Event filtering in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is event filtering in blockchain?

Event filtering means selecting only specific events from the blockchain that match certain rules, so you don't have to look at all events.

beginner

Why do we use event filtering in blockchain applications?

We use event filtering to find only the events we care about, which saves time and computing power because we don't process unnecessary data.

intermediate

How does an event filter work with topics in Ethereum logs?

An event filter uses topics, which are like labels or tags on events, to match and find events that have specific values in those topics.

intermediate

What is the difference between filtering by address and filtering by topics?

Filtering by address means selecting events from a specific contract, while filtering by topics means selecting events based on event parameters or types.

beginner

Give an example of a simple event filter in Ethereum using web3.js.

Example: <br>const filter = {<br>  address: '0x123...',<br>  topics: ['0xabc...']<br>};<br>web3.eth.getPastLogs(filter).then(console.log);<br>This finds past events from the contract at '0x123...' with the first topic '0xabc...'.

What does event filtering help you do in blockchain?

A Delete old blockchain events

B Select only events that match certain criteria

C Create new blockchain events

D Encrypt blockchain events

Event filtering is used to select only the events that match specific rules or criteria.

In Ethereum, what are 'topics' used for in event filtering?

A They label events to help filter by event parameters

B They store the event's timestamp

C They encrypt event data

D They identify the miner of the block

Topics are used to label events and help filter events by their parameters or types.

Which filter option would you use to get events only from a specific smart contract?

A transactionHash

B topics

C blockNumber

D address

The 'address' filter selects events from a specific contract address.

What happens if you do not use event filtering when searching blockchain logs?

A You get all events, which can be slow and large

B You get no events at all

C You only get events from the latest block

D You get encrypted events

Without filtering, you receive all events, which can be very slow and use a lot of resources.

Which method in web3.js is commonly used to get past events with filters?

A subscribe

B sendTransaction

C getPastLogs

D getBlock

The getPastLogs method retrieves past events using filters.

Explain how event filtering improves blockchain application performance.

Think about why you wouldn't want to look at every event.

Describe how you would create a filter to find events from a specific contract with a certain event type.

Remember filters can have multiple parts like address and topics.