Skip to main content
Version: Firesquid

Data mapping

EvmBatchProcessor assumes single batch handler via the method:<Store>(db: Database<Store>, batchHandler: (ctx: BatchContext<Store>) => Promise<void>)

The batch handler ingests the incoming archive data stored in ctx.block, transforms it, and persists using the interface.

BatchContext interface

EvmBatchProcessor defines a single data handler which is a pure function accepting a single argument of type BatchContext. BatchContext has the following structure

export interface BatchContext<Store, Item> {
* An internal handle
_chain: Chain
// a logger to be used within the handler
log: Logger
// the facade interface for the target database
store: Store
// input on-chain data as requested by the subscriptions
blocks: BatchBlock<Item>[]


The blocks field holds the log item data to be processed, aligned at the block level.

export interface BatchBlock<Item> {
* Block header
header: EvmBlock

* A unified log of events and calls.
* List of the block events is a subsequence
* of the unified execution log.
items: Item[]

BatchBlock.header contains the block header data. BatchBlock.items is a unified log containing the event and the call data. All events emitted by a call are placed before the call itself. All the child calls are placed before the parent call.

Each Item has the following structure:

// either it's an `event` or `transaction` item
kind: `evmLog` | `transaction`,
// EVM address emitted the log or the transaction destination
address: string,
// the evm log data as specified by the corresponding `addLog()` or `addTransaction()` data selectors
evmLog?: {},
// the transaction data as specified by the corresponding `addLog()` or `addTransaction()` data selectors
transaction?: {}

The types of evmLog and transaction are inferred from the data selectors set by the corresponding processor.addLog() and processor.addTransaction() init methods of EvmBatchProcessor (see the previous page).


A concrete instance is derived at runtime from the run argument via<Store>(db: Database<Store>, batchHandler: (ctx: BatchContext<Store>) => Promise<void>)

The most commonly used is a TypeORM-like interface extended with additional support for batch updates. The core Squid SDK currently maintains only Postgres-compatible stores, with third-party support for other databases.

See Store Interface for details.


The log field is a dedicated Logger instance to be used for debug and otherwise. See Logging for more details.


The handler below simply outputs all the log items emitted by the contract 0x2E645469f354BB4F5c8a05B3b30A929361cf77eC and saves some bogus data to the store:

import { Store, TypeormDatabase } from "@subsquid/typeorm-store";
import {EvmBatchProcessor} from '@subsquid/evm-processor'
import { MyEntity } from "./model/generated/myEntity.model";

const processor = new EvmBatchProcessor()
archive: '',
.setBlockRange({ from: 6175243 })
.addLog('0x2E645469f354BB4F5c8a05B3b30A929361cf77eC', {
filter: [[ ]],
data: {
evmLog: {
topics: true,
data: true,
} as const,
}); TypeormDatabase(), async (ctx) => {
for (const c of ctx.blocks) {
for (const i of c.items) {, `Item:`)
new MyEntity({id: '1', foo: 'bar'}),
new MyEntity({id: '2', foo: 'baz'})

One can experiment with the data selectors and see how the output changes depending on it.

For a more elaborate example, check the Gravatar squid and the EVM Examples.