Handlers

Handlers are where indexing logic lives. Redstart has three kinds, each mapping to the corresponding manifest section.

Event handlers

handler on Token.Transfer(event) {
  let sender = Account.loadOrCreate(event.params.from, { balance: BigInt.zero })
  let receiver = Account.loadOrCreate(event.params.to, { balance: BigInt.zero })

  sender.balance = sender.balance - event.params.value
  receiver.balance = receiver.balance + event.params.value
  // Both entities are dirty-tracked and auto-saved at handler end.
}

event.params is typed from the ABI. event.block, event.transaction, and event.address are available as usual.

Auto-save, by construction

You never call .save(). Entities you load or create are dirty-tracked and flushed when the handler returns (and at return from any helper). Forgetting to save — one of the most common subgraph bugs — is simply not expressible.

Call & block handlers

handler call Token.transfer(call) {
  // call.inputs / call.outputs are ABI-typed
}

handler block Token every 100 {
  // runs every 100 blocks; `once` is also supported
}

These render to callHandlers and blockHandlers (with the polling/once filter) respectively.

Control flow

Handlers and helpers support if/else if/else, while, and for over numeric ranges and lists, plus array literals and indexing — all lowered to native AssemblyScript:

for holder in holders {
  if holder.balance > BigInt.zero {
    activeCount = activeCount + 1
  }
}