This set of slides was used by Ralf Laemmel for a CHOOSE Talk on 05.03.2008

2. Why LINQ? Because: Data != Objects Aka the Bermuda Triangle of data processing Objects XML Relations

4. Database access in pre-LINQ era SqlConnection c = new SqlConnection(…); c.Open(); SqlCommand cmd = new SqlCommand( @“SELECT c.Name, c.Phone FROM Customers c WHERE c.City = @p0” ); cmd.Parameters[“@po”] = “London”; DataReader dr = c.Execute(cmd); while (dr.Read()) { string name = r.GetString(0); string phone = r.GetString(1); DateTime date = r.GetDateTime(2); } r.Close(); Queries in quotes Arguments loosely bound Results loosely typed Compiler cannot help catch mistakes

5. Database access with LINQ to SQL public class Customer { public int Id; public string Name; public string Phone; … } Table<Customer> customers = db.Customers; var contacts = from c in customers where c.City == &quot;London&quot; select new { c.Name, c.Phone }; Classes describe data Tables are real objects Query is natural part of the language Results are strongly typed

6. XML access in pre-LINQ era public static double XmlOrder2Total(XmlDocument doc) { static string ons = &quot;http://www.vertical.com/Order&quot;; double total = 0.0; XmlElement o = (XmlElement)doc.GetElementsByTagName(&quot;Order&quot;, ons).Item(0); foreach (XmlElement x in o.GetElementsByTagName(&quot;Item&quot;, ons)) { XmlNode priceNode = x.GetElementsByTagName(&quot;Price&quot;, ons).Item(0); XmlNode quantityNode = x.GetElementsByTagName(&quot;Quantity&quot;, ons).Item(0); double priceValue = Double.Parse(priceNode.InnerText); int quantityValue = Int32.Parse(quantityNode.InnerText); total += priceValue * quantityValue; } return total; } Imperative aggregation Low-level namespace model Verbose query API Tedious conversions

7. XML access with LINQ to XML public static double XmlOrder2Total(XElement o) { static XNamespace ons = &quot;http://www.vertical.com/Order&quot;; return (from item in o.Elements(ons + &quot;Item&quot;) select (double)item.Element(ons + &quot;Price&quot;) * (int)item.Element(ons + &quot;Quantity&quot;) ).Sum(); } Functional aggregation Designated type for namespaces SQL/XQuery like query syntax Concise accessors

8. Language INtegrated Query (LINQ) LINQ provides one programming model for all types of data (objects, SQL, XML, DataSets) LINQ enabled data sources LINQ To Objects Objects LINQ To XML <book> <title/> <author/> <price/> </book> XML LINQ enabled ADO.NET LINQ To Datasets LINQ To SQL LINQ To Entities Relational Others… VB C# .NET Language-Integrated Query

9. .NET through the ages

10. The evolution of C# C# 1.0 C# 2.0 C# 3.0 Components on a Managed Runtime Generics Language Integrated Query

12. C# 3.0 language innovations var contacts = from c in customers where c.City == &quot;Redmond&quot; select new { c.Name, c.Phone }; var contacts = customers .Where(c => c.City == &quot;Redmond&quot;) .Select(c => new { c.Name, c.Phone }); Extension methods Lambda expressions Query expressions Object initializers Anonymous types Local variable type inference

13. Local variable type inference Not to be confused with Pascal

14. Object initializers Field or property assignments

15. Anonymous types class ??? { public string Name; public int Age; } ???

16. Anonymous types class ??? { public string Name; public string Phone; } public class Customer { public string Name; public Address Address; public string Phone; … } public class Contact { public string Name; public string Phone; } Customer c = GetCustomer(…); Contact x = new Contact { Name = c.Name, Phone = c.Phone }; Customer c = GetCustomer(…); var x = new { c.Name, c.Phone }; Customer c = GetCustomer(…); var x = new { Name = c.Name, Phone = c.Phone }; Projection style initializer

17. Lambda expressions – motivating example Delegate type (function type) Higher-order function

18. Lambda expressions (not yet) Non-anonymous function

19. Lambda expressions (C# 1.0/2.0)

20. Lambda expressions (C# 3.0 sugar) Lambda expression

21. Lambda expressions (w/ type inference) Lambda expression

22. Extension methods Static method with “this” argument Invoke It like an instance method

24. Query expressions from id in source { from id in source | join id in source on expr equals expr [ into id ] | let id = expr | where condition | orderby ordering , ordering , … } select expr | group expr by key [ into id query ] Starts with from Zero or more from , join , let , where , or orderby Ends with select or group by Optional into continuation

25. Standard Query Operators Restriction Where Projection Select, SelectMany Ordering OrderBy, ThenBy Grouping GroupBy Quantifiers Any, All Partitioning Take, Skip, TakeWhile, SkipWhile Sets Distinct, Union, Intersect, Except Elements First, FirstOrDefault, ElementAt Aggregation Count, Sum, Min, Max, Average Conversion ToArray, ToList, ToDictionary Casting OfType<T>

26. Extension methods and queries namespace System.Linq { public static class Enumerable { public static IEnumerable<T> Where<T>(this IEnumerable<T> source, Func<T, bool> predicate) { … } public static IEnumerable<S> Select<T, S>(this IEnumerable<T> source, Func<T, S> selector) { … } … } } using System.Linq; Extension methods IEnumerable<string> contacts = customers.Where(c => c.State == &quot;WA&quot;).Select(c => c.Name); Brings extensions into scope obj.Foo(x, y)  ???.Foo(obj, x, y) IntelliSense!

27. Expression trees

28. LINQ architecture System.Linq.Enumerable Delegate based Source implements IEnumerable<T> System.Linq.Queryable Expression tree based Source implements IQueryable<T> SQL DataSets Objects Others…

29. LINQ to SQL Architecture Enumerate SQL Query or SProc Rows Objects SubmitChanges() DML or SProcs Application LINQ to SQL from c in db.Customers where c.City == &quot;London&quot; select c.CompanyName SELECT CompanyName FROM Customer WHERE City = 'London' db.Customers.Add(c1); c2.City = “Seattle&quot;; db.Customers.Remove(c3); INSERT INTO Customer … UPDATE Customer … DELETE FROM Customer …

32. Demo