luggage-tracker-as

Luggage Tracker Demo Smart Contract for LNC Certified Developer

This smart contract for the NEAR protocol uses the hypothetical example of luggage tracking for an airline passenger.

• Passenger can check in their bag, using a unique luggage tag id, their origin and destination.
• The luggage gets status updates along the way (ie. checked in, en-route, ready and collected
• Passenger can check-out their bag, using the bag's code and against their wallet account id

The luggage tracker use-case was chosen in order to study and demonstrate the following:

• Create and push records using persistent storage on the NEAR blockchain
• Delete a record off the storage
• Get and return a record
• Update a record

It also demonstrates a few other common functions, executed on the NEAR VM

• Obtaining a timestamp
• Generating a random string (this function ended up not being used but kept as an example)

Usage

Check-in Luggage

Check-in a luggage item. This call requires a unique id (luggage tag etc), the flight number, the origin airport code, and destination airport code

near call dev-1652560975710-68441058074270 checkInLuggageItem '{"id":"my_bag_id", "flightno":"QF1234", "origin":"SYD", "destination":"JFK"}' --accountId=<your testnet account>

View a luggage item by ID

near view dev-1652560975710-68441058074270 getLuggageItem '{"id":"my-bag-id"}' --accountId=<your testnet account>

Output

{
  id: 'my-bag-id',
  flightno: 'QF1234',
  origin: 'SYD',
  destination: 'JFK',
  ownerAccountId: 'happyrobot.testnet',
  checkInTime: '1653564925754225535',
  checkOutTime: '0',
  status: 'checked-in',
  collectionPoint: null
}

Updates

Update the luggage to 'en-route'
near call dev-1652560975710-68441058074270 enRoute '{"id":"my-bag-id"}' --accountId=<your testnet account>

Update the luggage to "ready" - signifying that the luggage can now be collected.  This call accepts the collectionPoint parameter eg "Carousel 9", "Gate 2" etc etc
near call dev-1652560975710-68441058074270 readyForCollection '{"id":"my-bag-id", "collectionPoint":"Carousel 3"}' --accountId=<your testnet account>

Called when passenger has collected their luggage.
near call dev-1652560975710-68441058074270 collectLuggage '{"id":"my-bag-id"}' --accountId=<your testnet account>

Challenges, Errors and Items of Interest

I’ve added a few challenging errors I encountered, possibly helpful to those learning assembly script on NEAR VM

Nullable Types

When “getting” a PersistantUnoderedMap value, I was getting an error message.
In the example below, I wish to update the class LuggageItem. It would return an error because luggageRecords.get(id) returns a “nullable” type.

Original source:

export function luggageEnRoute(id: string): void {
  let bag: LuggageItem = luggageRecords.get(id)
  bag.enRoute()
  luggageRecords.set(id, bag)
}

The above would give the following error:

ERROR TS2322: Type 'assembly/model/LuggageItem | null' is not assignable to type 'assembly/model/LuggageItem'.

   let bag: LuggageItem = luggageRecords.get(id);

The solution was to cast ‘LuggageItem’ as below:

let bag: LuggageItem = <LuggageItem>luggageRecords.get(id)

Updated function

export function luggageEnRoute(id: string): void {
  let bag: LuggageItem =< LuggageItem> luggageRecords.get(id)
  bag.enRoute()
  luggageRecords.set(id, bag)
}

Timestamps

There is no Date.now() or equivilent. This link provides a much better explanation on obtaining the timestamp using assemblyscript on Near VM - https://dev.to/melvinmanni/common-mistakes-you-might-make-using-the-near-sdk-as-and-assemblyscript-264c

import { context } from "near-sdk-as";


let timestampInNanoseconds = context.blockTimestamp;

Generate a Random String

I didn't end up using this, but an example of the code to generate a random string on Near VM is below.

/*
* Generate a 24 character long random string. 
*/
function generateRandomString(): string {
  let buf = math.randomBuffer(24);
  let b64 = base64.encode(buf);
  return b64;
}