Add Alembic example files

Author: febus982

docs/manager/alembic/alembic.ini

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+# a multi-database configuration.
+
+[alembic]
+# path to migration scripts
+script_location = alembic
+
+# template used to generate migration file names; The default value is %%(rev)s_%%(slug)s
+# Uncomment the line below if you want the files to be prepended with date and time
+# see https://alembic.sqlalchemy.org/en/latest/tutorial.html#editing-the-ini-file
+# for all available tokens
+file_template = %%(year)d-%%(month).2d-%%(day).2d-%%(hour).2d%%(minute).2d%%(second).2d-%%(rev)s_%%(slug)s
+
+# sys.path path, will be prepended to sys.path if present.
+# defaults to the current working directory.
+prepend_sys_path = .
+
+# timezone to use when rendering the date within the migration file
+# as well as the filename.
+# If specified, requires the python-dateutil library that can be
+# installed by adding `alembic[tz]` to the pip requirements
+# 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 alembic/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path.
+# The path separator used here should be the separator specified by "version_path_separator" below.
+# version_locations = %(here)s/bar:%(here)s/bat:alembic/versions
+
+# version path separator; As mentioned above, this is the character used to split
+# version_locations. The default within new alembic.ini files is "os", which uses os.pathsep.
+# If this key is omitted entirely, it falls back to the legacy behavior of splitting on spaces and/or commas.
+# Valid values for version_path_separator are:
+#
+# version_path_separator = :
+# version_path_separator = ;
+# version_path_separator = space
+version_path_separator = os  # Use os.pathsep. Default configuration used for new projects.
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+# We inject db names and config using env.py in alembic directory
+#databases = engine1, engine2
+
+#[engine1]
+#sqlalchemy.url = driver://user:pass@localhost/dbname
+
+#[engine2]
+#sqlalchemy.url = driver://user:pass@localhost/dbname2
+
+[post_write_hooks]
+# post_write_hooks defines scripts or Python functions that are run
+# on newly generated revision scripts.  See the documentation for further
+# detail and examples
+
+# format using "black" - use the console_scripts runner, against the "black" entrypoint
+# hooks = black
+# black.type = console_scripts
+# black.entrypoint = black
+# black.options = -l 79 REVISION_SCRIPT_FILENAME

