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MIGRATIONS.md

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Database Schema Migrations

Introduction

flow-wallet-api supports currently three database engines:

  • sqlite
  • mysql
  • postgresql

GORM is used as an ORM for simplifying database operations. It provides support for automatically migrating DB schema migrations, but no versioning. To address schema versioning, gormigrate is used.

Structure for DB migrations

Each migration must be created as a separate package under migrations/internal. The current pattern for package name is m + <YYYYMMDD>

  • e.g. m20210922.

In order to activate / register the migration, it must be added to migration list in migrations/migrations.go.

ID of the migration can be free form string, but the date from migration package is generally preferred (i.e. 20210922).

Migrating database to a specific schema version

To migrate to a specific schema version, the ID of the migration can be configured to FLOW_WALLET_DATABASE_VERSION environment variable.

NOTE: Rollback to old schema version will result in data loss if added columns / tables had been populated before rollback.

When the database version configuration flag has been left empty, the database is migrated to latest version.

Database migrations in clustered environments

When there are more than one instances of flow-wallet-api running, the DB migrations must be performed under a controlled process, depending on changes.

There's no distributed locking mechanism implemented because the deployment environment can vary, but depending on changes it wouldn't prevent inter-version compatibility changes in case the schema/code change introduces one.