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LINQ Inside

              赵劼
http://jeffreyzhao.cnblogs.com
         jeffz@live.com
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
• ...
The session is for you if…
• You know nothing about LINQ.
• You don’t like LINQ.
• You want to learn how LINQ works in rea...
Agenda
•   LINQ and the related things
•   LINQ inside.
•   Performance tips
•   Advanced usages
•   Others
What’s LINQ
• Is it just a db access technology?
• Is it just a piece of “syntactic sugar”?
NO!
“I’ll never use C# without LINQ”
                                    - Dflying Chen
                                      ...
var odd =
  from i in new int[] { 1, 2, 3, 4, 5 }
  where i % 2 != 0
  select i;

WHAT’S LINQ
About LINQ
• Language Integrated Query
• Since .NET Framework 3.5 with C# 3.0/VB 9.0
• The technology combined serveral ot...
LINQ to…
• LINQ != LINQ to SQL
  – A new way to access and manipulate data
  – Not only the data in SQL Server
• What can ...
LINQ to… (Cont.)
•   LINQ to Google
•   LINQ to System Search
•   LINQ to NHibernate
•   LINQ to Active Directory
•   LINQ...
Some Concerpts
• LINQ
• LINQ to SQL
• LINQ Provider

• http://jeffreyzhao.cnblogs.com/archive/2008/
  06/04/ajax-linq-lamb...
Extension Method
Anonymous Method
Lambda Expression
Anonymous Class
…

THINGS RELATED TO LINQ
Extension Method
• “syntactic sugar” – I agree with that.
• More elegant programming style
                               ...
Anonymous Method
• Inline delegates without method declaration
• Can easily access the local variables
  – Magic of compil...
Lambda Expression
• Functional programming style
• “=>” operator
• A lambda expression can represent:
  – An anonymous met...
Things below are all equivalent

Func<int, int, bool> predicate = delegate(int x, int y) { return x > y; };


Func<int, in...
And we can do more like…

 Func<int, int, bool> predicate = (x, y) => {
     var dayService = new DayService();
     if (d...
Extension Method
Lambda Expression for Anonymous method

DEMO 1
Expression Tree
• A GREAT way to represent in lots of scenarios
• Can be constructed by lambda expression in
  compile tim...
Expression Tree Samples
Expression<Func<int>> constantExpr = () => 5;

Expression<Func<int, int, int>> simpleExpr = (x, y)...
Programmically Construction
• See what complier do for us…
   Expression<Func<int, int>> negateExpr = x => -x;




   Para...
Expression Hierarchy
System.Linq.Expressions.Expression
  BinaryExpression
  ConditionalExpression
  ConstantExpression
  ...
The Factory Methods
• There’re factory methods in Expression class for
  us to build an Expression Tree.
• Examples
  – Ne...
Tips of Construct Expression Trees
• Process
  – Preparing parameter expressions at first.
  – Construct the body of expre...
Lambda Expression for Expression Tree
Construct an Expression Tree Programically

DEMO 2
Question
• What’s the difference between these two?
  var intList = new List<int>() { 1, 2, 3, 4, 5 };
  foreach (int i in...
Answer:
• The lambda expression in the first code
  snippet represents an Anonymous Method
• The lambda expression in the ...
Now we know about Extension Method and
        Lambda Expression, but…

            Where’s LINQ?
Please wait for the
second part of the session…
            
Next, We’ll Focus More on…
• LINQ
  – Usage
  – Pros & Cons
• Performance
  – Benchmark
  – Improvements
• Advanced topics...
References
•   http://msdn.microsoft.com
•   http://en.wikipedia.org/wiki/Linq
•   http://rednaxelafx.javaeye.com/blog/237...
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Transcript of "LINQ Inside"

  1. 1. LINQ Inside 赵劼 http://jeffreyzhao.cnblogs.com jeffz@live.com
  2. 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. 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. 4. Agenda • LINQ and the related things • LINQ inside. • Performance tips • Advanced usages • Others
  5. 5. What’s LINQ • Is it just a db access technology? • Is it just a piece of “syntactic sugar”?
  6. 6. NO!
  7. 7. “I’ll never use C# without LINQ” - Dflying Chen CTO Shanghai Baisheng Tech Co., Ltd.
  8. 8. var odd = from i in new int[] { 1, 2, 3, 4, 5 } where i % 2 != 0 select i; WHAT’S LINQ
  9. 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. 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. 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. 12. Some Concerpts • LINQ • LINQ to SQL • LINQ Provider • http://jeffreyzhao.cnblogs.com/archive/2008/ 06/04/ajax-linq-lambda-expression.html
  13. 13. Extension Method Anonymous Method Lambda Expression Anonymous Class … THINGS RELATED TO LINQ
  14. 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. 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. 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. 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. 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. 19. Extension Method Lambda Expression for Anonymous method DEMO 1
  20. 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. 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. 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. 23. Expression Hierarchy System.Linq.Expressions.Expression BinaryExpression ConditionalExpression ConstantExpression InvocationExpression LambdaExpression MemberExpression MethodCallExpression NewExpression NewArrayExpression MemberInitExpression ListInitExpression ParameterExpression TypeBinaryExpression UnaryExpression
  24. 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. 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. 26. Lambda Expression for Expression Tree Construct an Expression Tree Programically DEMO 2
  27. 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. 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. 29. Now we know about Extension Method and Lambda Expression, but… Where’s LINQ?
  30. 30. Please wait for the second part of the session… 
  31. 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. 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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