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”?
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
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;
}
};
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>
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 });
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?
