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LINQ 全面透析 黃忠成資訊工作室

LINQ 全面透析 黃忠成資訊工作室. LINQ To Objects LINQ To XML LINQ To DataSet. LINQ To CLR. SQL Server Support O/R Mapping SQL Injection Prevent. LINQ. LINQ To SQL. Multi-Database Support O/R Mapping EDM SQL Injection Prevent. LINQ To Entities. VB.NET 2008 新語法. Partial Class

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LINQ 全面透析 黃忠成資訊工作室

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  1. LINQ 全面透析 黃忠成資訊工作室 • LINQ To Objects • LINQ To XML • LINQ To DataSet LINQ To CLR • SQL Server Support • O/R Mapping • SQL Injection Prevent LINQ LINQ To SQL • Multi-Database Support • O/R Mapping • EDM • SQL Injection Prevent LINQ To Entities

  2. VB.NET 2008新語法 • Partial Class • Partial Method • Anonymous Function Expression • Object Initialize

  3. 什麼是LINQ • LINQ全名為 • Language Integrated Query • Language指的是程式語言 • Integrated指的是整合 • Query指的是查詢 • 因此,LINQ就是[整合至程式語言中的查詢敘述語法] • 那些程式語言支援LINQ • C# 2008 • VB.NET 2008 • Ruby • Phyton

  4. 為什麼我們需要LINQ • 你是否需要在陣列中尋找一元素? • 你是否需要在陣列中尋找多個符合條件的元素 • 在LINQ前,你是怎麼做? • 迴圈與列舉一一比對是唯一方法 • 更好的方法,使用Delegate. • 在LINQ後,你能怎麼做? • 使用SQL LIKE語法,像查詢SQL資料庫般查詢陣列 • 像查詢SQL資料庫般,LINQ允許你對多個陣列進行JOIN並查詢

  5. LINQ To Objects

  6. 一個簡單的例子 傳統寫法 使用LINQ

  7. LINQ的設計初衷 • 提供一組常用的運算模組,例如搜尋,聯集(Join)搜尋,協助設計師完成日常的運算工作 • 透過程式語言與編譯器的協助,提供新的程式語法,將使用這個運算模組的動作,變成程式語言的一部份.

  8. LINQ的架構

  9. LINQ語法規則基礎 Alias Where 語句 查詢條件 FROM語句 DataSource

  10. LINQ的資料來源(Data Source) • 必須是實作IEnumerable(Of T)的物件 • 陣列 • Dim List As String() = {“code6421”, “tom”, “mary”} • List(Of T) • Dim Data = New List(Of String)() • 與.NET Framework結合應用 • Dim List = From S1 In Directory.GetFiles("C:\Windows") Where S1.Contains("w")

  11. 常用術語解釋 • Data Source,資料來源,元素集 • 一個實作IEnumerable(Of T)的物件 • 查詢回傳集 • 由查詢式回傳的物件 • 元素 • 回傳集,元素集中的某一元素 • 查詢式 • LINQ 語句

  12. 了解Where語句 • Where語句後? • 在LINQ To Objects中,Where語句後是一段程式碼 • Directory.GetFiles("C:\Windows") Where S1.Contains("w") S1.Contains(“w”)是一段回傳Boolean值的程式碼 • 同理,下面的寫法也是允許的 • AND • From s1 In List Where s1 Mod 5 = 0 And s1 > 20 • OR • From s1 In List Where s1 Mod 5 = 0 Or s1 > 20

  13. Contains函式的秘密 • From s1 In Data Where s1.Name.Contains(likeName) • s1 = String • String擁有Contains函式 • 所以,可以用s1.Contains來判別該元素是否擁有特定字元 • 同理 • From s1 In Data Where s1.Name.StartsWith(likeName) • 可以判定該元素是否以特定字元開始 • Contains的簡化式 • Dim result = From s1 In Data Where s1.Name Like "*V*" • Dim List As Integer() = {15, 20, 25, 30, 34} Dim Result = From s1 In List Where s1 Mod 5 = 0

  14. 了解Where語句2 • 定義函式 • From s1 In List Where Filter(s1) • 類別函式 • 類別靜態函式

  15. In查詢式

  16. Where語句於執行時期 • Where語句後的程式碼,會被編成一函式 • 當我們列舉查詢式回傳集中元素時(以For Each,For),每個元素都會被傳入此函式比對,以傳回值判定是否取回該元素或是跳過進行下一個元素之比對. • LINQ To Objects的重要觀念,有Where條件時 • 在開始列舉時,每一個元素都會被送往某一函式比對 • 模式與你用迴圈列舉相同.

