Events

Events are emitted during the execution of a transaction. Each Move module can define its own events and choose when to emit the events upon execution of the module. For example, during a coin transfer, both the sender and receiver's accounts will emit SentEvent and ReceivedEvent, respectively. This data is stored within the ledger and can be queried via the REST interface's Get events by event handle.

Assuming that an account 0xc40f1c9b9fdc204cf77f68c9bb7029b0abbe8ad9e5561f7794964076a4fbdcfd had sent coins to another account, the following query could be made to the REST interface: https://fullnode.devnet.aptoslabs.com/v1/accounts/c40f1c9b9fdc204cf77f68c9bb7029b0abbe8ad9e5561f7794964076a4fbdcfd/events/0x1::coin::CoinStore<0x1::aptos_coin::AptosCoin>/withdraw_events. The output would be all WithdrawEvents stored on that account, it would look like

[{
  "key":"0x0000000000000000caa60eb4a01756955ab9b2d1caca52ed",
  "sequence_number":"0",
  "type":"0x1::coin::WithdrawEvent",
  "data":{
    "amount":"1000"
  }
}]

Each registered event has a unique key. The key 0x0000000000000000c40f1c9b9fdc204cf77f68c9bb7029b0abbe8ad9e5561f7794964076a4fbdcfd maps to the event 0x1::coin::CoinStore<0x1::aptos_coin::AptosCoin>/sent_events registered on account 0xc40f1c9b9fdc204cf77f68c9bb7029b0abbe8ad9e5561f7794964076a4fbdcfd. This key can then be used to directly make event queries, e.g., https://fullnode.devnet.aptoslabs.com/v1/events/0000000000000000c40f1c9b9fdc204cf77f68c9bb7029b0abbe8ad9e5561f7794964076a4fbdcfd.

These represent event streams, or a list of events with each entry containing a sequentially increasing sequence_number beginning at 0, a type, and data. Each event must be defined by some type. There may be multiple events defined by the same or similar types especially when using generics. Events have associated data. The general principle is to include all data necessary to understand the changes to the underlying resources before and after the execution of the transaction that changed the data and emitted the event.