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Self Upgrade & State Migration

Three examples on how to handle updates and state migration:

  1. State Migration: How to implement a migrate method to migrate state between contract updates.
  2. State Versioning: How to use readily use versioning on a state, to simplify updating it later.
  3. Self Update: How to implement a contract that can update itself.

State Migration​

The State Migration example shows how to handle state-breaking changes between contract updates.

It is composed by 2 contracts:

  1. Base: A Guest Book were people can write messages.
  2. Update: An update in which we remove a parameter and change the internal structure.
contracts/basic-updates/update/src/migrate.rs
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The Migration Method​

The migration method deserializes the current state (OldState) and iterates through the messages, updating them to the new PostedMessage that includes the payment field.

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Notice that migrate is actually an initialization method that ignores the existing state ([#init(ignore_state)]), thus being able to execute and rewrite the state.

State Versioning​

The State Versioning example shows how to use Enums to implement state versioning on a contract.

Versioning simplifies updating the contract since you only need to add a new new version of the structure. All versions can coexist, thus you will not need to change previously existing structures.

The example is composed by 2 contracts:

  1. Base: The Guest Book contract using versioned PostedMessages (PostedMessagesV1).
  2. Update: An update that adds a new version of PostedMessages (PostedMessagesV2).
contracts/enum-updates/update/src/versioned_msg.rs
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Self Update​

The Self Update example shows how to implement a contract that can update itself.

It is composed by 2 contracts:

  1. Base: A Guest Book were people can write messages, implementing a update_contract method.
  2. Update: An update in which we remove a parameter and change the internal structure.
contracts/self-updates/base/src/update.rs
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