docs/manager/alembic/env.py

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+import logging
+import os
+from asyncio import get_event_loop
+
+from alembic import context
+from sqlalchemy import Column, Integer, String
+from sqlalchemy.ext.asyncio import AsyncEngine
+from sqlalchemy_bind_manager import SQLAlchemyAsyncConfig, SQLAlchemyBindManager
+
+################################################################
+## Note: The bind_config, sa_manager and models are normally  ##
+## implemented in an application. This is only an example!    ##
+################################################################
+bind_config = {
+    "default": SQLAlchemyAsyncConfig(
+        engine_url=f"sqlite+aiosqlite:///{os.path.dirname(os.path.abspath(__file__))}/sqlite.db",
+        engine_options=dict(
+            connect_args={
+                "check_same_thread": False,
+            },
+            echo=False,
+            future=True,
+        ),
+    ),
+}
+
+sa_manager = SQLAlchemyBindManager(config=bind_config)
+
+class BookModel(sa_manager.get_bind().model_declarative_base):
+    id = Column(Integer)
+    title = Column(String)
+################################################################
+## Note: The bind_config, sa_manager and models are normally  ##
+## implemented in an application. This is only an example!    ##
+################################################################
+
+
+USE_TWOPHASE = False
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+logger = logging.getLogger("alembic.env")
+target_metadata = sa_manager.get_bind_mappers_metadata()
+db_names = target_metadata.keys()
+config.set_main_option("databases", ",".join(db_names))
+
+
+def run_migrations_offline() -> None:
+    """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.
+
+    """
+    # for the --sql use case, run migrations for each URL into
+    # individual files.
+
+    engines = {}
+    for name in db_names:
+        engines[name] = {}
+        engines[name]["url"] = sa_manager.get_bind(name).engine.url
+
+    for name, rec in engines.items():
+        logger.info(f"Migrating database {name}")
+        file_ = f"{name}.sql"
+        logger.info(f"Writing output to {file_}")
+        with open(file_, "w") as buffer:
+            context.configure(
+                url=rec["url"],
+                output_buffer=buffer,
+                target_metadata=target_metadata.get(name),
+                literal_binds=True,
+                dialect_opts={"paramstyle": "named"},
+            )
+            with context.begin_transaction():
+                context.run_migrations(engine_name=name)
+
+
+def do_run_migration(conn, name):
+    context.configure(
+        connection=conn,
+        upgrade_token=f"{name}_upgrades",
+        downgrade_token=f"{name}_downgrades",
+        target_metadata=target_metadata.get(name),
+    )
+    context.run_migrations(engine_name=name)
+
+
+async def run_migrations_online() -> None:
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+    """
+
+    # for the direct-to-DB use case, start a transaction on all
+    # engines, then run all migrations, then commit all transactions.
+
+    engines = {}
+    for name in db_names:
+        engines[name] = {}
+        engines[name]["engine"] = sa_manager.get_bind(name).engine
+
+    for name, rec in engines.items():
+        engine = rec["engine"]
+        if isinstance(engine, AsyncEngine):
+            rec["connection"] = conn = await engine.connect()
+
+            if USE_TWOPHASE:
+                rec["transaction"] = await conn.begin_twophase()
+            else:
+                rec["transaction"] = await conn.begin()
+        else:
+            rec["connection"] = conn = engine.connect()
+
+            if USE_TWOPHASE:
+                rec["transaction"] = conn.begin_twophase()
+            else:
+                rec["transaction"] = conn.begin()
+
+    try:
+        for name, rec in engines.items():
+            logger.info(f"Migrating database {name}")
+            if isinstance(rec["engine"], AsyncEngine):
+
+                def migration_callable(*args, **kwargs):
+                    return do_run_migration(*args, name=name, **kwargs)
+
+                await rec["connection"].run_sync(migration_callable)
+            else:
+                do_run_migration(name, rec)
+
+        if USE_TWOPHASE:
+            for rec in engines.values():
+                if isinstance(rec["engine"], AsyncEngine):
+                    await rec["transaction"].prepare()
+                else:
+                    rec["transaction"].prepare()
+
+        for rec in engines.values():
+            if isinstance(rec["engine"], AsyncEngine):
+                await rec["transaction"].commit()
+            else:
+                rec["transaction"].commit()
+    except:
+        for rec in engines.values():
+            if isinstance(rec["engine"], AsyncEngine):
+                await rec["transaction"].rollback()
+            else:
+                rec["transaction"].rollback()
+        raise
+    finally:
+        for rec in engines.values():
+            if isinstance(rec["engine"], AsyncEngine):
+                await rec["connection"].close()
+            else:
+                rec["connection"].close()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    loop = get_event_loop()
+    if loop.is_running():
+        loop.create_task(run_migrations_online())
+    else:
+        loop.run_until_complete(run_migrations_online())

docs/manager/alembic/script.py.mako

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+<%!
+import re
+
+%>"""${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 = ${repr(depends_on)}
+
+
+def upgrade(engine_name: str) -> None:
+    globals()[f"upgrade_{engine_name}"]()
+
+
+def downgrade(engine_name: str) -> None:
+    globals()[f"downgrade_{engine_name}"]()
+
+<%
+    db_names = config.get_main_option("databases")
+%>
+
+## generate an "upgrade_<xyz>() / downgrade_<xyz>()" function
+## for each database name in the ini file.
+
+% for db_name in re.split(r',\s*', db_names):
+
+def upgrade_${db_name}() -> None:
+    ${context.get(f"{db_name}_upgrades", "pass")}
+
+
+def downgrade_${db_name}() -> None:
+    ${context.get(f"{db_name}_downgrades", "pass")}
+
+% endfor