migrate-from-subgraph

name	migrate-from-subgraph
description	Migrate a TheGraph subgraph to Envio Indexer using TDD. Covers schema conversion (remove @entity, Bytes->String, @derivedFrom), handler translation (save->set, store.get->context.get, templates->contractRegister), and verification against subgraph data.
metadata	{"managed-by":"envio"}

TheGraph to Envio Indexer Migration

Migrate from TheGraph subgraph to the Envio Indexer using Test-Driven Development.

Before Starting

Ask the user for:

1. Subgraph GraphQL endpoint (e.g., https://api.thegraph.com/subgraphs/name/org/subgraph)
2. Chain ID and contract addresses
3. Block range for testing (pick blocks with representative events)

The subgraph GraphQL is the source of truth — use it to verify the Envio Indexer produces identical data.

Prerequisites: Subgraph folder in workspace, Node.js v22+, pnpm, Docker

References:

• Envio docs: https://docs.envio.dev/docs/HyperIndex-LLM/hyperindex-complete
• Example (Uniswap v4): https://github.com/enviodev/uniswap-v4-indexer

Quick Reference: Key Differences

TheGraph	Envio
@entity decorator	No decorator needed
Bytes!	String!
entity.save()	context.Entity.set(entity)
store.get("Entity", id)	await context.Entity.get(id)
ContractTemplate.create(addr)	context.addContract(addr) in contractRegister
Direct array access	@derivedFrom (virtual, query via getWhere)
.bind() for RPC	Effect API with context.effect()

Runtime Testing Mandate

After EVERY code change, run pnpm test. TypeScript compilation only catches syntax errors — runtime errors (database issues, missing entities, logic errors) only appear when running the indexer.

See references/step-by-step.md for the full runtime testing checklist.

TDD Migration Flow

1. Query subgraph for expected entity state at specific blocks
2. Write test that processes those blocks and asserts expected output
3. Implement handler until test passes
4. Repeat for each handler

import { describe, it, expect } from "vitest";
import { createTestIndexer } from "envio";

describe("Migration Verification", () => {
  it("Should match subgraph data for Factory.PairCreated", async () => {
    const indexer = createTestIndexer();

    const result = await indexer.process({
      chains: {
        1: { startBlock: 10_000_000, endBlock: 10_000_100 },
      },
    });

    expect(result.changes).toMatchInlineSnapshot(`...`);
  });
});

Run tests: pnpm test

---

Migration Steps Overview

After each step, run: pnpm codegen && pnpm tsc --noEmit && pnpm test

Full step-by-step details with quality checks: references/step-by-step.md

Step 1: Clear Boilerplate

Clear generated event handlers and replace with empty TODO handlers.

Step 2: Migrate Schema

• Remove @entity decorators
• Bytes! → String!
• Keep BigInt!, BigDecimal!, ID!
• ALL entity arrays MUST have @derivedFrom (causes a codegen error without it)
• @derivedFrom arrays are virtual — cannot access in handlers, only API queries

# WRONG — causes "Arrays of entities is unsupported" error
type Transaction { mints: [Mint!]! }

# CORRECT
type Transaction { mints: [Mint!]! @derivedFrom(field: "transaction") }

Run: pnpm codegen (required after schema changes)

Step 3: Refactor File Structure

Mirror subgraph file structure with exact filenames. Update config.yaml with global contract definitions and chain-specific addresses only.

Step 4: Register Dynamic Contracts

For factory-created contracts: add contractRegister BEFORE handler, remove address from dynamic contracts in config.

Factory.PairCreated.contractRegister(({ event, context }) => {
  context.addPair(event.params.pair);
});

Step 5: Implement Handlers (TDD)

Implementation order is critical. See references/step-by-step.md for full 5a/5b/5c/5d breakdown.

1. 5a: Helper functions with no entity dependencies — implement COMPLETE logic, not placeholders
2. 5b: Simple handlers — direct parameter mapping
3. 5c: Moderate handlers — calls helpers, multiple entity updates
4. 5d: Complex handlers — one at a time, with RPC calls and multiple dependencies

External calls MUST use Effect API — see references/migration-patterns.md for Effect API and contract state fetching patterns.

Step 6: Final Verification

Systematic review of every handler and helper function against subgraph. Multiple passes — first pass always misses things. See references/step-by-step.md for full verification checklist.

Step 7: Environment Variables

Search for all process.env references and update .env.example.

---

Code Patterns

Full patterns with examples: references/migration-patterns.md

Entity Creation

// TheGraph:
let entity = new Entity(id);
entity.field = value;
entity.save();

// Envio:
const entity: Entity = {
  id: `${event.chainId}-${id}`,
  field: value,
  blockNumber: BigInt(event.block.number),
  transactionHash: event.transaction.hash,
};
context.Entity.set(entity);

Entity Updates (spread required — entities are read-only)

let entity = await context.Entity.get(id);
if (entity) {
  context.Entity.set({ ...entity, field: newValue });
}

Related Entity Queries (@derivedFrom → getWhere)

// TheGraph: transaction.mints.push(mint);
// Envio:
const mints = await context.Mint.getWhere({ transaction_id: { _eq: transactionId } });

BigDecimal Precision

import { BigDecimal } from "envio";
// NOT: import { BigDecimal } from "bignumber.js";

export const ZERO_BD = new BigDecimal(0);
export const ONE_BD = new BigDecimal(1);
export const ZERO_BI = BigInt(0);
export const ONE_BI = BigInt(1);

Contract State Fetching (.bind() → Effect API)

TheGraph uses .bind() for RPC. Envio requires Effect API with viem. Full pattern: references/migration-patterns.md

---

Common Issues & Fixes

Full quality check guide with 12 common fixes: references/quality-checks.md

Field Names — use _id suffix

// WRONG:  { token0: token0.id }
// CORRECT: { token0_id: token0.id }

Missing async/await

// WRONG:  const entity = context.Entity.get(id);  // Returns {}
// CORRECT: const entity = await context.Entity.get(id);

Note: context.Entity.set() is synchronous — no await needed.

Entity Type Imports

// WRONG:  import { Pair } from "envio";  // Pair is a contract handler, not a type
// CORRECT (when name collides with contract):
import type { Entity } from "envio";
const p: Entity<"Pair"> = { ... };

Schema Type Mapping

Schema	TypeScript
Int!	number
BigInt!	bigint / ZERO_BI
BigDecimal!	BigDecimal / ZERO_BD
String! / Bytes!	string
Entity!	entity_id: string

Multichain IDs

Prefix all entity IDs: ${event.chainId}-${originalId}

---

Reference Files

• Step-by-step guide — Full procedural walkthrough with quality checks after each step
• Migration patterns — Entity CRUD, Effect API, contract state fetching, BigDecimal precision
• Quality checks — 12 common fixes, type mismatches, async/await, field selection
• Migration checklist — 17-point final verification checklist