  17. 排序 • 正向排序 • 倒序 • 多重排序

  18. Inner Query • Query 中可包含另一Query • Query As Data Source

  19. 了解Select語句 • Default Select • From s1 In Data • Explicit Select • From s1 In Data Select s1 • Select New • From s1 In Data Select Name = s1.Name + "," + s1.Age.ToString()

  20. JOIN

  21. JOIN的模式 • 預設為INNER JOIN,在JOIN時,左邊找到的,右邊也要找到,否則就不列出 • GROUP JOIN • 以GROUP JOIN模擬LEFT JOIN • 以GROUP JOIN模擬FULL OUTER JOIN

  22. Grouping • Simple Group • [Group <Data Source> By <key variable> = <key from Data Source> Into <Alias Variable> = Group Select <Anonymous Type>

  23. 另一個Group例子 • Group Alias Variable • Multi-Key Grouping

  24. 常用語句 • Take • Skip • Any • All

  25. Take • Take • 由查詢回傳集中取出特定元素 • TakeWhile • 由查詢回傳集中以特定條件比對,取出元素 From s1 In persons Take 2 From s1 In persons Take While s1.Age = 18 Or s1.Age = 28 • 注意! Take While是比對指定條件,當有元素不符合時,Take While就會結束,換句話說,當第一個元素之age不等於18或28時,Take While就會結束,即使第二三個元素符合條件.

  26. Skip • Skip • 跳過查詢回傳集中特定數量元素後開始取得元素 • Skip While • 跳過查詢回傳集中符合特定條件之元素後開始取得元素 From s1 In persons Skip 1 From s1 In persons Skip While s1.Age = 18 • 注意! Skip While是比對指定條件,當有元素不符合時,Ski While就會結束,換句話說,當第一個元素之age不等於18時,Skip While就會結束,列出所有元素,即使第二三個元素符合條件.

  27. Distinct • Distinct • 惕除查詢回傳集重複元素 Dim nums() = {1, 1, 3, 4, 5} Dim Result = From s1 In nums Distinct For Each item In Result Console.WriteLine(item) Next

  28. Aggregate 語句 • Aggregate 語法規則 • Any的例子(判斷元素集中是否包含符合條件的元素) • Any後的語句與Where後語句相同,是一段程式碼 Aggregate <alias> In <datasource> <Where> <Where Expression) Into <expression> Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 18, "002")) persons.Add(New Person("mary", 18, "002")) Dim Result = Aggregate s1 In persons Into p1 = Any(s1.Age = 18) Console.WriteLine(Result)

  29. Aggregate語句結合Where • Aggregate也可以與Where整合 • Aggregate也可以與Join整合

  30. Aggregate敘述重要觀念 • Aggregate通常傳回單值,例如Boolean,數值 • Aggregate後的語法與From…語句幾乎相同 • Aggregate可包含Where , Join , Group 等語句,與From..相同

  31. All • All的例子(判斷元素集中是否全數符合條件) • All後的語句與Where後語句相同,是一段程式碼 Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 18, "002")) persons.Add(New Person("mary", 18, "002")) Dim Result = Aggregate s1 In persons Into p1 = Any(s1.Age = 18) Console.WriteLine(Result)

  32. Average,Count • Average的例子(取平均值) • Count(取元素數) Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 28, "002")) persons.Add(New Person("mary", 19, "002")) Dim Result = Aggregate s1 In persons Into p1 = Average(s1.Age) Console.WriteLine(Result) Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 28, "002")) persons.Add(New Person("mary", 19, "002")) Dim Result = Aggregate s1 In persons Into p1 = Count(s1.Age >= 19) Console.WriteLine(Result)

  33. Min,Max • Min(取最小值) • Min(取最大值) Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 28, "002")) persons.Add(New Person("mary", 19, "002")) Dim Result = Aggregate s1 In persons Into p1 = Max(s1.Age) Console.WriteLine(Result) Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 28, "002")) persons.Add(New Person("mary", 19, "002")) Dim Result = Aggregate s1 In persons Into p1 = Min(s1.Age) Console.WriteLine(Result)

  34. Sum • Sum(加總) • Using Sum With Build-Type Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 28, "002")) persons.Add(New Person("mary", 19, "002")) Dim Result = Aggregate s1 In persons Into p1 = Sum(s1.Age) Console.WriteLine(Result) Dim nums() As Integer = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10} Dim Result = Aggregate s1 In nums Into p1 = Sum(s1) Console.WriteLine(Result)

  35. 以Group結合Sum運算 • Aggregate是傳回單值 • 如需傳回元素集,可使用Group語句進行 • 寫法與Aggregate後面敘述幾乎相同

  36. First • First • 取得第一個元素 • 如果沒有元素符合,First將會拋出例外 Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 28, "002")) persons.Add(New Person("mary", 19, "002")) Dim Result = (From s1 In persons Where s1.Age >= 18).First() Console.WriteLine(Result.Age)

