LINQ: Language Integrated Query ST Colloquium, 2008-05-15 Tom - - PowerPoint PPT Presentation

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LINQ: Language Integrated Query ST Colloquium, 2008-05-15 Tom - - PowerPoint PPT Presentation

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LINQ: Language Integrated Query ST Colloquium, 2008-05-15 Tom Lokhorst Brief example Brief example int[] nrs = {2, 3, 9, 1, 21, 3, 42}; Brief example int[] nrs = {2, 3, 9, 1, 21, 3, 42}; var q = from n in nrs where n < 5 select n * n;

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LINQ: Language Integrated Query

ST Colloquium, 2008-05-15 Tom Lokhorst

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Brief example

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Brief example

int[] nrs = {2, 3, 9, 1, 21, 3, 42};

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Brief example

int[] nrs = {2, 3, 9, 1, 21, 3, 42}; var q = from n in nrs where n < 5 select n * n;

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Brief example

int[] nrs = {2, 3, 9, 1, 21, 3, 42}; var q = from n in nrs where n < 5 select n * n; foreach (var i in q) { Console.WriteLine(i); }

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Brief example

int[] nrs = {2, 3, 9, 1, 21, 3, 42}; var q = from n in nrs where n < 5 select n * n; foreach (var i in q) { Console.WriteLine(i); }

LINQ

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Overview

The problem space LINQ in .NET 3.5 Deconstructing expressions Usages of LINQ Comparisons with other stuff

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Circles, Triangles and Rectangles

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Circles, Triangles and Rectangles

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Circles, Triangles and Rectangles

Business software deals with lots of different types of data: Objects Tree structures (XML) Relational

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Assignment

A web server should show a list of the top 5 memory-intensive processes.

Per process, show its name, and a description. There is a SQL database with descriptions for programs. The list should be in RSS format.

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A bit of History

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A bit of History

.NET 1.0 released early 2002 CLR 1.0, C# 1.0, VB 7 .0 Delegates: managed function pointers

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A bit of History

.NET 1.0 released early 2002 CLR 1.0, C# 1.0, VB 7 .0 Delegates: managed function pointers .NET 2.0 released late 2005 CLR 2.0, C# 2.0, VB 8.0 Generics, iterators, anonymous delegates

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A bit of History

.NET 1.0 released early 2002 CLR 1.0, C# 1.0, VB 7 .0 Delegates: managed function pointers .NET 2.0 released late 2005 CLR 2.0, C# 2.0, VB 8.0 Generics, iterators, anonymous delegates .NET 3.5 released late 2007 CLR 2.0, C# 3.0, VB 9.0 Lambda expressions, local type inferencing, extension methods, LINQ

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LINQ in .NET 3.5

Libraries LINQ to Objects LINQ to XML LINQ to SQL Language enhancements Lambda expressions Query syntax Compiler enhancements Expression trees

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LINQ to Objects

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Eating the sugar

var q = from n in nrs where n < 5 select n * n; int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 3.0

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Eating the sugar

IEnumerable<int> q = from n in nrs where n < 5 select n * n; int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 3.0

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Eating the sugar

IEnumerable<int> q = nrs.Where<int>(n => n < 5) .Select<int, int>(n => n * n); int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 3.0

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Eating the sugar

IEnumerable<float> q = nrs.Where<int>(n => n < 5) .Select<int, float>(n => n * 0.5F); int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 3.0

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Eating the sugar

IEnumerable<float> q = Enumerable.Select<int, float>( Enumerable.Where<int>(nrs, n => n < 5), (n => n * 0.5F)); int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 3.0

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Eating the sugar

IEnumerable<float> q = Enumerable.Select<int, float>( Enumerable.Where<int>(nrs, n => n < 5), (n => n * 0.5F)); int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 3.0 public static IEnumerable<T> Where<T>(this IEnumerable<T> source, Func<T, bool> predicate) { ... }

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Eating the sugar

IEnumerable<float> q = Enumerable.Select<int, float>( Enumerable.Where<int>(nrs, n => n < 5), (n => n * 0.5F)); int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 3.0 public static IEnumerable<T> Where<T>(this IEnumerable<T> source, Func<T, bool> predicate) { foreach (var elem in source) if (predicate(elem)) yield return elem; }

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Eating the sugar

IEnumerable<float> q = Enumerable.Select<int, float>( Enumerable.Where<int>(nrs, n => n < 5), (n => n * 0.5F)); int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 3.0

