Pipe anatomy

Documentation Index

Fetch the complete documentation index at: https://beta.docs.sqd.dev/llms.txt

Use this file to discover all available pages before exploring further.

• A source - typically made with evmPortalSource(). Can have one or more outputs.
• Queries - tell the source which data has to be retrieved to compute each output. A query is defined by a chain call terminated by .build(). Here’s an example:
  evmQuery()
    .addFields({
      block: { timestamp: true },
      log: { address: true, transactionHash: true },
    })
    .addLog({
      topic0: [ TRANSFER_TOPIC ]
    })
    .build()
  
• Per-query transforms (optional) - you can pass data from each query through a chain of simple transforms:
  query
    .pipe(data => data.map(item => ({
      funkyNumber: item.header.timestamp + item.header.number,
      ...item
    })))
    .pipe(someOtherSimpleTransformCallback)
  
  Source object streams the data you get out of each chain of transforms as the value of the corresponding output field.
• Making utils that return reusable query-transform combos is a very useful pattern. In particular, on EVM it is often convenient to keep retrieval and decoding of event logs in a single module. You can easily make such combos with the evmDecoder() function - see the Handling events guide.
• Whole pipe transformers (optional) - use this if you need to compute something based on data originating from multiple queries, or if you need access to per-batch context (cursor, logger, profiler, fork callbacks). Use createTransformer() so the SDK can thread cursor and rollback information (1, 2) through your transform:
  import { createTransformer } from '@subsquid/pipes'
  
  const enrichTransfers = createTransformer<
    { transfers: Transfer[]; approvals: Approval[] },
    { events: EnrichedEvent[] }
  >({
    transform: ({ transfers, approvals }, ctx) => {
      ctx.logger.info({ batch: ctx.stream.state.current?.number }, 'enriching')
      return {
        events: [
          ...transfers.map((t) => ({ kind: 'transfer' as const, ...t })),
          ...approvals.map((a) => ({ kind: 'approval' as const, ...a })),
        ],
      }
    },
  })
  
  evmPortalStream({ /* ... */ }).pipe(enrichTransfers)
  
• Pipe termination: a plain async iterator or a target.
  • If you use the pipe as an async iterator it will throw exceptions if the underlying chain is experiencing reorgs, see Fork handling.
  • We offer two targets out of the box:
    • Postgres via Drizzle
    • ClickHouse
    You can make your own using createTarget().