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62 lines
3.5 KiB
Markdown
62 lines
3.5 KiB
Markdown
# Database Migration
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This tutorial explains the database migration process in nim-waku.
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# Contributors Guide
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## Database Migration Flow
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Nim-waku utilizes the built-in `user_version` variable that Sqlite provides for tracking the database versions.
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The [user_version](https://github.com/waku-org/nwaku/blob/master/waku/waku_archive/driver/sqlite_driver/migrations.nim) MUST be bumped up for every update on the database e.g, table schema/title change.
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Each update should be accompanied by a migration script to move the content of the old version of the database to the new version.
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The script MUST be added to the respective folder as explained in [Migration Folder Structure](#migration-folder-structure) with the proper naming as given in [ Migration Script Naming](#migration-file-naming).
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The migration is invoked whenever the database `user_version` is behind the target [user_version](https://github.com/waku-org/nwaku/blob/master/waku/waku_archive/driver/sqlite_driver/migrations.nim) indicated in the nim-waku application.
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The respective migration scripts located in the [migrations folder](https://github.com/waku-org/nwaku/tree/master/migrations) will be executed to upgrade the database from its old version to the target version.
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## Migration Folder Structure
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The [migrations folder](https://github.com/waku-org/nwaku/tree/master/migrations) is structured as below.
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```
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migrations/
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├── message_store
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│ ├── 00001_addMessageTable.up.sql
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│ ├── 00002_addSenderTimeStamp.up.sql
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│ ├── ...
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└── peer_store
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└── 00001_addPeerTable.up.sql
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```
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The migration scripts are managed in two separate folders `message_store` and `peer_store`.
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The `message_store` folder contains the migration scripts related to the message store tables. Similarly, the `peer_store` folder contains the scripts relevant to the peer store tables.
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## Migration File Naming
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The files in [migrations folder](https://github.com/waku-org/nwaku/tree/master/migrations) MUST follow the following naming style in order to be properly included in the migration process.
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Files with invalid naming will be eliminated from the migration process.
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`<version number>_<migration script description>.<up|down>.sql`
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- `version number`: This number should match the target value of `user_version`.
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- `migration script description`: A short description of what the migration script does.
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- `up|down`: One of the keywords of `up` or `down` should be selected.
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`up` stands for upgrade and `down` means downgrade.
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### Example
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A migration file with the name `00002_addTableX.up.sql` should be interpreted as:
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- `00002`: The targeted `user_version` number.
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- `addTableX`: What the script does.
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- `up`: This script `upgrade`s the database from `user_version = 00001` to the `user_version = 00002`.
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A downgrade migration file corresponding to the `00002_addTableX.up.sql` can be e.g., `00001_removeTableX.down.sql` and should be interpreted as:
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- `00001`: The targeted `user_version` number.
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- `removeTableX`: What the script does.
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- `down`: This script `downgrade`s the database from `user_version = 00002` to the `user_version = 00001`.
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There can be more than one migration file for the same `user_version`.
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The migration process will consider all such files while upgrading/downgrading the database.
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Note that currently we **DO NOT** support **down migration**.
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# User Guide
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Migrations work out of the box.
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However, if you want to be extra sure, please take a backup of the SQLite database prior to upgrading your nim-waku version since we currently don't support downgrades of DB.
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