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Eating the sugar

IEnumerable<float> q = Enumerable.Select<int, float>( Enumerable.Where<int>(nrs, delegate(int n){ return n < 5; }), delegate(int n){ return n * 0.5F;} ); int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 2.0

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Eating the sugar

IEnumerable<float> q = Enumerable.Select<int, float>( Enumerable.Where<int>(nrs, new Func<int, bool>(LessThanFive)), new Func<int, float>(TimesHalf) ); bool LessThanFive(int n) { return n < 5; } float TimesHalf(int n) { return n * 0.5F; } int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 1.0*

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Eating the sugar

var q = from n in nrs where n < 5 select n * n; int[] nrs = {2, 3, 9, 1, 21, 3, 42}; C# 3.0

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LINQ to Objects

Query comprehenssions More syntax; orderby, groupby, join Works on you data structures IEnumerable<T> Implement you own Where<T>, Select<T> More library functions

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LINQ to XML

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Dealing with angle brackets

LINQ to XML is a replacement for the W3C Document Object Model, because: It’ s old It’ s ugly It’ s impractical New API, all library: System.Xml.LINQ

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Document Object Model

Imperative API Document-centric Weird data types

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Document Object Model

Imperative API Document-centric Weird data types

<Company name=”Microsoft”> <Founders> <Person>Bill Gates</Person> </Founders> </Company>

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Document Object Model

XmlDocument doc = new XmlDocument(); XmlElement company = doc.CreateElement("Company"); doc.AppendChild(company); XmlAttribute name = doc.CreateAttribute("name"); name.Value = "Microsoft"; company.Attributes.Append(name); XmlElement founders = doc.CreateElement("Founders"); company.AppendChild(founders); XmlElement person = doc.CreateElement("Person"); founders.AppendChild(person); XmlText bill = doc.CreateTextNode("Bill Gates"); person.AppendChild(bill);

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LINQ to XML

Functional construction Element-centric (context free) CLR data types (collection friendly)

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LINQ to XML

XElement company = new XElement("Company", new XAttribute("name", "Microsoft"), new XElement("Founders", new XElement("Person", "Bill Gates") ) );

Functional construction Element-centric (context free) CLR data types (collection friendly)

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XML with queries

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XML with queries

string[] names = { “Anders”, “Erik”, “Amanda” };

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XML with queries

string[] names = { “Anders”, “Erik”, “Amanda” }; from n in names where n.StartsWith(“A”) select new XElement(“Person”, n)

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XElement employees = new XElement(“Employees”, );

XML with queries

string[] names = { “Anders”, “Erik”, “Amanda” }; from n in names where n.StartsWith(“A”) select new XElement(“Person”, n)

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XElement employees = new XElement(“Employees”, );

XML with queries

string[] names = { “Anders”, “Erik”, “Amanda” }; from n in names where n.StartsWith(“A”) select new XElement(“Person”, n) company.Add(employees);

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XElement employees = new XElement(“Employees”, );

XML with queries

string[] names = { “Anders”, “Erik”, “Amanda” }; from n in names where n.StartsWith(“A”) select new XElement(“Person”, n) company.Add(employees); Console.WriteLine(company);

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XML on the Console

<Company name=”Microsoft”> <Founders> <Person>Bill Gates</Person> </Founders> <Employees> <Person>Anders</Person> <Person>Amanda</Person> </Employees> </Company>

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IEnumerable<string> persons = from p in company.Descendants(“Person”) select p.Value;

Querying XML

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IEnumerable<string> persons = from p in company.Descendants(“Person”) select p.Value;

Querying XML

Bill Gates Anders Amanda

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LINQ to SQL

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Querying a SQL backend

Use LINQ to query a relational database Strongly typed queries Remote the query to the DBMS C# must remain API/DB independent

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LINQ to SQL

Simple Object Relational Mapper Microsoft SQL Server Comes with tool to make classes out of tables in an existing database Certainly not the best ORM out there More advanced stuff: LINQ to Entities

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LINQ to SQL example

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LINQ to SQL example

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LINQ to SQL example

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LINQ to SQL example

[DatabaseAttribute(Name="Northwind")] public partial class NorthwindDataContext : System.Data.LINQ.DataContext { public NorthwindDataContext() : base("Data Source=.;Initial Catalog=Northwind;" + "Integrated Security=True") { } public Table<Customer> Customers { get { return this.GetTable<Customer>(); } } }

