ERC20

Source: examples/erc20/ Status: Live on The Graph Studio (Arbitrum One)

Indexes ERC20 Transfer events. The simplest possible subgraph — one event, one entity.

Schema

type Transfer @entity {
  id: ID!
  from: Bytes!
  to: Bytes!
  value: BigInt!
  blockNumber: BigInt!
  timestamp: BigInt!
  transactionHash: Bytes!
}

Handler

#![allow(unused)]
fn main() {
pub fn handle_transfer_impl(raw: &RawEthereumEvent) {
    let event = match ERC20TransferEvent::from_raw_event(raw) {
        Ok(e) => e,
        Err(_) => return,
    };

    let id = format!("{}-{}", hex_bytes(&event.tx_hash), hex_bytes(&event.log_index));

    Transfer::new(&id)
        .set_from(event.from.to_vec())
        .set_to(event.to.to_vec())
        .set_value(event.value)
        .set_block_number(event.block_number)
        .set_timestamp(event.block_timestamp)
        .set_transaction_hash(event.tx_hash.to_vec())
        .save();
}
}

Tests

The example includes three tests:

• transfer_creates_entity — verifies the entity is created with correct field values.
• transfer_entity_count — verifies upsert behaviour (same tx hash = same ID = 1 entity) and that different tx hashes produce distinct entities.

cd examples/erc20
cargo test

Key Points

• Entity ID is {tx_hash_hex}-{log_index_hex} — globally unique per log entry.
• The handler uses the lower-level handle_transfer_impl(raw: &RawEthereumEvent) pattern (no #[handler] macro) — the WASM entry point is written manually. Both approaches work identically.
• All numeric fields (value, blockNumber, timestamp) are little-endian Vec<u8> BigInt bytes.