#1321 Updated readme and add UML diagram

transaction-script/Readme.md

@@ -11,33 +11,110 @@ tags:
 ## Intent
 Transaction script(TS) is mainly used in small applications where nothing complex is done and bigger architecture's are not needed.
 
-## Name / classification
-...
+## Explanation
+Real world example
+> Your need is to be able to book a hotel room and also be able to cancel that booking.
+> 
 
-## Also known as
-...
+In plain words
+> All logic related to booking a hotel room like checking room availability,
+> calculate rates and update the database is done inside a single transaction script.
+> Similar procedure is also needed for cancelling a room booking and all 
+> that logic will be in another transaction script.
 
+Programmatic example
 
-## Explanation
-...
+The Hotel class takes care of booking and cancelling a room in a hotel.
+
+```java
+public class Hotel {
+  private static final Logger LOGGER = LoggerFactory.getLogger(TransactionScriptApp.class);
+
+  private HotelDaoImpl hotelDao;
+
+  public Hotel(HotelDaoImpl hotelDao) {
+    this.hotelDao = hotelDao;
+  }
+
+  public void bookRoom(int roomNumber) throws Exception {
+
+    Optional<Room> room = hotelDao.getById(roomNumber);
+
+    if (room.isEmpty()) {
+      throw new Exception("Room number: " + roomNumber + " does not exist");
+    } else {
+      if (room.get().isBooked()) {
+        throw new Exception("Room already booked!");
+      } else {
+        Room updateRoomBooking = room.get();
+        updateRoomBooking.setBooked(true);
+        hotelDao.update(updateRoomBooking);
+      }
+    }
+  }
+
+  public void cancelRoomBooking(int roomNumber) throws Exception {
+
+    Optional<Room> room = hotelDao.getById(roomNumber);
+
+    if (room.isEmpty()) {
+      throw new Exception("Room number: " + roomNumber + " does not exist");
+    } else {
+      if (room.get().isBooked()) {
+        Room updateRoomBooking = room.get();
+        updateRoomBooking.setBooked(false);
+        int refundAmount = updateRoomBooking.getPrice();
+        hotelDao.update(updateRoomBooking);
+
+        LOGGER.info("Booking cancelled for room number: " + roomNumber);
+        LOGGER.info(refundAmount + " is refunded");
+      } else {
+        throw new Exception("No booking for the room exists");
+      }
+    }
+  }
+}
+```
+
+This class has two methods, one for booking and cancelling a room respectively.
+
+```
+public void bookRoom(int roomNumber);
+```
+The book room method consolidates all the needed steps like checking if the room is already booked
+or not, if not booked then books the rooma nd updates the database by using the DAO. 
+
+```
+public void cancelRoomBooking(int roomNumber)
+```
+The cancel room method consolidates steps like checking if the room is booked or not, 
+if booked then calculates the refund amount and updates the database using the DAO.
 
 ## Class diagram
-...
+![alt text](./etc/transaction-script.png "Transaction script model")
 
 ## Applicability
-...
+Use the transaction script model when the application has only a small amount of logic and that
+logic won't be extended in the future.
 
-## Tutorials
-...
 
 ## Known uses
-...
+* Revenue recognition in business systems.
 
-## Consequences (the good and the bad, add criticism here)
-...
+## Consequences
+* As the business logic gets more complicated, 
+it gets progressively harder to keep the transaction script 
+in a well-designed state.
+* Code duplication between transaction scripts can occur.
+* Normally not easy to refactor transactions script to other domain logic
+patterns.
 
 ## Related patterns
-...
+* Domain Model
+* Table Module
+* Service Layer
 
 ## Credits
-...
+* [Transaction Script Pattern](https://dzone.com/articles/transaction-script-pattern#:~:text=Transaction%20Script%20(TS)%20is%20the,need%20big%20architecture%20behind%20them.)
+* [Transaction Script](https://www.informit.com/articles/article.aspx?p=1398617)
+* [Patterns of Enterprise Application Architecture](https://www.amazon.com/gp/product/0321127420?ie=UTF8&tag=gupesasnebl-20&linkCode=as2&camp=1789&creative=9325&creativeASIN=0321127420)