Chuyên đề phát triển phần mềm LINQ remoting ppt

Week 4: LINQ
• Basic concepts
– LINQ requirements
– Concepts
• Types
– LINQ to objects
– LINQ to SQL
– LINQ to Entity
– LINQ to XML
2. New features in langauge
• Generics
• Implicitly Typed Variables
• Object Initializers
• Anonymous Types
• Extension Methods
• Lambda Expressions
2.0 Generics
• the creation of various types of
collection
• type safety
• Binary Code Reuse
– using System.Collections.Generic;
2.1 Implicitly Typed Variables
• Implicitly Typed Variables
– Declare variables without specifying their type
– Strongly type, not variant, not object
– VS will determinr type
• Predict what the compiler will choose
• Intellisense support
– Type inference -> most general
• “3/10/2010” -> string, not date

2.1 Implicitly Typed Variables
• Example
var x = new OledbConnection();
2.1 Implicitly Typed Variables
• Note
– Alwayls declare the type if we know
– Implicitly Typed Variables are suited for LINQ and
anonymous type
2.2 Object Initializers
• Constructor
• Allow to assign values to object properties
(fields) when create object
• We do not have to explicitly invoke a
constructor
• Usefull in any context
– Especially userfull in LINQ expressions
2.2 Object Initializers
• Example
2.3 Anonymous Types
• Implicitly type functionality for objects
– Set property values to object without writing
class definition
– The resulting class has no usable name
– Class name is generated by compiler, inherits
from Object
– The result: an anonymous type that is not
available at source code level
• Also called Projections
2.3 Anonymous Types
• When to user anonymous types

– Need a temporary object to hold related data
– Don’t need method
– If we need a different set of properties for each
declaration
– If we need to change the order of properties for
each declaration
2.3 Anonymous Types
• When not to user anonymous types
– Need to define methods
– Need to define another variable
– Need to shared data across methods
2.4 Extension Methods
• Special kind of Static method
• Allow the addition of methods to an existing
class
– Without creating a new derived type
– Without re-compiling or modifying the original type
• Called The Same way regular methods are called
• Define in static class
2.4 Extension Methods
• Example
2.4 Extension Methods
• Example
2.4.a Delegate
• Delegate
– refers to method.
– When initialize a delegate, we initialize it with
method.
2.4.a delegate: example
2.4.a delegate: why

2.4.a delegate: why
2.4.a delegate: with anonymous
2.4.a delegate: with anonymous:
return to example
2.5 Lambda Expressions
• Lambda Expressions is an Anonymous function
– A funciton without a name
– Perform action , return a single value
– Can be used wherever a delegate type is valid
• Why?
– Allow a function’s caller to define the action
– Not just pass parameters
– Lambda expressions provide a clearer syntax for
anonymous delegates
2.5 Lambda Expressions: delegate
• Syntax
– parameters => expression
– a functional superset of anonymous methods
– Lambda expressions can "infer" parameter types,
even if you omit them
– Lambda expressions can use both statement
blocks and expressions
2.5 Lambda Expressions in C#
• Use lambda operator =>
– Read as “goes to”
– x=>x+3 if x=1 then 4 is returned
– X=> x==5: if x=5, True is returned
– (x,y)=> x+y if x=2, y=4 then 6 is returned
– (x,y)=>x==y if x=2, y=4 then False is returned
2.4.a lambda example

2.4.a delegate: turn back to
example: lambda