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Module 3: Routing in ASP.NET Core MVC


3.1. Understanding Routing Fundamentals

3.1.1. What is Routing?
Definition
Routing maps URLs to action methods.
Routing in MVC
How routing enables friendly URLs.

3.1.2. Routing Configuration
Default Route
{controller=Home}/{action=Index}/{id?}.
Setting Up Routes
Configuring routes in Program.cs using endpoints.MapControllerRoute.

3.1.3. Route Parameters
Mandatory and Optional Parameters
{id} vs. {id?}.
Route Constraints
Enforcing parameter types ({id:int}).

3.1.4. Route Templates
Creating Custom Routes
Defining specific URL patterns.
Multiple Routes
Adding multiple routes to support different URL structures.
Hands-On Exercises
Exercise 1: Modify the default route to change the default controller and action.
Exercise 2: Create a custom route for products, such as products/details/{id}.


3.2. Conventional Routing

3.2.1. Defining Conventional Routes
Multiple Route Definitions
Adding routes with different patterns.
Route Order
Understanding how the order affects route matching.

3.2.2. Route Constraints and Defaults
Applying Constraints
Using constraints like {id:int}, {slug:alpha}.
Setting Defaults
Providing default values for parameters.

3.2.3. Route Names
Naming Routes
Assigning names to routes for URL generation.
Using Route Names in Links
Generating URLs with Url.RouteUrl("RouteName").
Hands-On Exercises
Exercise 1: Create a route with constraints that only matches numeric IDs.
Exercise 2: Name a route and use it to generate a URL in a view.


3.3. Attribute Routing

3.3.1. Introduction to Attribute Routing
Defining Routes with Attributes
Using [Route] on controllers and actions.
Advantages of Attribute Routing
Closer to action methods, easier to manage.

3.3.2. Route Prefixes
Applying Route Prefixes
Using [Route("products")] on a controller.
Combining Prefixes and Routes
How controller and action routes are combined.

3.3.3. HTTP Verb Attributes
Restricting Actions to HTTP Methods
[HttpGet], [HttpPost].
Route Templates with HTTP Verbs
[HttpPost("create")].

3.3.4. Route Parameters and Constraints
Defining Parameters
[Route("{id}")].
Applying Constraints
[Route("{id:int}")].

3.3.5. Optional Parameters
Defining Optional Parameters
[Route("{id?}")].
Default Values
[Route("details/{id=1}")].
Hands-On Exercises
Exercise 1: Implement attribute routing for the ProductController.
Exercise 2: Use HTTP verb attributes to create separate actions for GET and POST requests.


3.4. Advanced Routing Techniques

3.4.1. Areas
What are Areas?
Organizing large applications into sections.
Creating an Area
Adding an Areas folder and area-specific controllers and views.
Configuring Area Routes
Using [Area("Admin")] attribute.
Linking to Actions in Areas
Specifying the area in URLs and links.

3.4.2. Custom Route Constraints
Implementing IRouteConstraint
Creating custom logic for route matching.
Using Custom Constraints
Applying the constraint in route definitions.

3.4.3. Ignoring Routes
Excluding Routes
Ignoring specific URL patterns (e.g., {resource}.axd/{*pathInfo}).

3.4.4. Route Priority and Precedence
Understanding Route Matching
How the routing engine selects a route.
Resolving Conflicts
Ensuring specific routes are matched before general ones.
Hands-On Exercises
Exercise 1: Create an Admin area and set up its routing.
Exercise 2: Implement a custom route constraint that only allows alphanumeric slugs.


3.5. Generating URLs and Links

3.5.1. URL Generation in Controllers
Using Url Helper Methods
Url.Action, Url.RouteUrl.
Generating Absolute URLs
Providing full URLs for emails or redirects.

3.5.2. URL Generation in Views
Using Html Helper Methods
Html.ActionLink, Html.RouteLink.
Passing Route Values
Specifying parameters in links.
Hands-On Exercise
Exercise: Create navigation links in your layout that dynamically generate URLs based on routes.