fourth-edition | 4th edition of Head First C | Data Visualization library

I'm doing exercises from The Little Schemer, but I do them in Racket using DrRacket.

One of the exercises has two methods referencing each other. Can this be done in Racket and if so, how?

When trying to do it in DrRacket ide I get an error because the one created higher up in the file can't reference something that comes after. I'm assuming this is because it's being interpreted, but I'm not sure.

Is there a way around this issue?

I'm following along in the book C# 8.0 and .NET Core 3.0 - Modern Cross-Platform Development

I'm currently in Chapter 15 on exercise 15.2 where we are tasked with creating a Razor Page that produces a list of customers grouped by country. When you click on a customer name, it takes you to a new page showing the full contact details of that customer and a list of their orders.

Basically there was no exercise or demo in the book that showed us/dealt with page routing.

I'm on the part where I need to display a new page showing the full contact details of the customer clicked on.

In the customers.cshtml page I have asp-page="./CustomerDetails" asp-route-id="@customer.CustomerID" to capture who they are clicking on. Where I am stuck is how do I translate that information into my new page CustomerDetails.cshtml so that the Customer they click on is populated?

It may not be a routing issue, but since I'm new it's my best guess...

I've tried adding a custom routing constraint @page "{CustomerID}" at the top but that just returns the page since I'm guessing the ID value did not get passed in?

CustomerDetails.cshtml

I'm following along in the book C# 8.0and .NET Core 3.0 - Modern Cross-Platform Development

I'm currently in Chapter 15 on exercise 15.2 where we are tasked with creating a Razor Page that produces a list of customers grouped by country. When you click on a customer name, it takes you to a new page showing the full contact details of that customer and a list of their orders.

Taking baby steps, I have built a page that has a card that will have the header as the country and then list each customer name on the card. However, my foreach loop is spitting out each data column under Customer.Country. So if there are 11 countries with Germany, it makes 11 cards with Germany as the title (see image).

It is also populating all of the customer's names as well under each country.

I found that I can use GroupBy() but as I explain below, that causes an invalid cast exception.

customers.cshtml