Generic constraints (where clause) in C Sharp (C#) - Mini Project: Build & Apply

Filtering Products with Generic Constraints in C#

📖 Scenario: You work in a store that sells different products. You want to keep a list of products and filter them based on their price.

🎯 Goal: Create a generic class that can filter products by price using a generic constraint with a where clause.

📋 What You'll Learn

Create a class Product with properties Name (string) and Price (decimal).

Create a generic class Filter<T> with a where clause that restricts T to be Product or a subclass.

Add a method FilterByPrice in Filter<T> that returns products with price less than a given value.

Create a list of Product objects with exact values.

Use the FilterByPrice method to get products cheaper than a specific price and print their names.

💡 Why This Matters

🌍 Real World

Stores and e-commerce platforms often filter products by price or other attributes. Using generic constraints helps create reusable filtering classes.

💼 Career

Understanding generic constraints and filtering data is important for software developers working with collections, databases, and APIs.

1

Create the Product class and product list

Create a class called Product with two public properties: Name of type string and Price of type decimal. Then create a list called products with these exact entries: new Product { Name = "Pen", Price = 1.5m }, new Product { Name = "Notebook", Price = 3.0m }, new Product { Name = "Backpack", Price = 25.0m }.

C Sharp (C#)

// Your code here

Need a hint?

Define the Product class with two properties. Then create a List<Product> with the exact products.

2

Add generic Filter class with where constraint

Create a generic class called Filter<T> with a where clause that restricts T to be Product or a subclass. Inside it, add a public field items of type List<T>.

C Sharp (C#)

using System;
using System.Collections.Generic;

public class Product
{
    public string Name { get; set; }
    public decimal Price { get; set; }
}

public class Filter where T : Product
{
    public List items;
    // Your code here
}

class Program
{
    static void Main()
    {
        List products = new List
        {
            new Product { Name = "Pen", Price = 1.5m },
            new Product { Name = "Notebook", Price = 3.0m },
            new Product { Name = "Backpack", Price = 25.0m }
        };
    }
}

Need a hint?

Use where T : Product to restrict the generic type. Add a constructor to set the items field.

3

Add FilterByPrice method to Filter class

Inside the Filter<T> class, add a method called FilterByPrice that takes a decimal maxPrice parameter and returns a List<T> of items with Price less than maxPrice. Use LINQ Where to filter.

C Sharp (C#)

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

public class Product
{
    public string Name { get; set; }
    public decimal Price { get; set; }
}

public class Filter where T : Product
{
    public List items;

    public Filter(List items)
    {
        this.items = items;
    }

    // Add FilterByPrice method here
}

class Program
{
    static void Main()
    {
        List products = new List
        {
            new Product { Name = "Pen", Price = 1.5m },
            new Product { Name = "Notebook", Price = 3.0m },
            new Product { Name = "Backpack", Price = 25.0m }
        };
    }
}

Need a hint?

Use LINQ Where to select items with price less than maxPrice.

4

Use Filter class and print filtered product names

In the Main method, create an instance of Filter<Product> called filter using the products list. Then call FilterByPrice with 5.0m and store the result in cheapProducts. Finally, print the Name of each product in cheapProducts on separate lines.

C Sharp (C#)

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

public class Product
{
    public string Name { get; set; }
    public decimal Price { get; set; }
}

public class Filter where T : Product
{
    public List items;

    public Filter(List items)
    {
        this.items = items;
    }

    public List FilterByPrice(decimal maxPrice)
    {
        return items.Where(item => item.Price  products = new List
        {
            new Product { Name = "Pen", Price = 1.5m },
            new Product { Name = "Notebook", Price = 3.0m },
            new Product { Name = "Backpack", Price = 25.0m }
        };

        // Your code here
    }
}

Need a hint?

Create the Filter<Product> instance and call FilterByPrice(5.0m). Print each product's Name from the result.