Module: InstantRecord::LocalSchema

Defined in:
lib/instant_record/local_schema.rb

Overview

Bringing a local database up to the app's current schema, at boot.

DatabaseTasks.prepare_all is the whole story on a server: a process starts in Rails.root, so the relative "db/migrate" that ActiveRecord::Migrator defaults to resolves. In the browser the VM's working directory is "/" while the app is mounted at "/rails", so that path finds nothing: the migrator sees zero migrations, reports nothing pending, and prepare_all is a silent no-op. A returning visitor therefore keeps whatever schema their local database was created with, and the first page touching a table added since fails with "relation does not exist" — which is how two demos broke for anyone who had booted the app before they existed.

Pointing the migrator at absolute paths is not enough, and alone it is worse than the no-op. These databases were built by load_schema, and its assume_migrated_upto_version could only record the versions it could find — which, with the paths broken, was the schema's own version and nothing else. Make every migration discoverable and they all look pending, so boot replays create_table :issues against a database that already has it, the install raises, and the worker never activates.

So the versions are reconciled first, by the rule assume_migrated_upto_version would have used: db/schema.rb describes every migration up to its own version, so a migration older than the highest version this database has recorded is already in it, and gets stamped rather than run. Anything newer is genuinely pending, and is migrated for real.

That inherits one property from assume_migrated_upto_version: a migration back-dated below a version this database already has is taken as applied, not run. On a server db:migrate would run it. Here there is no history to consult — only a schema that was loaded whole — so the version order is the only evidence there is.

Class Method Summary collapse

Class Method Details

.catch_up!(paths) ⇒ Object

Reconcile, then migrate. Takes the paths explicitly because the whole bug is a path that only resolves from the right working directory.



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# File 'lib/instant_record/local_schema.rb', line 50

def catch_up!(paths)
  context = ActiveRecord::MigrationContext.new(paths)
  stamp_migrations_the_loaded_schema_already_contains(context)
  context.migrate
end

.prepare! ⇒ Object

The browser runtime's schema step, in place of a bare prepare_all.



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# File 'lib/instant_record/local_schema.rb', line 36

def prepare!
  ActiveRecord::Tasks::DatabaseTasks.prepare_all

  # On a server the working directory already makes migrations findable,
  # and the stamping below would be wrong there: a back-dated migration on
  # a real migration history is genuinely pending, not implied by a schema
  # load that never happened.
  return unless InstantRecord.browser?

  catch_up!(migration_paths)
end