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+# Migrations
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+
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+Migrations for the app environment live in this folder, and use the [East](https://github.com/okv/east) migration
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+framework.
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+
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+We have an npm script which wraps east: `npm run migrations -- ...`
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+
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+For example:
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+
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+``` sh
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+npm run migrations -- list -t 'saas'
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+```
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+
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+### Environments and Tags
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+
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+Overleaf is deployed in three different environments:
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+
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+- `server-ce`: community edition installations (the base system)
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+- `server-pro`: server pro installations
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+- `saas`: the production overleaf site
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+
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+All migrations are tagged with the environments they should run in.
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+For example, a migration that should run in every environment would be tagged with `['server-ce', 'server-pro', 'saas']`.
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+
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+When invoking east, we specify the relevant tags with the `-t` or `--tags` flag.
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+Our adapter will refuse to run if this flag is not set.
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+
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+
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+### Creating new migrations
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+
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+To create a new migration, run:
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+
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+```
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+npm run migrations -- create <migration name>
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+```
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+
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+This command will create a new migration file in the migrations folder, based on a template. The template provides
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+`migrate` and `rollback` methods, which are run by the `east` binary when running the migrations. `rollback` should
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+undo the changes made in `migrate`.
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+
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+#### Running scripts as a migration
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+
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+To run a script in a migration file, look at `migrations/20190730093801_script_example.js`, which runs the script
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+`scripts/example/script_for_migration.js`. This uses a method where the script can be run standalone via `node`, or
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+through the migrations mechanism.
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+
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+### Running migrations
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+
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+To run all migrations in a server-ce environment:
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+``` sh
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+npm run migrations -- migrate -t 'server-ce'
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+```
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+
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+To run all migrations in a saas environment:
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+``` sh
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+npm run migrations -- migrate -t 'saas'
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+```
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+
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+The `-t` flag also works with other `east` commands like `rollback`, and `list`.
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+
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+For other options, or for information on how to roll migrations back, take a look at the
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+[East](https://github.com/okv/east) documentation.
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+
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+### Tips
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+
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+Try to use Mongo directly via the `db` object instead of using Mongoose models. Migrations will need to run in the
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+future, and model files can change. It's unwise to make the migrations depend on code which might change.
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+
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+**Note:** Running `east rollback` without any arguments rolls back *all* migrations, which you may well not want.
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