Migration tests (#636)

Adds some basic tests to ensure our migrations run successfully and
yield the same resulting db schema as our models.

How we do it:
- Create an initial migration from the empty database to the database
before our current first migration
- Leverage pytest-alembic, a plugin that runs these basic tests for you

Pipfile

@@ -15,6 +15,7 @@ pylint = "*"
 black = "==19.10b0"
 snapshottest = "*"
 alembic = "*"
+pytest-alembic = "*"
 
 [packages]
 authlib = "*"

alembic.ini

@@ -2,7 +2,7 @@
 
 [alembic]
 # path to migration scripts
-script_location = migrations
+script_location = server/migrations
 
 # template used to generate migration files
 # file_template = %%(rev)s_%%(slug)s

mypy.ini

@@ -40,4 +40,13 @@ ignore_missing_imports = True
 ignore_missing_imports = True
 
 [mypy-snapshottest]
+ignore_missing_imports = True
+
+[mypy-alembic]
+ignore_missing_imports = True
+
+[mypy-alembic.config]
+ignore_missing_imports = True
+
+[mypy-pytest_alembic.tests]
 ignore_missing_imports = True

server/migrations/README.md

@@ -0,0 +1,29 @@
+# Migrations
+
+We use [Alembic](https://alembic.sqlalchemy.org/en/latest/) to create and run incremental database migrations when we change the Arlo data model.
+
+The Alembic docs have great info on the ins and outs of creating and running migrations, but here's a sample workflow:
+
+## Create a migration script
+
+First, make sure the database is in the existing, unmigrated state (e.g. by checking out the last commit and running `make resetdb`, or restoring from a database backup).
+
+Then, use Alembic to autogenerate a migration script:
+
+    pipenv run alembic revision --autogenerate -m "Some description of the migration"
+
+The resulting migration script will be in `migrations/versions`.
+
+## Edit the migration script
+
+The autogeneration capabilities of Alembic will only get you so far, so you _always_ need to go manually check and edit the script. For example, Alembic won't autogenerate updates to primary key constraints. Read [the docs](https://alembic.sqlalchemy.org/en/latest/autogenerate.html#what-does-autogenerate-detect-and-what-does-it-not-detect) for specific info about the autogeneration capabilities.
+
+Note that we don't support reverse migrations (`alembic downgrade`) because we don't think it's worth the effort to implement them. So you should comment out the autogenerated downgrade code and replace it with `pass`.
+
+## Test the migration script
+
+Populate your local database with some data (e.g. restored from a backup), then run:
+
+    pipenv run alembic upgrade head
+
+...and see if it works!

migrations/env.py → server/migrations/env.py

@@ -22,7 +22,7 @@
 
 # Interpret the config file for Python logging.
 # This line sets up loggers basically.
-fileConfig(config.config_file_name)
+fileConfig(config.config_file_name, disable_existing_loggers=False)
 
 # add your model's MetaData object here
 # for 'autogenerate' support
@@ -39,7 +39,7 @@
 # ... etc.
 
 
-def run_migrations_offline():
+def run_migrations_offline():  # pragma: no cover
     """Run migrations in 'offline' mode.
 
     This configures the context with just a URL
@@ -55,6 +55,9 @@ def run_migrations_offline():
     context.configure(
         url=url,
         target_metadata=target_metadata,
+        compare_type=True,
+        compare_server_default=True,
+        include_schemas=True,
         literal_binds=True,
         dialect_opts={"paramstyle": "named"},
     )
@@ -70,11 +73,14 @@ def run_migrations_online():
     and associate a connection with the context.
 
     """
-    connectable = engine_from_config(
-        config.get_section(config.config_ini_section),
-        prefix="sqlalchemy.",
-        poolclass=pool.NullPool,
-    )
+    connectable = config.attributes.get("connection", None)
+
+    if connectable is None:
+        connectable = engine_from_config(
+            config.get_section(config.config_ini_section),
+            prefix="sqlalchemy.",
+            poolclass=pool.NullPool,
+        )
 
     with connectable.connect() as connection:
         context.configure(connection=connection, target_metadata=target_metadata)
@@ -84,6 +90,6 @@ def run_migrations_online():
 
 
 if context.is_offline_mode():
-    run_migrations_offline()
+    run_migrations_offline()  # pragma: no cover
 else:
     run_migrations_online()