Ethereum Stack Exchange is a question and answer site for users of Ethereum, the decentralized application platform and smart contract enabled blockchain. It only takes a minute to sign up.
Sign up to join this community
I need to monitor contract events and perform off-chain processing. How do I uniquely identify a contract event? Can I use a combination of these fields? - transactionHash - transactionIndex - logIndex
I supposed I cannot use transactionHash alone because 1 transaction may emit multiple events. IMO, the documentation https://github.com/ethereum/wiki/wiki/JavaScript-API#contract-events doesn't describe the fields transactionIndex and logIndex well.
If two events are logged in one transaction, transactionIndex is going to be the same.
Using transactionHash and logIndex should enable you to identify unique event logs.
transactionIndex is the index of the transaction in the block. The logIndex is the index of the log in the block logs
`${transactionhash}-${logIndex}` is unique to each log, thanks for nailing it down!
You can only uniquely identify an event within the context of a block. As per https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_getfilterchanges, the logIndex refers to position within a block, so you'll probably have to go with blockHash+txHash+logIndex combo. If not, a reorg can happen, and the same combination of txHash+logIndex can refer to a different event.
