When will you use this?

You use this in every web page and form you build from your first app to production.

• Product pages, login forms, and admin dashboards all use controllers, views, and models.
• When a user submits an order form, model binding maps form fields to a C# class.

Real-world: HDFC-style net banking API

The Banking team building HDFC-style net banking API uses Models and ViewModels to separate database Product from ProductEditViewModel shown on the form. account holders never see the C# code — they just get a fast, reliable transfer endpoints and account balance.

Production-style code

// Entity
public class Product
{
    public int Id { get; set; }
    public string Name { get; set; } = "";
    public decimal CostPrice { get; set; }  // admin only
    public decimal SalePrice { get; set; }
}

// ViewModel for storefront
public class ProductCardVm
{
    public string Name { get; set; } = "";
    public decimal SalePrice { get; set; }
}

What happens in production: In HDFC-style net banking API, getting Models and ViewModels right means account holders trust the transfer endpoints and account balance every day.

Lesson example (start here)

Copy this smaller example first. Once it works, compare it with the real-world code above.

// Entity
public class Product
{
    public int Id { get; set; }
    public string Name { get; set; } = "";
    public decimal CostPrice { get; set; }  // admin only
    public decimal SalePrice { get; set; }
}

// ViewModel for storefront
public class ProductCardVm
{
    public string Name { get; set; } = "";
    public decimal SalePrice { get; set; }
}

Line-by-line walkthrough

How it works (big picture)

• The view only gets Name and SalePrice — not CostPrice.
• Map from Product to ProductCardVm in the controller or a service.

Do this on your computer

1. Create a Product class and a ProductEditVm with only form fields.
2. Build a create form bound to ProductEditVm.
3. Map to Product before saving to the database.
4. Read the real-world section and name which part of the app uses this topic.
5. Run the example locally with dotnet run and confirm the same behavior.
6. Change one value in the example (route, text, or connection string) and predict what will happen before you save.

Experiments — try changing this

• Change a string or route in the example and save — watch the browser or Swagger response update.
• Break the code on purpose (remove a semicolon), read the error message, then fix it.

Remember

Model = domain/data shape. ViewModel = what one view needs. Do not expose internal fields to the browser.

Common questions