LINQ allows querying different data sources using a common syntax. It includes LINQ to Objects, LINQ to XML, and LINQ to SQL. Queries can be written using query syntax or method syntax, which ultimately gets compiled to method syntax. Common LINQ methods include Where, Select, GroupBy, Join, Max, and Average. Query syntax is usually simpler and more readable than method syntax, though there is no semantic difference. The var type is implicitly typed based on the right side expression. Lambda expressions allow inline anonymous methods and are useful for certain LINQ queries only expressible in method syntax. Expression lambdas specify an expression on the right side of =>.

1. Introduction to LINQ
Reporter : Peter

2. What is LINQ
• LINQ : language integrated query
• 可以使用一種相同的查詢方式來查詢不同的資料來源
• 有 LINQ TO OBJECTS, LINQ TO XML LINQ TO SQL
• 有兩種寫法 : query syntax , method syntax

4. • Query syntax 寫好的 linq statement 最終都會被 compile 成 method syntax
( 因為 .net CLR 無法理解 query syntax)
常用的 method syntax 有 :Where, Select, GroupBy, Join, Max, Average
In general, we recommend query syntax because it is usually simpler and more readable;
however there is no semantic difference between method syntax and query syntax. In
addition, some queries, such as those that retrieve the number of elements that match a
specified condition, or that retrieve the element that has the maximum value in a source
sequence, can only be expressed as method calls

5. 新型態 var
• Var 是一種後決議型別 (compile 時才知道他是屬於哪種類型 )
• 它的型別是由右方的運算式運算過後才可得知
• 所以在無法事先預知查詢 statement 會回傳甚麼型態時 , 就可以使用
var 取代真正的 type(for annoymous class)

7. What is extension method(since c#3.0)

8. Lambda expression
• To create a lambda expression, you specify input parameters (if any) on the
left side of the lambda operator =>, and you put the expression or statement
block on the other side.
• For example, the lambda expression x => x * x specifies a parameter that’s
named x and returns the value of x squared.

9. • the Where method: Where(num => num % 2 == 0). This inline expression is called a lambda
expression. It is a convenient way to write code that would otherwise have to be written in more
cumbersome form as an anonymous method or a generic delegate or an expression tree. In
C# => is the lambda operator, which is read as "goes to". The num on the left of the operator is
the input variable which corresponds to num in the query expression. The compiler can infer the
type of num because it knows that numbers is a generic IEnumerable<T> type. The body of the
lambda is just the same as the expression in query syntax or in any other C# expression or
statement; it can include method calls and other complex logic. The "return value" is just the
expression result.
• To get started using LINQ, you do not have to use lambdas extensively. However, certain queries
can only be expressed in method syntax and some of those require lambda expressions. After
you become more familiar with lambdas, you will find that they are a powerful and flexible tool in
your LINQ toolbox.

10. Expression Lambdas
• A lambda expression with an expression on the right side is called
an expression lambda.
• ( input parameters ) => expression
• Ex: ( x, y ) => x + y
• (int x, string s ) => s.Length > x