReplaceAttributes(new XAttribute("attrName", "value")); SetAttributeValue Value SetValue Fagdag, 20.november 2009 Side 13

Manipulere xml: Remove element xElement.Remove(); xElement.RemoveNodes(); xElement.RemoveAll(); xElement.Remove(); xElement.SetValue(null); Fagdag, 20.november 2009 Side 14

Manipulere xml: Remove attribute xElement.Remove(); xElement.Attribute("someAttribute").Remove(); xElement.RemoveAttributes(); xElement.RemoveAll(); xElement.SetAttributeValue("someAttribute", null); Fagdag, 20.november 2009 Side 15

Spørringer ScottGu Blog Weblogs.ASP.NET Main Feed Bozo Blog Fagdag, 20.november 2009 Side 16

Spørringer var allElementsInXml = from element in rssXml.Descendants() select element; Fagdag, 20.november 2009 Side 17

Spørringer var feedUrls = from url in rssXml.Descendants("Url") select url; Fagdag, 20.november 2009 Side 18

Spørringer var disabledFeeds = from feed in rssXml.Descendants("Feed") where (feed.Attribute("status")!= null && feed.Attribute("status").Value.Equals("disabled")) select feed.Descendants("Url"); Fagdag, 20.november 2009 Side 19

Spørringer var feeds = from feed in rssXml.Descendants("Feed") where feed.Attribute("status") == null || feed.Attribute("status").Value != "disabled" select new FeedDefinition { Name = feed.Element("Name").Value, Url = feed.Element("Url").Value }; IList feedList = feeds.ToList(); Fagdag, 20.november 2009 Side 20

Spørringer ScottGu Blog LINQ VS2008 Fagdag, 20.november 2009 Side 21

Spørringer: sub-queries var feeds = from feed in rssXml.Descendants("Feed") select new FeedDefinition { Name = feed.Element("Name").Value, Url = feed.Element("Url").Value, Tags = (from tag in feed.Elements("Tag") orderby tag.Value select tag.Value).ToList() }; Fagdag, 20.november 2009 Side 22

Validere mot XmlSchema XmlSchemaSet schemas = new XmlSchemaSet(); schemas.Add(”MyTargetNameSpace", ”MyXmlSchema.xsd"); xmlDocument.Validate(schemas, MyValidationEventHandler); Fagdag, 20.november 2009 Side 23

Tips: Refaktorer komplekse spørringer var feeds = from feed in rssXml.Descendants("Feed“) select new FeedDefinition { Name = feed.Element("Name").Value, Url = feed.Element("Url").Value, Tags = GetTags(feed) }; private IList GetTags( XElement feed ) { var tags = from tag in feed.Elements("Tag”) orderby tag.Value select tag.Value; return tags.ToList(); } Fagdag, 20.november 2009 Side 24

Andre tips & triks  Bruk lambda-uttrykk i spørringer  Count vs Any  Avg er følsomt for lange elementlister  Cast til list for å fjerne IQueryable-context Fagdag, 20.november 2009 Side 25

Ressurser    custom-rss-feed-reader-with-it.aspx custom-rss-feed-reader-with-it.aspx  Fagdag, 20.november 2009 Side 26

Spørsmål? Fagdag, 20.november 2009 Side 27

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