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Sessions/Session02/Notes/02_Notes.md

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+## **7. Model Validation**
+
+ASP.NET Core MVC provides model validation, which helps ensure that data received from the user is valid.
+
+### Example: Data Annotations
+
+
+
+```c#
+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
+
+---
+
+## **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
+
+
+```c#
+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:
+
+
+```c#
+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:
+
+```c#
+@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.
+
+---
+
+## **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.
+    
+    
+```c#
+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.
+    
+
+---
+
+
+
+
+What is Business Logic