Queried by: developersanalytics
The Big Picture
Allows finding events by their topic (usually event type hash).
Use Cases
- Filter events by type
From Chain Metadata
Mapping between a topic (represented by T::Hash) and a vector of indexes of events in the `<Events<T>>` list. All topic vectors have deterministic storage locations depending on the topic. This allows light-clients to leverage the changes trie storage tracking mechanism and in case of changes fetch the list of events of interest. The value has the type `(T::BlockNumber, EventIndex)` because if we used only just the `EventIndex` then in case if the topic has the same contents on the next block no notification will be triggered thus the event might be lost.
Purpose & Usage
Purpose
Enable efficient event filtering by topic.
Common Query Patterns
- Query by topic hash
Query Keys
| # | Name | Type | Description |
|---|---|---|---|
| 1 | key1 | H256 | key1 (H256) |
Stored Value
Vec<(u32, u32)> Vec
value (Vec<(u32, u32)>)
Code Examples
import { ApiPromise, WsProvider } from "@polkadot/api";
import { stringCamelCase } from "@polkadot/util";
const provider = new WsProvider("wss://entrypoint-finney.opentensor.ai:443");
const api = await ApiPromise.create({ provider });
// Query EventTopics storage
const key1 = 0 as any /* H256 */;
const result = await api.query
[stringCamelCase("System")]
[stringCamelCase("EventTopics")](
key1
);
console.log("EventTopics:", result.toHuman());Runtime Info
- Pallet
- System
- Storage Kind
- Map
- First Version
- v101
- Current Version
- v393