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LINQ to SQL example

[Table(Name="dbo.Customers")] public partial class Customer : INotifyPropertyChanging, INotifyPropertyChanged { private string _CustomerID; [Column(Storage="_CustomerID", DbType="NChar(5) NOT NULL", CanBeNull=false, IsPrimaryKey=true)] public string CustomerID { get { return this._CustomerID; } set { /* Setter code removed */ } } /* More code be here */ }

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LINQ to SQL example

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LINQ to SQL example

var db = new NorthwindDataContext(); var q = from c in db.Customers where c.City == “London” select c;

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LINQ to SQL example

var db = new NorthwindDataContext(); var q = from c in db.Customers where c.City == “London” select c; foreach (var c in q) Console.WriteLine(c.CustomerID + “ “ + c.ContactName);

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LINQ to SQL example

var db = new NorthwindDataContext(); var q = from c in db.Customers where c.City == “London” select c; foreach (var c in q) Console.WriteLine(c.CustomerID + “ “ + c.ContactName); AROUT Thomas Hardy BSBEV Victoria Ashworth CONSH Elizabeth Brown EASTC Ann Devon NORTS Simon Crowther SEVES Hari Kumar

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LINQ to SQL example

var q = db.Customers.Where<Customer>( c => c.City == “London”);

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Lambdas again

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Lambdas again

Func<int, int> f = x => (x + 1) * 2; int nr = f(20); Console.WriteLine(nr); // Prints: 42

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Lambdas again

Expression<Func<int, int>> e = x => (x + 1) * 2;

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Lambdas again

string str = e.NodeType + “ “ + e.Parameters.Count; Console.WriteLine(str); // Prints: Lambda 1 Expression<Func<int, int>> e = x => (x + 1) * 2;

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Lambdas again

string str = e.NodeType + “ “ + e.Parameters.Count; Console.WriteLine(str); // Prints: Lambda 1 Expression<Func<int, int>> e = x => (x + 1) * 2; Func<int, int> f = e.Compile(); Console.WriteLine(f(20)); // Prints: 42

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Lambdas again

Expression<Func<int, int>> e = x => (x + 1) * 2;

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Lambdas again

ParameterExpression x = Expression.Parameter(typeof(int), "x"); Expression one = Expression.Constant(1, typeof(int)); Expression two = Expression.Constant(2, typeof(int)); Expression body = Expression.Multiply(Expression.Add(x, one), two); Expression<Func<int, int>> e = Expression.Lambda<Func<int, int>>(body, x); Expression<Func<int, int>> e = x => (x + 1) * 2;

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LINQ to SQL example

var q = db.Customers.Where<Customer>( c => c.City == “London”);

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LINQ to SQL example

ParameterExpression c = Expression.Parameter(typeof(Customer), "c"); IQueryable<Customer> q = db.Customers .Where<Customer>(Expression.Lambda<Func<Customer, bool>>( Expression.Equal( Expression.Property(c, (MethodInfo) methodof(Customer.get_City)), Expression.Constant("London", typeof(string)), false, (MethodInfo) methodof(string.op_Equality)), c));

var q = db.Customers.Where<Customer>( c => c.City == “London”);

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LINQ to SQL example

var q = db.Customers.Where<Customer>( c => c.City == “London”); SELECT C.* FROM Customers AS C WHERE C.City = “London”

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Many more operations

int x = db.Customers.Where<Customer>( c => c.City == “London”).Count(); SELECT COUNT(C.*) AS value FROM Customers AS C WHERE C.City = “London”

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Many more operations

int x = db.Customers.Where<Customer>( c => c.City == “London”).Take(4); SELECT TOP (4) C.* FROM Customers AS C WHERE C.City = “London”

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Many more operations

Restriction Where Projection Select, SelectMany Partitioning Take, Skip, TakeWhile, SkipWhile Join Join, GroupJoin Concatinatin Concat Ordering OrderBy, ThenBy, Reverse Grouping GroupBy Set Distinct, Union, Intersect, Except Conversion ToArray, ToList, ToDictionary, OfType, Cast Elemement First, FirstOrDefault, Last, LastOrDefault Generation Range, Repeat, Empty Quantifiers Any, All, Contains Aggregate Count, Sum, Min, Max, Average, Aggregate

