Alembic usage example guide

README.md

@@ -32,6 +32,8 @@ with engine.connect() as conn:
 
 ```
 
+To setup `alembic` to work with `YDB` please check [this example](https://github.com/ydb-platform/ydb-sqlalchemy/tree/main/examples/alembic).
+
 ## Development
 
 ### Run Tests:

examples/alembic/README.md

@@ -0,0 +1,88 @@
+# Alembic support
+
+In this example we'll see how to use `alembic` with ydb.
+
+## Installation
+
+To make `alembic` work with `YDB` tables please follow these steps:
+
+* Install `ydb-sqlalchemy` package from PyPi:
+
+```bash
+pip install ydb-sqlalchemy`
+```
+
+* Install `alembic` package from PyPi:
+
+```bash
+pip install alembic
+```
+
+## Preparation
+
+We have to setup `alembic` correctly.
+First of all, we should register `YDB` dialect in `env.py`:
+
+```python3
+from alembic.ddl.impl import DefaultImpl
+
+
+class YDBImpl(DefaultImpl):
+    __dialect__ = "yql"
+```
+
+Secondly, since `YDB` do not support updating primary key columns, we have to update alembic table structure.
+For this purpose we should update `run_migrations_online` method in `env.py`:
+
+```python3
+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.
+
+    """
+    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
+        )
+
+        ctx = context.get_context()
+        ctx._version = sa.Table(  # noqa: SLF001
+            ctx.version_table,
+            sa.MetaData(),
+            sa.Column("version_num", sa.String(32), nullable=False),
+            sa.Column("id", sa.Integer(), nullable=True, primary_key=True),
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+```
+
+## Example
+
+To run this example:
+1. Install all dependencies described in `Installation` section.
+1. Update `sqlalchemy.url` field in `alembic.ini` config file.
+1. Run `alembic upgrade head` to apply all migrations:
+
+```bash
+alembic upgrade head
+
+INFO  [alembic.runtime.migration] Context impl YDBImpl.
+INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
+INFO  [alembic.runtime.migration] Running upgrade  -> d91d9200b65c, create series table
+INFO  [alembic.runtime.migration] Running upgrade d91d9200b65c -> 820b994ffa7c, create seasons table
+INFO  [alembic.runtime.migration] Running upgrade 820b994ffa7c -> 9085c679f5dc, create episodes table
+```
+
+To create new migration just add a few changes in `models.py` and run:
+```bash
+alembic revision --autogenerate -m "name of your migration"
+```

examples/alembic/alembic.ini

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+# A generic, single database configuration.
+
+[alembic]
+# path to migration scripts
+# Use forward slashes (/) also on windows to provide an os agnostic path
+script_location = migrations
+
+# 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-%%(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>=3.9 or backports.zoneinfo library.
+# Any required deps can installed by adding `alembic[tz]` to the pip requirements
+# string value is passed to ZoneInfo()
+# 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 ./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:./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 = newline
+version_path_separator = os  # Use os.pathsep. Default configuration used for new projects.
+
+# set to 'true' to search source files recursively
+# in each "version_locations" directory
+# new in Alembic version 1.10
+# recursive_version_locations = false
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+sqlalchemy.url = yql+ydb://localhost:2136/local
+
+
+[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
+
+# lint with attempts to fix using "ruff" - use the exec runner, execute a binary
+# hooks = ruff
+# ruff.type = exec
+# ruff.executable = %(here)s/.venv/bin/ruff
+# ruff.options = --fix REVISION_SCRIPT_FILENAME
+
+# Logging configuration
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARNING
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARNING
+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

examples/alembic/migrations/README

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

examples/alembic/migrations/env.py

@@ -0,0 +1,95 @@
+from logging.config import fileConfig
+
+import sqlalchemy as sa
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+
+from alembic import context
+from alembic.ddl.impl import DefaultImpl
+
+
+# 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.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+# from myapp import mymodel
+# target_metadata = mymodel.Base.metadata
+
+from models import *
+target_metadata = Base.metadata
+
+# 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.
+
+
+class YDBImpl(DefaultImpl):
+    __dialect__ = "yql"
+
+
+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.
+
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+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.
+
+    """
+    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
+        )
+
+        ctx = context.get_context()
+        ctx._version = sa.Table(  # noqa: SLF001
+            ctx.version_table,
+            sa.MetaData(),
+            sa.Column("version_num", sa.String(32), nullable=False),
+            sa.Column("id", sa.Integer(), nullable=True, primary_key=True),
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

examples/alembic/migrations/script.py.mako

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+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}

examples/alembic/migrations/versions/820b994ffa7c_create_seasons_table.py

@@ -0,0 +1,37 @@
+"""create seasons table
+
+Revision ID: 820b994ffa7c
+Revises: d91d9200b65c
+Create Date: 2024-12-10 14:50:44.633728
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '820b994ffa7c'
+down_revision: Union[str, None] = 'd91d9200b65c'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('seasons',
+    sa.Column('series_id', sa.Integer(), nullable=False),
+    sa.Column('season_id', sa.Integer(), nullable=False),
+    sa.Column('title', sa.Unicode(), nullable=True),
+    sa.Column('first_aired', sa.Integer(), nullable=True),
+    sa.Column('last_aired', sa.Integer(), nullable=True),
+    sa.PrimaryKeyConstraint('series_id', 'season_id')
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_table('seasons')
+    # ### end Alembic commands ###