Dev 221 VBLINQ Language Integrated Query LINQ VB

Dev 221 VB中的LINQ: 未来之路

Language Integrated Query

LINQ项目 VB C# Others… . NET Language Integrated Query Standard Query Operators DLinq (ADO. NET) XLinq (System. XML) <book> <title/> <author/> <year/> <price/> </book> Objects SQL XML

语言的创新点 Implicitly typed locals 隐式类型的局部变量 Extension methods Extension方法 Dim x = 5 <Extension> Sub Randomize(col As Collection) Function(c) c. Name Inline functions 内联函数 New Point { x : = 1, y : = 2 } Object initializers 对象初始值 New { c. Name, c. Phone } Anonymous types 匿名类型 Query expressions 查询表达式 From … Where … Select

查询语法 Project Select <expr> Filter Where <expr> Test Any(<expr>), All(<expr>) Join <expr> On <expr> Group By <expr> Aggregate Count(<expr>), Sum(<expr>), Min(<expr>), Max(<expr>), Avg(<expr>) Partition Top <expr> Set Distinct, Union, Intersect, Except Order By <expr> Convert To. Array, To. List, To. Binding. List Cast As <typename>, Of. Type(Of T)

关系型数据的DLinq 当前访问数据的方法 Sql. Connection c = new Sql. Connection(…); Queries in c. Open(); quotes Sql. Command cmd = new Sql. Command( @"SELECT c. Name, c. Phone FROM Customers c Loosely bound WHERE c. City = @p 0"); arguments cmd. Parameters["@p 0"] = "London"; Data. Reader dr = c. Execute(cmd); while (dr. Read()) { Loosely typed string name = r. Get. String(0); result sets string phone = r. Get. String(1); Date. Time date = r. Get. Date. Time(2); } r. Close(); No compile time checks

关系型数据的DLinq 使用DLing访问数据 Public Class Customer … Classes describe data Public Class Northwind Inherits Data. Context Tables are like collections Public Property Customers As Table(Of Customer) … Strongly typed End Class connection Dim db As New Northwind(…) Dim contacts = _ Integrated From c in db. Customers _ query syntax Where c. City = "London" Select c. Name, c. Phone Strongly typed results

XML数据的XLinq 当前XML编程方式 Imperative model Dim doc As New Xml. Document() Dim contacts As XMLElement = doc. Create. Element("contacts") Document For Each Dim c in Customers centric If (c. Country = "USA") Dim e As XMLElement = doc. Create. Element("contact") Dim name As XMLElement = doc. Create. Element("name")No integrated queries name. Inner. Text = c. Company. Name e. Append. Child(name) Dim phone As XMLElement = doc. Create. Element("phone") Memory phone. Inner. Text = c. Phone intensive e. Append. Child(phone) <contacts> <contact> contacts. Append. Child(e) <name>Great Lakes Food</name> End If <phone>(503) 555 -7123</phone> Next </contact> … doc. Append. Child(contacts) </contacts>

XML数据的XLinq 使用XLinq进行编程 Dim contacts As New XElement("contacts", _ From c in customers _ Where c. Country = "USA“ _ Select New XElement("contact", _ new XElement("name", c. Company. Name), _ new XElement("phone", c. Phone) _ ) ) Declarative model Element centric Integrated queries Smaller and faster

在Visual Basic中集成XML 利用XLinq在VB中进行XML编程 Infers XLinq XElement Dim contacts = _ <contacts> No conceptual <%= _ barrier From c In customers _ Where c. Country = "USA" _ Select <contact> <name> <%= c. Company. Name %></name> <phone> <%= c. Phone %></phone> </contact> _ %> </contacts> Expression holes for computed values

使用XLinq

总结 § Language Integrated Query Language 的优点 § 对于对象数据, 关系型数据和XML数据的统一查询 § 查询的类型 § 在VB和C#中的类似SQL和XQuery的查询 § 仅支持. NET平台 § 更多信息 § 主页: http: //msdn. microsoft. com/netframework/future/linq/ § 可下载Customer Tech Previews版本! § Contact: Juliapa@microsoft. com 我们需要您的反馈意见

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XML Member Binding XML成员绑定 Late binding covers all XML axes 延后绑定所有的 XML axes Dim cosmos As XElement = Get. Current. Link. Cosmos(). Root Dim ver As Double = CDbl(cosmos. Attribute("version")) Dim item As XElement = First(cosmos. Descendents("item")) Dim created As Date = CDate(item. Element("linkcreated“)) Attributes Descendents Dim cosmos As XElement = Get. Current. Link. Cosmos(). Root Elements Dim ver As Double = CDbl(cosmos. @version) Dim item As XElement = cosmos…<item>. Value Dim created As Date = CDate(item. <linkcreated>)

XML Literals Shorthand for object creation 编写对象生成代码 Dim emp = _ <employee> <name>Joe</name> <age>28</age> <department id="432"> <deptname>Engineering</deptname> </department> </employee> Dim emp = _ New XElement("employee", _ New XElement("name", "Joe"), _ New XElement("age", 28), _ New XElement("department", _ New XElement("name", "Engineering"), _ New XAttribute("id", 432)))

Deferred Query Execution 向后优先解析的查询表达式 Dim custs() As Customer = Sample. Data. Get. Customers() Dim q = Select c. City From c In custs Where c. State = "WA" Dim q = custs. Where(Address. Of _Filter 1). Select(Address. Of _Project 1) Dim names() As String = q. To. Array() custs ID names Name Phone Where Address. Of _Filter 1 Select Address. Of _Project 1

Expression Trees 表达式树 Defer code interpretation System. Query. Expression(Of T) where T is a delegate type 向后优先解析的代码 Dim f As Predicate(Of Customer) = (c) c. State = "CA" Dim e As Expression(Of Predicate(Of Customer)) = _ New Expression(Of Predicate(Of Customer))( New Binary. Expression(Expression. Type. EQ, New Property. Expression( New Parameter. Expression(0), Get. Type(Customer). Get. Property("State") ), New Constant. Expression("CA") ) )

Extension Methods 扩展模型 Extend existing types with new methods 使用新方法扩展存在的类型 Extension Int. Arr. Extensions To Integer() Function Sort() As Integer() … End Function Read. Only Property Sum() As Integer obj. Foo(x, y) Get Imports Integer. Arr. Extensions … XXX. Foo(obj, x, y) End Get Dim values() As Integer = Get. Values() End Property Console. Write. Line(Integer. Arr. Extensions. Sum(Integer. Extensions. Sort(values)) End Extension Dim values() As Integer = Get. Values() Console. Write. Line(values. Sort(). Sum())

Simple Type Inference 简单类型引用 Variable type inferred from initializer 由初始值推断的变量类型 Integer String Double All types are Object! Dim x = 5 Dim s = "Hello" Dim d = 1. 0 Dim numbers = New Integer() {1, 2, 3} Dim orders = new Dictionary(Of Integer, Order)()

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