LINQ 物件

LINQ to Objects 允許使用任何支援 IEnumerable<T> 的 LINQ 查詢，以訪問記憶體中的資料集合，而無需使用 LINQ 供應商 (API)，就像 LINQ to SQL 或 LINQ to XML 中的情況。

LINQ to Objects 簡介

LINQ to Objects 中的查詢通常只返回型別為 IEnumerable<T> 的變數。簡而言之，LINQ to Objects 為集合提供了一種新的方法，因為以前，必須編寫冗長的編碼（高複雜度的 foreach 迴圈）才能從集合中檢索資料，而現在則改用編寫描述該所需檢索資料的宣告性程式碼。

LINQ to Objects 相較於傳統的 foreach 迴圈有許多優勢，如更強的可讀性、強大的篩選、分組能力、最少的應用程式編碼即可增強排序。此類 LINQ 查詢本質上也更緊湊，並且可以移植到任何其他資料來源，而無需修改或只需進行少量修改。

下面是一個簡單的 LINQ to Objects 示例 −

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace LINQtoObjects {
   class Program {
      static void Main(string[] args) {
      
         string[] tools = { "Tablesaw", "Bandsaw", "Planer", "Jointer", "Drill", "Sander" };
         var list = from t in tools select t;

         StringBuilder sb = new StringBuilder();

         foreach (string s in list) {
            sb.Append(s + Environment.NewLine);
         }
		 
         Console.WriteLine(sb.ToString(), "Tools");
         Console.ReadLine();
      }
   }
}

在該示例中，字串陣列 (tools) 用作要使用 LINQ to Objects 查詢的物件集合。

Objects query is:
var list = from t in tools select t;

當編譯並執行上述程式碼時，會生成以下結果 −

Tablesaw
Bandsaw
Planer
Jointer
Drill
Sander

使用 LINQ to Objects 查詢記憶體中的集合

C#

using System;
using System.Collections.Generic;
using System.Linq;

namespace LINQtoObjects {
   class Department {
      public int DepartmentId { get; set; }
      public string Name { get; set; }
   }

   class LinqToObjects {
      static void Main(string[] args) {
      
         List<Department> departments = new List<Department>();
			
         departments.Add(new Department { DepartmentId = 1, Name = "Account" });
         departments.Add(new Department { DepartmentId = 2, Name = "Sales" });
         departments.Add(new Department { DepartmentId = 3, Name = "Marketing" });

         var departmentList = from d in departments
                              select d;

         foreach (var dept in departmentList) {
            Console.WriteLine("Department Id = {0} , Department Name = {1}",
               dept.DepartmentId, dept.Name);
         }
		 
         Console.WriteLine("\nPress any key to continue.");
         Console.ReadKey();
      }
   }
}

VB

Imports System.Collections.Generic
Imports System.Linq

Module Module1

   Sub Main(ByVal args As String())

      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 departmentList = From d In departments

      For Each dept In departmentList
         Console.WriteLine("Department Id = {0} , Department Name = {1}", dept.DepartmentId, dept.Name)
      Next

      Console.WriteLine(vbLf & "Press any key to continue.")
      Console.ReadKey()
   End Sub

   Class Department
      Public Property Name As String
      Public Property DepartmentId As Integer
   End Class
   
End Module

當編譯並執行上述 C# 或 VB 程式碼時，會生成以下結果 −

Department Id = 1, Department Name = Account
Department Id = 2, Department Name = Sales
Department Id = 3, Department Name = Marketing

Press any key to continue.