Handle database migrations

CONTRIBUTING.md

@@ -77,4 +77,20 @@ If you want to add new data files, especially for public transportation stops
 3. Write a preprocessing function in `flatisfy/data_files/__init__.py`. You
    can have a look at the existing functions for a model.
 
+
+## Adding new migrations
+
+If you want to change the database schema, you should create a matching
+migration. Here is the way to do it correctly:
+
+1. First, edit the `flatisfy/models` files to create / remove the required
+   fields. If you create a new database from scratch, these are the files
+   which will be used.
+2. Then, run `alembic revision -m "Some description"` in the root of the git
+   repo to create a new migration.
+3. Finally, edit the newly created migration file under the `migrations/`
+   folder to add the required code to alter the database (both upgrade and
+   downgrade).
+
+
 Thanks!

alembic.ini

@@ -0,0 +1,74 @@
+# A generic, single database configuration.
+
+[alembic]
+# path to migration scripts
+script_location = migrations
+
+# template used to generate migration files
+# file_template = %%(rev)s_%%(slug)s
+
+# timezone to use when rendering the date
+# within the migration file as well as the filename.
+# string value is passed to dateutil.tz.gettz()
+# leave blank for localtime
+# timezone =
+
+# max length of characters to apply to the
+# "slug" field
+#truncate_slug_length = 40
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# set to 'true' to allow .pyc and .pyo files without
+# a source .py file to be detected as revisions in the
+# versions/ directory
+# sourceless = false
+
+# version location specification; this defaults
+# to migrations/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path
+# version_locations = %(here)s/bar %(here)s/bat migrations/versions
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+sqlalchemy.url = sqlite:///data/flatisfy.db
+
+
+# Logging configuration
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

doc/0.getting_started.md

@@ -208,3 +208,13 @@ If you want to build the web assets, you can use `npm run build:dev`
 (respectively `npm run watch:dev` to build continuously and monitor changes in
 source files). You can use `npm run build:prod` (`npm run watch:prod`) to do
 the same in production mode (with minification etc).
+
+
+## Upgrading
+
+To update the app, you can simply `git pull` the latest version. The database
+schema might change from time to time. Here is how to update it automatically:
+
+* First, edit the `alembic.ini` file and ensure the `sqlalchemy.url` entry
+  points to the database URI you are actually using for Flatisfy.
+* Then, run `alembic upgrade head` to run the required migrations.

migrations/README

@@ -0,0 +1 @@
+Generic single-database configuration.

migrations/env.py

@@ -0,0 +1,70 @@
+from __future__ import with_statement
+from alembic import context
+from sqlalchemy import engine_from_config, pool
+from logging.config import fileConfig
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+# from myapp import mymodel
+# target_metadata = mymodel.Base.metadata
+target_metadata = None
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def run_migrations_offline():
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url, target_metadata=target_metadata, literal_binds=True)
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online():
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+    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
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

migrations/script.py.mako

@@ -0,0 +1,24 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision = ${repr(up_revision)}
+down_revision = ${repr(down_revision)}
+branch_labels = ${repr(branch_labels)}
+depends_on = ${repr(depends_on)}
+
+
+def upgrade():
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade():
+    ${downgrades if downgrades else "pass"}

migrations/versions/8155b83242eb_add_is_expired.py

@@ -0,0 +1,30 @@
+"""Add is_expired
+
+Revision ID: 8155b83242eb
+Revises:
+Create Date: 2018-10-16 22:51:25.442678
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = '8155b83242eb'
+down_revision = None
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column(
+        'flats',
+        sa.Column('is_expired', sa.Boolean(), default=False)
+    )
+
+
+def downgrade():
+    op.drop_column(
+        'flats',
+        'is_expired'
+    )

requirements.txt

@@ -1,3 +1,4 @@
+alembic
 appdirs
 arrow
 backports.csv; python_version < '3.0'