ASP.NET/Sessions/Session02/Notes/02_Notes.md

7. Model Validation

ASP.NET Core MVC provides model validation, which helps ensure that data received from the user is valid.

Example: Data Annotations

public class Product {
	public int Id { get; set; }
	[Required]
	[StringLength(50)]
	public string Name { get; set; }
	[Range(0, 10000)]
	public decimal Price { get; set; } 
	}

• Required: Ensures the property has a value.
• StringLength: Restricts the maximum length.
• Range: Limits the value to a specified range.

Validation errors are automatically displayed in views if you include @Html.ValidationMessageFor for each property or @Html.ValidationSummary() to show all errors.

Summary

• Models represent data and business logic.
• Properties in models define data structure and encapsulate fields.
• Controller-View Interaction: Pass models to views using View(model);.

Side Notes

catchall in routing

appsettings.json

query parameters

apply the teaching techniques

Razor View Engine

how to optimize the projects code

Talk about lists C#

how to return custom view

assign C# variable and use it

ViewBag.... is a dynamic ViewBag.myName...

hot reload...

what actually is viweBag, viewData

Layouts..

_ViewStart _Shared

_MyLayout cshtml

RenderBody RenderSection (required... )

_ViewImports

HtmlHelper / TagHelper

partial view

How to pass data to partial views

Models and Model Types

1. Binding Models
2. Application Models
3. View Models https://learn.microsoft.com/en-us/aspnet/core/mvc/views/razor?view=aspnetcore-8.0

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5. View Models vs. Domain Models

In some cases, the data needed by a view might be a combination of several models or require custom formatting. A View Model is a class specifically created to supply the view with only the necessary data.

Creating a View Model

public class ProductViewModel 
{ 
	public int Id { get; set; }
	public string Name { get; set; }
	public decimal Price { get; set; }
	public string FormattedPrice => $"${Price:N2}"; 
}

Using a view model keeps the domain model (Product) separate, especially useful when the view requires additional fields or formatting.

Using the View Model in the Controller and View

In the controller:

public IActionResult Details() 
{
	var product = new Product { Id = 1, Name = "Laptop", Price = 1500.00m };
	var productViewModel = new ProductViewModel 
	{ 
		Id = product.Id,
		Name = product.Name,
		Price = product.Price
	};      
	return View(productViewModel); }

In the view:

@model ProductViewModel  <h2>Product Details</h2> <p>Product Name: @Model.Name</p> <p>Price: @Model.FormattedPrice</p>

View models allow you to tailor data specifically for the view, improving separation of concerns and maintainability.

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6. Model Binding in ASP.NET Core MVC

Model binding is a feature in ASP.NET Core that automatically maps HTTP request data to action parameters, making it easier to pass user inputs to models.

• From URL or Query String: If the action expects a model parameter and the URL includes a query string, model binding will automatically populate the model’s properties.

public IActionResult UpdatePrice(int id, decimal price) {     // id and price are bound from the query string or route data }

• From Form Data: For form submissions, model binding maps form inputs to model properties by matching the names.

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What is Business Logic