Skip to main content
Version: Old ArrowSquid docs

JSON format support

Table Implementation

The @subsquid/file-store-json package provides a Table implementation for writing to JSON and JSONL files. Use it by supplying one or more of its instances via the tables field of the Database constructor argument. The Table uses a constructor with the following signature:

Table<S extends Record<string, any>>(fileName: string, options?: {lines?: boolean})


  • S is a Typescript type describing the schema of the table data.
  • fileName: string is the name of the output file in every dataset partition folder.
  • options?: {lines?: boolean} are table options. At the moment the only available setting is whether to use JSONL instead of a plain JSON array (default: false).


This saves ERC20 Transfer events captured by the processor to a JSONL file where each line is a JSON serialization of a {from: string, to: string, value: number} object. Full squid code is available in this repo.

import {Database} from '@subsquid/file-store'
import {Table} from '@subsquid/file-store-json'


const dbOptions = {
tables: {
TransfersTable: new Table<{
from: string,
to: string,
value: bigint
}>('transfers.jsonl', { lines: true })
dest: new LocalDest('./data'),
chunkSizeMb: 10,
syncIntervalBlocks: undefined
} Database(dbOptions), async (ctx) => {
let from: string = ...
let to: string = ...
let value: bigint = ...{ from, to, value })