C# Query Expression is a form of expression crafted using LINQ query syntax. LINQ (Language Integrated Query) serves as a tool to build queries.
C# Query Expression consists of a series of clauses and employs a syntax that resembles SQL queries.
A query expression should commence with a from clause and conclude with a select or group clause.
To retain the query, an IEnumerable type variable must be employed. This variable offers an IEnumerator.MoveNext function for traversing elements.
We have two methods to iterate through elements in the IEnumerable sequence:
- Utilizing the IEnumerator.MoveNext method
- Employing the foreach loop
Note: We must use System.Linq namespace to execute query expression.
Let's examine an example demonstrating how to filter and display odd numbers from an array using the expression query.
C# Query Expression Example 1
using System;
using System.Linq;
using System.Collections.Generic;
namespace CSharpFeatures
{
class DelegateInference
{
static void Main(string[] args)
{
int[] IntVal = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
// Query Expression
IEnumerable<int> OddVal =
from val in IntVal
where (val % 2) != 0
select val;
// Iterating fetched result
foreach (int val in OddVal)
{
Console.WriteLine(val);
}
}
}
}
Output
1
3
5
7
9
C# Query Expression Example 2
In this instance, we are utilizing a query expression to retrieve the student's name from the students' collection.
using System;
using System.Linq;
using System.Collections.Generic;
namespace CSharpFeatures
{
class Student
{
public int ID { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public static List<Student> GetStudents()
{
List<Student> student = new List<Student>();
Student student1 = new Student { ID = 101, Name = "Irfan", Email = "[email protected]"};
Student student2 = new Student { ID = 102, Name = "Rahul", Email = "[email protected]" };
Student student3 = new Student { ID = 103, Name = "John", Email = "[email protected]" };
student.Add(student1);
student.Add(student2);
student.Add(student3);
return student;
}
}
class QueryExpressionExample
{
static void Main(string[] args)
{
IEnumerable<string> queryName =
from student in Student.GetStudents()
where student.ID == 103
select student.Name;
foreach (var s in queryName)
Console.Write(s);
}
}
}
It displays a student, having student id 103.
Output
