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LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
LINQ Inside
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LINQ Inside

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  • 1. LINQ Inside 赵劼 http://jeffreyzhao.cnblogs.com jeffz@live.com
  • 2. About Me • Shanghai Baisheng Technology Co., Ltd. • Architect? Programmer! – Be a happy programmer • 日写代码三百行,不辞长作程序员 • Have fun with the technology • Good at losing weight. – Lost 40kg in 10 months
  • 3. The session is for you if… • You know nothing about LINQ. • You don’t like LINQ. • You want to learn how LINQ works in real world. • You’re not using LINQ for any reasons
  • 4. Agenda • LINQ and the related things • LINQ inside. • Performance tips • Advanced usages • Others
  • 5. What’s LINQ • Is it just a db access technology? • Is it just a piece of “syntactic sugar”?
  • 6. NO!
  • 7. “I’ll never use C# without LINQ” - Dflying Chen CTO Shanghai Baisheng Tech Co., Ltd.
  • 8. var odd = from i in new int[] { 1, 2, 3, 4, 5 } where i % 2 != 0 select i; WHAT’S LINQ
  • 9. About LINQ • Language Integrated Query • Since .NET Framework 3.5 with C# 3.0/VB 9.0 • The technology combined serveral others – Extension Method – Lambda Expression – Anonymous Method – Anonymous Class – etc.
  • 10. LINQ to… • LINQ != LINQ to SQL – A new way to access and manipulate data – Not only the data in SQL Server • What can we “LINQ to”? – LINQ to SQL – LINQ to XML – LINQ to Object – LINQ to Entity (from MS ADO.NET Entity Fx) • And we can also…
  • 11. LINQ to… (Cont.) • LINQ to Google • LINQ to System Search • LINQ to NHibernate • LINQ to Active Directory • LINQ to Lucene • LINQ to Flickr • LINQ to Excel • and more and more and more…
  • 12. Some Concerpts • LINQ • LINQ to SQL • LINQ Provider • http://jeffreyzhao.cnblogs.com/archive/2008/ 06/04/ajax-linq-lambda-expression.html
  • 13. Extension Method Anonymous Method Lambda Expression Anonymous Class … THINGS RELATED TO LINQ
  • 14. Extension Method • “syntactic sugar” – I agree with that. • More elegant programming style public static class StringExtensions{ public static string HtmlEncode(this s){ return HttpUtility.HtmlEncode(s); } <%= } HttpUtility.HtmlEncode( "<script>…</script>") => %> <%= "<script>…</script>".HtmlEnocde(); %>
  • 15. Anonymous Method • Inline delegates without method declaration • Can easily access the local variables – Magic of compiler void SomeMethod { int intVar; Action action = delegate() { intVar = 10; }; action(); }
  • 16. Lambda Expression • Functional programming style • “=>” operator • A lambda expression can represent: – An anonymous method – An expression tree – http://jeffreyzhao.cnblogs.com/archive/2008/06/ 04/ajax-linq-lambda-expression.html
  • 17. Things below are all equivalent Func<int, int, bool> predicate = delegate(int x, int y) { return x > y; }; Func<int, int, bool> predicate = (x, y) => { return x > y; }; Func<int, int, bool> predicate = (x, y) => x > y;
  • 18. And we can do more like… Func<int, int, bool> predicate = (x, y) => { var dayService = new DayService(); if (dayService.IsApirlFools(DateTime.Today)){ return x < y; } else { return x > y; } };
  • 19. Extension Method Lambda Expression for Anonymous method DEMO 1
  • 20. Expression Tree • A GREAT way to represent in lots of scenarios • Can be constructed by lambda expression in compile time • Can also be constructed programically – Lambda expression would be convert to this by compiler System.Linq.Expressions.Expression<TDelegate>
  • 21. Expression Tree Samples Expression<Func<int>> constantExpr = () => 5; Expression<Func<int, int, int>> simpleExpr = (x, y) => x + y; Expression<Func<int, int, bool>> complexExpr = (x, y) => new Random(DateTime.Now.Millisecond).Next(x) > y;
  • 22. Programmically Construction • See what complier do for us… Expression<Func<int, int>> negateExpr = x => -x; ParameterExpression param = Expression.Parameter(typeof(int), "x"); Expression<Func<int, int>> negateExpr = Expression.Lambda<Func<int, int>>( Expression.Negate(param), new ParameterExpression[] { param });
  • 23. Expression Hierarchy System.Linq.Expressions.Expression BinaryExpression ConditionalExpression ConstantExpression InvocationExpression LambdaExpression MemberExpression MethodCallExpression NewExpression NewArrayExpression MemberInitExpression ListInitExpression ParameterExpression TypeBinaryExpression UnaryExpression
  • 24. The Factory Methods • There’re factory methods in Expression class for us to build an Expression Tree. • Examples – New: Creates a NewExpression. – Negate: Creates a UnaryExpression that represents an arithmetic negation operation – And: Creates a BinaryExpression that represents a bitwise AND operation. – ArrayIndex: Creates an Expression that represents applying an array index operator.
  • 25. Tips of Construct Expression Trees • Process – Preparing parameter expressions at first. – Construct the body of expression tree with the factory methods. – Wrap the whole expression body with LambdaExpression at the end. • Tools can help us – Expression Tree Visualizer – .NET Reflector (a must-have for .NET programmer)
  • 26. Lambda Expression for Expression Tree Construct an Expression Tree Programically DEMO 2
  • 27. Question • What’s the difference between these two? var intList = new List<int>() { 1, 2, 3, 4, 5 }; foreach (int i in intList.Where(i => i % 2 == 1)) { Console.WriteLine(i); } var intList = new List<int>() { 1, 2, 3, 4, 5 }.AsQueryable(); foreach (int i in intList.Where(i => i % 2 == 1)) { Console.WriteLine(i); }
  • 28. Answer: • The lambda expression in the first code snippet represents an Anonymous Method • The lambda expression in the second code snippet constructs an Expression Tree
  • 29. Now we know about Extension Method and Lambda Expression, but… Where’s LINQ?
  • 30. Please wait for the second part of the session… 
  • 31. Next, We’ll Focus More on… • LINQ – Usage – Pros & Cons • Performance – Benchmark – Improvements • Advanced topics – Use Expression Tree in different scenarios. – LINQ Provider • Others
  • 32. References • http://msdn.microsoft.com • http://en.wikipedia.org/wiki/Linq • http://rednaxelafx.javaeye.com/blog/237822 • http://code.msdn.microsoft.com/csharpsampl es

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