migrating-motoko
Inline Actor Migration
Migrate actor state across canister upgrades using a migration expression attached to the actor. Each upgrade has at most one migration function.
For multi-step migration with a migrations/ directory, load migrating-motoko-enhanced instead.
What This Is
The (with migration = ...) syntax lets you transform actor state during an upgrade — rename fields, change types, split or merge values. The migration runs exactly once per upgrade; on fresh install, the actor's initializers run normally.
When to Use
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