Applied Linq

2. Applied Linq Putting Linqto work

3. Introducing… • Class-A • Kennisprovider Microsoft development • Training • Coaching • http://www.class-a.nl • Alex Thissen • Trainer/coach • http://blog.alexthissen.nl

4. Agenda • About Linq and queries • Query providers and APIs • What it means to apply Linq • Language and code • Query execution • Recommendations • Architecture • Beyond Linq • Demos • Questions and discussion

5. Introducing Linq • Uniform way to write queries over data • Linq is about query keywords • Built into new languages C# 3.0 and VB 9.0 • Linq is about query operators • 40+ standard query operators are defined • Methods that operate in queries or act on its results Dim query = From c In customers _ Where c.Orders.Count > 100 _ Order By c.CompanyName Descending _ Select c var query = from c in customers where c.Orders.Count > 100 orderby c.CompanyName descending select c;

6. About Linq queries • Expressed in terms of CLR types • Objects that might or might not exist in-memory • Linq queries are not SQL queries at all • Compositional and hierarchical by nature • Arbitrary nesting of queries • Additional operators can be applied to query • Declarative instead of imperative • Tell what you want, not how • How is up to underlying implementation

7. Writing queries • Learn the keywords and operators • Not all operators have corresponding keywords or language integration • Number of keywords may vary per language • Some parts must be written with operators • Usually exposes lambda expressions • Queries can be done without keywords • Explicit dot notation (what compiler creates) • Sometimes FLWOS is overkill

8. Demos Getting familiar with Linq queries • Query operations: selection, projection, grouping • Using keywords and operators

9. Sources of data • Your data must come from somewhere • In-memory CLR objects • Database • XML • Other repositories: registry, Active Directory, … • Various flavors of Linq disclose certain type of data • Query syntax does not change per source • Set of keywords and operators available might be different

10. Linq to XML • Power of Linq brought to data in XML format • Perform queries over XML data • New element-centric API to manipulate XML • Faster alternative to System.Xml DOM API • Functional construction of XML data with query expressions

11. Linq to SQL • Generates object model to represent data • Mapping of CLR types to database tables • Object/Relational Mapping (OR/M) technology • 1:1 relationships between objects and tables • Translates Linq queries to SQL statements • Builds on ADO.NET and .NET Transactions • Persistence services • Automatic change tracking and identity management of objects • Updates by SQL statements or stored procedures

12. Two kinds of Linq

13. Query providers • Out-of-the-box providers in .NET 3.5: • Linq to Objects • Linq to SQL • Sources in query determine query providers • Affects keywords and operators you can use • Query providers can translate Linq queries to some implementation • Most providers come with Linq-enabled APIs • New object models to work with data • Linq to Objects has several: Linq to XML, DataSets

14. Demo Linq applied Scenario: WCF services using untyped Messages WPF Application WCF Service SOAP messages Linq to XML API Linq to XML WCF proxy Linq to SQL

15. New language features C# and VB • Linq keywords • Extension methods • Lambda expressions • Local variable inference • Object and collection initializers • Anonymous types • Automatic properties • Partial methods new new

16. Visual Basic 9.0 • Deep XML support • Express XPath axes with XML properties • Allows XML literals to appear inside of code root.<Customer> Direct child elementscustomer.@CompanyIDAttribute selectiondoc...<description> All descendants Dim fragment As XElement = _ <company> <city>Hedel</city> </company>

17. Visual Basic 9.0 • Gives you “expression holes” inside XML literals • Additional keywords • More freedom on order of keywords Dim query = _ From c In doc...<Customers> _ Select <customer ID=<%= c.@CustomerID %> > <%= customer.<Name> %> phone:<%= customer...<Phone>(0) %> </customer>

18. Demo Visual Basic • WCF sample revisited • Deep XML support

19. Deferred execution • Most Linq query providers are implemented using lazy evaluation • Composed query expressions do not execute immediately • Queries only execute when necessary • Performing an iteration over resultset • Using extension methods ToArray, ToList, ToLookup, ToDictionary • Using specific query operators, such as aggregates and set operators

20. More on deferred execution • Before execution queries can still be changed or expanded • Adding additional sequence operators, such as Distinct, Skip, Take • Manipulating expression tree • Expression trees are immutable • Reference assignments take deep tree copies

21. Changes to way you write code • Declarative • Far less looping constructs visible • Easier to read and to maintain • Methods returning query or its results • Remember deferred execution • Force execution of query • Hand over query for further manipulation • Query reuse

22. Linq and architecture System.Data.Linq

23. Architecture recommendations • Find out where and how your queries execute • Moment of execution • Local versus remote execution • Physical place/tier of query execution • Keep queries inside assemblies • Do not pass query expressions between layers • Anonymous types shouldn’t be return values • Think about important types up front • Use projections wisely

24. Other recommendations • Learn: • to write queries with and without keywords • new language features • Use whitepapers as reference • Translation of query keywords to operators • Evaluation details of operators • Do not overuse or abuse var keyword • Decreases readability and stops you from thinking: if you know exact type, specify it • It sometimes takes more keystrokes

25. Runtimes and frameworks for Linq providers * APIs * ADO.NET Entity Framework released out of bounds with .NET FX 3.5

26. Beyond .NET FX 3.5 • ADO.NET Entity Framework • Microsoft’s long-term vision on data • Brings query provider Linq to Entities • Parallel Linq (PLinq) • Passes parts of query to different cores in multicore/multiproc machine • Community query providers for Linq: • Linq to Amazon, LDAP, SharePoint, NHibernate, MySql, Flickr, … and more (to come) • Linq 2.0

27. Expanding on Linq • Linq-enable your existing API’s • Specifically for in-memory queries • Create extension methods that return an IEnumerable<T> object • Write your own query provider • Implement IQueryable<T> • Parse expression trees and translate nodes to different code or query language

28. References • Linq home page • Future versions of • C#, Visual Basic, Visual Studio • Recommended reading • Linq to XML beta 1 docs • Future: Linq 2.0, PLinq • Downloads • Linq May 2006 CTP (for Visual Studio 2005) • Visual Studio Orcas April 2007 Beta 1 and C#, VB samples • Reflector 5.0

29. Blogs • Microsoft Teams • C# • VB • ADO.NET • Individuals on Linq • General: Oakleaf Systems, Wes Dyer, Jomo Fisher • SQL: Mike Taulty • XML: Eric White

30. Summary • Linq is about query keywords and operators • Linq will change way you write your code • Linq to XML might be more important than you think • Is VB a better query language than C#? • Linq is extensible

31. Questions? ?