Add detailed comments explaining controller and model functionality in slides

Author: dasunpubudumal

presentation/slides.md

@@ -277,6 +277,25 @@ async fn route(
 ```
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+<!-- 
+Our controller is simple - a single function responsible for handling the incoming HTTP requests and dispatching the request to the handler using the route function.
+
+It takes a request and a database connection pool. It returns a response with a body of bytes or an error.
+If we don’t recognise the request, we return a bad request response.
+
+➡️ ➡️ ➡️ 
+
+The route function dispatches the request: it receives incoming HTTP requests and decides which service should handle them.
+
+
+Requests are matched based on method + URI path:
+OPTIONS → handled by preflight() (CORS).
+POST /scan → forwarded to the scan service.
+POST /searches → forwarded to the search service.
+Any other request → returns 404 Not Found.
+So, the controller separates request handling from business logic, forwarding requests to services without performing the business logic itself.
+-->
+
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@@ -339,6 +358,20 @@ transition: fade-out
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+<!-- 
+These are the models to access the database.
+
+They are Rust structs and they have implemented functions.
+
+They match the CRUD pattern, create, read, update and delete. We do not have deletions.
+
+Taking create as an example: It takes barcode String, unsigned 32 bit location id, and connection pool. It returns a Result of either Labware or a LabwareError. This is a common pattern in Rust. Using Result allows the caller to handle success and failure explicitly.
+
+As you see we have unit tests for each function we have implemented.
+
+This concludes the overall architecture and a little introduction to code.
+-->
+
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