LINQ Join操作
連接是指其中有困難的數據源，以跟隨在一個直接的方式相互關係的目標的操作。
運算符
描述
C#查詢表達式語法
VB查詢表達式語法
Join
運算符連接兩個序列匹配鍵的基礎
join … in … on … equals …
From x In …, y In … Where x.a = y.a
GroupJoin
連接兩個序列和組匹配元素
join … in … on … equals … into …
Group Join … In … On …
查詢表達式 - Join操作示例
C#
using System; using System.Collections.Generic; using System.Linq; namespace Operators { class JoinTables { class DepartmentClass { public int DepartmentId { get; set; } public string Name { get; set; } } class EmployeeClass { public int EmployeeId { get; set; } public string EmployeeName { get; set; } public int DepartmentId { get; set; } } static void Main(string[] args) { List <DepartmentClass> departments = new List <DepartmentClass>(); departments.Add(new DepartmentClass { DepartmentId = 1, Name = "Account" }); departments.Add(new DepartmentClass { DepartmentId = 2, Name = "Sales" }); departments.Add(new DepartmentClass { DepartmentId = 3, Name = "Marketing" }); List <EmployeeClass> employees = new List <EmployeeClass>(); employees.Add(new EmployeeClass { DepartmentId = 1, EmployeeId = 1, EmployeeName = "William" }); employees.Add(new EmployeeClass { DepartmentId = 2, EmployeeId = 2, EmployeeName = "Miley" }); employees.Add(new EmployeeClass { DepartmentId = 1, EmployeeId = 3, EmployeeName = "Benjamin" }); var list = (from e in employees
join d in departments on e.DepartmentId equals d.DepartmentId select new { EmployeeName = e.EmployeeName, DepartmentName = d.Name }); foreach (var e in list) { Console.WriteLine("Employee Name = {0} , Department Name = {1}", e.EmployeeName, e.DepartmentName); } Console.WriteLine("\nPress any key to continue."); Console.ReadKey(); } } }
VB
Module Module1 Sub Main() Dim account As New Department With {.Name = "Account", .DepartmentId = 1} Dim sales As New Department With {.Name = "Sales", .DepartmentId = 2} Dim marketing As New Department With {.Name = "Marketing", .DepartmentId = 3} Dim departments As New System.Collections.Generic.List(Of Department)(New Department() {account, sales, marketing}) Dim william As New Employee With {.EmployeeName = "William", .EmployeeId = 1, .DepartmentId = 1} Dim miley As New Employee With {.EmployeeName = "Miley", .EmployeeId = 2, .DepartmentId = 2} Dim benjamin As New Employee With {.EmployeeName = "Benjamin", .EmployeeId = 3, .DepartmentId = 1} Dim employees As New System.Collections.Generic.List(Of Employee)(New Employee() {william, miley, benjamin}) Dim list = (From e In employees Join d In departments On e.DepartmentId Equals d.DepartmentId Select New Person With {.EmployeeName = e.EmployeeName, .DepartmentName = d.Name}) For Each e In list Console.WriteLine("Employee Name = {0} , Department Name = {1}", e.EmployeeName, e.DepartmentName) Next Console.WriteLine(vbLf &"Press any key to continue.") Console.ReadKey() End Sub Class Employee Public Property EmployeeId As Integer Public Property EmployeeName As String Public Property DepartmentId As Integer End Class Class Department Public Property Name As String Public Property DepartmentId As Integer End Class Class Person Public Property EmployeeName As String Public Property DepartmentName As String End Class End Module
當C#或VB的上述代碼被編譯和執行時，它產生了以下結果：
Emplyee Name = William, Department Name = Account
Emplyee Name = Miley, Department Name = Sales
Emplyee Name = Benjamin, Department Name = Account
Press any key to continue.