Mastering Data Passing & ViewModels (The Professional Journey)

How you pass data from a Controller to a View determines the maintainability of your entire project. Professional .NET developers avoid "Magic Strings" and embrace **Strongly Typed ViewModels**.

Section 1: The "Dynamic" Ways (Weakly Typed)

Section 2: The "Expert" Way — The ViewModel Pattern

A ViewModel is a custom class created specifically for a View. It only contains the data that the View needs to display. This is the **Standard** for any enterprise application.

Why use ViewModels?

• Decoupling: Your View doesn't need to know about your Database Entities (Domain Models).
• Type-Safety: Get IntelliSense and compile-time errors in your Razor code.
• Validation: Use **Data Annotations** directly on the ViewModel properties.

// 1. The ViewModel (The "Contract")
public class UserProfileViewModel {
    public string FullName { get; set; }
    public string Email { get; set; }
    public bool IsAdmin { get; set; }
    public List RecentLogins { get; set; }
}

// 2. The Controller (The "Mapper")
public IActionResult Profile(int id) {
    var user = _db.Users.Find(id); // Domain Model
    
    var viewModel = new UserProfileViewModel {
        FullName = user.FirstName + " " + user.LastName,
        Email = user.Email,
        IsAdmin = user.Role == "Admin",
        RecentLogins = user.Logins.Take(5).ToList()
    };

    return View(viewModel); // Strongly Typed!
}
                

Section 3: State Persistence with TempData

TempData is used to pass data between two consecutive requests (e.g., from Redirect to Action). It uses Session/Cookies internally.

public IActionResult Save() {
    TempData["Success"] = "Product saved successfully!";
    return RedirectToAction("Index"); // Data survives this redirect!
}