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Assignment

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Assignment

Solution

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Assignment

Solution

new XElement("rss", new XAttribute("version", "2.0"), new XElement("channel", new XElement("title", "Top Processes"), from p in (from p in Process.GetProcesses()

  • rderby p.VirtualMemorySize descending

select p).Take(5) join pd in db.ProcessDescriptions

  • n p.ProcessName equals pd.Name into descrs

from d in descrs.DefaultIfEmpty() select new XElement("item", new XElement("title", p.ProcessName), d != null ? new XElement("description", d.Description) : null) ) );

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Assignment

Solution

<rss version="2.0"> <channel> <title>Top Processes</title> <item> <title>sqlservr</title> <description>SQL Server</description> </item> <item> <title>sqlservr</title> <description>SQL Server</description> </item> <item> <title>devenv</title> <description>Visual Studio</description> </item> <item> <title>ssmsee</title> </item> <item> <title>Reflector</title> </item> </channel> </rss>

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Other providers

DbLinq (MySQL, PostgreSQL, Oracle) LINQ to Google LINQ to Entities Parallel LINQ DryadLINQ (Distributed execution engine)

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Concluding...

All LINQ is: Query comprehensions Libraries Expression trees Many more providers to come...

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Questions?

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Assignment in VB syntax

Dim result = _ <rss version="2.0"> <channel>Top Processes</channel> <%= From p In Process.GetProcesses() _ Order By p.VirtualMemorySize Descending _ Take 5 _ Group Join pd In db.ProcessDescriptions _ On p.ProcessName Equals pd.Name _ Into descrs = Group _ From d In descrs.DefaultIfEmpty _ Select <item> <title><%= p.ProcessName %></title> <%= If(d IsNot Nothing, _ <description><%= d.Description %></description>, _ Nothing) %> </item> %> </rss>

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LINQ in Java

// Setup a JPA entity manager... SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory(); EntityManagerFactory entityManagerFactory = new EntityManagerFactoryImpl(sessionFactory, PersistenceUnitTransactionType.RESOURCE_LOCAL, true); QueryableEntityManager entityManager = new QueryableEntityManager(entityManagerFactory.createEntityManager()); // Select all customers in the Washington region Iterable<Customer> waCustomers = from("c").in(entityManager.entity(Customer.class)). where(eq("c.getRegion()", "WA")). select("c");

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Monadic parser combinators using C#

public abstract class MiniMLParsers<TInput> : CharParsers<TInput>{ public MiniMLParsers() { Whitespace = Rep(Char(' ').OR(Char('\t').OR(Char('\n')).OR(Char('\r')))); WsChr = chr => Whitespace.AND(Char(chr)); Id = from w in Whitespace from c in Char(char.IsLetter) from cs in Rep(Char(char.IsLetterOrDigit)) select cs.Aggregate(c.ToString(),(acc,ch) => acc+ch); Ident = from s in Id where s != "let" && s != "in" select s; LetId = from s in Id where s == "let" select s; InId = from s in Id where s == "in" select s; Term1 = (from x in Ident select (Term)new VarTerm(x)) .OR( (from u1 in WsChr('(') from t in Term from u2 in WsChr(')') select t)); Term = (from u1 in WsChr('\\') from x in Ident from u2 in WsChr('.') from t in Term select (Term)new LambdaTerm(x,t))

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Monadic parser combinators using C#

from cs in Rep(Char(char.IsLetterOrDigit)) select cs.Aggregate(c.ToString(),(acc,ch) => acc+ch); Ident = from s in Id where s != "let" && s != "in" select s; LetId = from s in Id where s == "let" select s; InId = from s in Id where s == "in" select s; Term1 = (from x in Ident select (Term)new VarTerm(x)) .OR( (from u1 in WsChr('(') from t in Term from u2 in WsChr(')') select t)); Term = (from u1 in WsChr('\\') from x in Ident from u2 in WsChr('.') from t in Term select (Term)new LambdaTerm(x,t)) .OR( (from letid in LetId from x in Ident from u1 in WsChr('=') from t in Term from inid in InId from c in Term select (Term)new LetTerm(x,t,c))) .OR( (from t in Term1 from ts in Rep(Term1) select (Term)new AppTerm(t,ts))); All = from t in Term from u in WsChr(';') select t; }