LINQ - Objects

LINQ to Objects offers usage of any LINQ query supporting IEnumerable<T>for accessing in-memory data collections without any need of LINQ provider (API) as in case of LINQ to SQL or LINQ to XML.

Introduction of LINQ to Objects

Queries in LINQ to Objects return variables of type usually IEnumerable<T> only. In short, LINQ to Objects offers a fresh approach to collections as earlier, it was vital to write long coding (foreach loops of much complexity) for retrieval of data from a collection which is now replaced by writing declarative code which clearly describes the desired data that is required to retrieve.

There are also many advantages of LINQ to Objects over traditional foreach loops like more readability, powerful filtering, capability of grouping, enhanced ordering with minimal application coding. Such LINQ queries are also more compact in nature and are portable to any other data sources without any modification or with just a little modification.

Below is a simple LINQ to Objects example −

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();
      }
   }
}

In the example, an array of strings (tools) is used as the collection of objects to be queried using LINQ to Objects.

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

When the above code is compiled and executed, it produces the following result −

Tablesaw
Bandsaw
Planer
Jointer
Drill
Sander

Querying in Memory Collections Using LINQ to Objects

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

When the above code of C# or VB is compiled and executed, it produces the following result −

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

Press any key to continue.