Selecting Multiple Columns in LINQ in C#: A Beginner's Guide with Examples

LINQ (Language Integrated Query) in C# simplifies data querying with its expressive syntax. A common requirement is selecting multiple columns from a data source. This article aims to demystify this process through simple and practical examples, making it easy for beginners to grasp.

Basics of Selecting Multiple Columns

In LINQ, the select clause is used to specify the columns or properties you want to retrieve from a data source. When you need multiple columns, LINQ offers several ways to achieve this, which we'll explore through examples.

Example 1: Using Anonymous Types

The most common method is to use anonymous types. This approach lets you create a new object on the fly.

var people = new List<Person> 
{
    new Person { Name = "Alice", Age = 30, City = "London" },
    new Person { Name = "Bob", Age = 25, City = "Paris" }
};

var selectedData = people.Select(person => new { person.Name, person.City });
foreach (var item in selectedData)
{
    Console.WriteLine($"Name: {item.Name}, City: {item.City}");
}

Explanation:

• We have a list of Person objects.
• We use Select to create an anonymous type with Name and City.
• The results contain only the selected properties.

Example 2: Using Tuples

With C# 7.0 and later, you can use tuples for a similar result.

var selectedData = people.Select(person => (person.Name, person.Age));
foreach (var item in selectedData)
{
    Console.WriteLine($"Name: {item.Name}, Age: {item.Age}");
}

Explanation:

• Tuples are used to select Name and Age.
• The result is a collection of tuples with the selected data.

Example 3: Selecting into a New Class

For more complex scenarios or to improve readability, you can define a new class. 

public class PersonInfo
{
    public string Name { get; set; }
    public int Age { get; set; }
}

var selectedData = people.Select(person => new PersonInfo { Name = person.Name, Age = person.Age });
foreach (var personInfo in selectedData)
{
    Console.WriteLine($"Name: {personInfo.Name}, Age: {personInfo.Age}");
}

Explanation:

• A new class PersonInfo is defined.
• We project each Person object into a new PersonInfo object.

Conclusion

Selecting multiple columns in LINQ is a powerful feature that offers flexibility and readability in querying data. Whether using anonymous types, tuples, or projecting into a new class, LINQ provides the tools to efficiently retrieve and manipulate the required data in C#.

Practicing these methods will help solidify your understanding of LINQ and its capabilities in handling complex data selection scenarios.