migrate

Call v334 → current #9

Runs migration logic for contracts after a runtime upgrade.

View calls on chain

Call Workflow

migrate

1. Validation

Signature, nonce, mortality, fees

Signature

Nonce

Mortality

Fee payment

2. Pre-dispatch

Permission & state checks

Permission checks

State validation

3. Dispatch

Execute logic, modify state

MigrationInProgress ContractInfoOf CodeInfoOf

4. Post-dispatch

Final result & fee settlement

ExtrinsicSuccess

Fees settled

Svelte Flow

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Used by: developers

The Big Picture

When the Contracts pallet itself upgrades, existing contract data may need transformation. This call runs that migration incrementally. Usually automated by the runtime, but can be called manually to control migration pacing or complete stuck migrations.

Why This Matters

Runtime upgrades may change how contract data is stored. Without migration, old contracts could malfunction. This ensures backward compatibility by transforming data to the new format.

Example Scenario

Chain upgraded from Contracts v8 to v9 with new storage layout. Query MigrationInProgress - returns Some(cursor). Contracts may fail until migrated. Call migrate(weight_limit=1000000). Repeat until MigrationInProgress returns None. All contracts now work correctly.

Common Questions

Is migration automatic?: Usually yes - runtime hooks run migration. Manual calls are for edge cases or controlling migration pace on resource-constrained chains.
What if I don't migrate?: Contracts may return errors or wrong data. Some calls may panic. Always complete migrations before expecting normal operation.
How do I know migration is needed?: Check MigrationInProgress storage. Some(cursor) = migration pending. None = no migration needed or migration complete.

Use Cases

Complete pending contract pallet migrations
Ensure contracts work after runtime upgrades
Administrative maintenance after chain upgrades

From Chain Metadata

When a migration is in progress, this dispatchable can be used to run migration steps. Calls that contribute to advancing the migration have their fees waived, as it's helpful for the chain. Note that while the migration is in progress, the pallet will also leverage the `on_idle` hooks to run migration steps.

Input Parameters

#	Name	Type	Description
0	weight_limit	Weight	weight_limit (Weight)

Permissions

Origin

Unknown

Required Role

Any

Permission data inferred from metadata. May be incomplete.

Requirements

Runtime upgrade changed contract storage format
Migration is pending (MigrationInProgress is Some)
Caller has appropriate privileges
Weight limit sufficient for migration step

Effects

Storage Modified

MigrationInProgress ContractInfoOf CodeInfoOf

Postconditions

Contract storage migrated to new format
MigrationInProgress updated or cleared
Migrated contracts functional under new runtime

Side Effects

May need multiple calls to complete full migration
Contracts may be unusable until migration completes

Code Examples

import { ApiPromise, WsProvider } from "@polkadot/api";
import { stringCamelCase } from "@polkadot/util";

const provider = new WsProvider("wss://entrypoint-finney.opentensor.ai:443");
const api = await ApiPromise.create({ provider });

// Build migrate call
const weight_limit = 0 as any /* Weight */;

const call = api.tx[stringCamelCase("Contracts")][stringCamelCase("migrate")](
  weight_limit
);

Runtime Info

Pallet Index: 29
Call Index: 9
First Version: v334
Current Version: v393

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