LINQ and C# 3.0 Mads Torgersen Program Manager for the C# Language Microsoft Corporation

from c in db.Customers where c.City == “London” select new { c.Name, c.Address }

LINQ Architecture Objects XML Relational LINQ enabled data sources LINQ To Objects LINQ To XML LINQ enabled ADO.NET VBOthers… LINQ To Entities LINQ To SQL LINQ To Datasets.Net Language Integrated Query (LINQ) C#

C# 3.0 Language Extensions var contacts = from c in customers where c.State == "WA" select new { c.Name, c.Phone }; var contacts = customers.Where(c => c.State == "WA").Select(c => new { c.Name, c.Phone }); Extension methods Lambda expressions Query expressions Object initializers Anonymous types Local variable type inference

Language Integrated Query

Querying in Visual C# 3.0 Extension methods – call static as instance Lambda expressions – inline methods Query expressions – querying made simple Implicitly typed locals – save the typing Anonymous types – temporary results

Standard Query Operators Restrict s.Where(…) Project s.Select(…), s.SelectMany(…) Order s.OrderBy(…).ThenBy(…) … Group s.GroupBy(…) Quantify s.Any(…), s.All(…) Partition s.TakeFirst(…), s.SkipFirst(…) Set s.Distinct(), s.Union(…), s.Intersect(…), s.Except(…) Singleton s.Element(…), s.ElementAt(…) Aggregate s.Count(), s.Sum(), s.Min(), s.Max(), s.Average(), s.Aggregate() Convert s.ToArray(), s.ToList() Cast s.OfType (), s.Cast s.OfType (), s.Cast

DLinq for Relational Data SqlConnection c = new SqlConnection(…); c.Open(); SqlCommand cmd = new c.Name, c.Name, c.Phone FROM Customers c FROM Customers c WHERE c.City WHERE c.City = "London"; DataReader dr = c.Execute(cmd); while (dr.Read()) { string name = r.GetString(0); string name = r.GetString(0); string phone = r.GetString(1); string phone = r.GetString(1); DateTime date = r.GetDateTime(2); DateTime date = r.GetDateTime(2);}r.Close(); Accessing data today Queries in quotes Loosely bound arguments Loosely typed result sets No compile time checks

public class Customer { … } public class Northwind: DataContext { public Table Customers; public Table Customers; …} Northwind db = new Northwind(…); var contacts = from c in db.Customers from c in db.Customers where c.City == "London" where c.City == "London" select new { c.Name, c.Phone }; select new { c.Name, c.Phone }; DLinq for Relational Data Accessing data with DLinq Classes describe data Strongly typed connection Integrated query syntax Strongly typed results Tables are like collections

XLinq for XML Data XmlDocument doc = new XmlDocument(); XmlElement contacts = doc.CreateElement("contacts"); foreach (Customer c in customers) if (c.Country == "USA") { if (c.Country == "USA") { XmlElement e = doc.CreateElement("contact"); XmlElement e = doc.CreateElement("contact"); XmlElement name = doc.CreateElement("name"); XmlElement name = doc.CreateElement("name"); name.InnerText = c.CompanyName; name.InnerText = c.CompanyName; e.AppendChild(name); e.AppendChild(name); XmlElement phone = doc.CreateElement("phone"); XmlElement phone = doc.CreateElement("phone"); phone.InnerText = c.Phone; phone.InnerText = c.Phone; e.AppendChild(phone); e.AppendChild(phone); contacts.AppendChild(e); contacts.AppendChild(e); }doc.AppendChild(contacts); Programming XML today <contacts> Great Lakes Food Great Lakes Food (503) (503) …</contacts> Imperative model Document centric No integrated queries Memory intensive

XLinq for XML Data XElement contacts = new XElement("contacts", from c in customers from c in customers where c.Country == "USA" where c.Country == "USA" select new XElement("contact", select new XElement("contact", new XElement("name", c.CompanyName), new XElement("name", c.CompanyName), new XElement("phone", c.Phone) new XElement("phone", c.Phone) )); Programming XML with XLinq Declarative model Element centric Integrated queries Smaller and faster

LINQ Extensibility New data sources Implement the LINQ pattern New languages Unified querying experience Expression tree generation Unified call syntax Query syntax

Try it!

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