  37. FirstOrDefault • FirstOrDefault • 當沒有元素時,回傳Nothing,但不引發例外 Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 28, "002")) persons.Add(New Person("mary", 19, "002")) Dim Result = (From s1 In persons Where s1.Age >= 50).FirstOrDefault() If Not Result Is Nothing Then Console.WriteLine(Result.Age) End If

  38. Last,LastOrDefault • Last • 取得查詢集的最後一個元素 • LastOrDefault • 同Last,但如果查詢集為空,那將回傳Nothing Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 28, "002")) persons.Add(New Person("mary", 19, "002")) Dim Result = (From s1 In persons Where s1.Age >= 18).Last() Console.WriteLine(Result.Age) Dim persons = New List(Of Person) persons.Add(New Person("code6421", 18, "001")) persons.Add(New Person("tom", 28, "002")) persons.Add(New Person("mary", 19, "002")) Dim Result = (From s1 In persons Where s1.Age >= 50).LastOrDefault() If Not Result Is Nothing Then Console.WriteLine(Result.Age) End If

  39. 查詢語句的回傳值 • 查詢語句的回傳值,多數是IEnumerable(Of T)型別 • IEnumerable(Of T)定義了First函式 • 一個關鍵例子 • Array並不是IEnumerable(Of T),為何有First函式? Dim nums() = {1, 2, 3, 4, 5} Dim Result = nums.First()

  40. Extension Method • 什麼是Extension Method • Extension Method必須定義在Module中 • 一個簡單的例子 • LINQ Framework就是一群Extension Method的結合

  41. LINQ與編譯器 • 使用Reflector 看我們的程式. • Extension Method是LINQ Framework的底層架構

  42. From LINQ Expression To Direct Call Extension Method • Function Expression 與 LINQ Extension Method • Distinct • Sum • Average • Min • Max • SkipWhile,TakeWhile

  43. Where And WhyLINQ Expression .VS. Direct Call • LINQ Expression的好處 • 直覺,與SQL語法類似 • 易讀 • LINQ Expression的缺點 • 敘述過長 • 受限於語法規則,無法達到Direct Call的相同效果 • 何時使用Direct Call • 對一元素集進行單一運算,例如Sum,Average等等 • 當需要進階查詢時,例如Distinct,TakeWhile,SkipWhile等等

  44. 漸進式查詢 • 查詢式何時執行? • 當程式嘗試取出元素時 • For Each等列舉式,First等函式 • 實作漸進式查詢 • 要點1 使用IEnumerable(Of T)為參數型別 • 要點2 所有Query回傳值皆為IEnumerable(Of T) • 要點3 傳遞前不要進行列舉動作,否則查詢式會先執行,接下來的動作為疊加式查詢,對效能會有影響

  45. LINQ To XML

  46. LINQ To XML的特色 • 更直覺的XML建立語法 • 與LINQ查詢語句結合的XML查詢式 • 更方便的XML文件操作

  47. 建立XML文件 • VB.NET 2008的新XML建立語法 Dim xmlDoc = _ <Customers> <Customer Name="code6421" Age="18"/> <Customer Name="tom" Age="28"/> <Customer Name="david" Age="38"/> </Customers> xmlDoc.Save("C:\Test.xml") Test.xml <?xml version="1.0" encoding="utf-8"?> <Customers> <Customer Name="code6421" Age="18" /> <Customer Name="tom" Age="28" /> <Customer Name="david" Age="38" /> </Customers>

  48. 新增XML Node • 新增Node至尾端 Dim xmlDoc = XDocument.Load("C:\Test.xml") xmlDoc.<Customers>(0).Add(<Customer Name="Hung" Age="16"/>) xmlDoc.Save("C:\Test2.xml") <?xml version="1.0" encoding="utf-8"?> <Customers> <Customer Name="code6421" Age="18" /> <Customer Name="tom" Age="28" /> <Customer Name="david" Age="38" /> <Customer Name="Hung" Age="16" /> </Customers>

  49. 新增XML Node • 新增Node至最前 Dim xmlDoc = XDocument.Load("C:\Test.xml") xmlDoc.<Customers>(0).AddFirst(<Customer Name="Hung" Age="16"/>) xmlDoc.Save("C:\Test2.xml") <?xml version="1.0" encoding="utf-8"?> <Customers> <Customer Name="Hung" Age="16" /> <Customer Name="code6421" Age="18" /> <Customer Name="tom" Age="28" /> <Customer Name="david" Age="38" /> </Customers>

  50. 新增Attribute至既定Node • Add Attribute Dim xmlDoc = XDocument.Load("C:\Test.xml") xmlDoc.<Customers>(0).<Customer>(0).Add(New XAttribute("Tag", "Test")) xmlDoc.Save("C:\Test2.xml") <?xml version="1.0" encoding="utf-8"?> <Customers> <Customer Name="code6421" Age="18" Tag="Test" /> <Customer Name="tom" Age="28" /> <Customer Name="david" Age="38" /> </Customers>

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