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Alembic usage example guide
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2 changes: 2 additions & 0 deletions README.md
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Expand Up @@ -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:
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78 changes: 78 additions & 0 deletions examples/alembic/README.md
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# 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.
To create new migration just add a few changes in `models.py` and run:
```bash
alembic revision --autogenerate -m "name of your migration"
```
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117 changes: 117 additions & 0 deletions 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
1 change: 1 addition & 0 deletions examples/alembic/migrations/README
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Generic single-database configuration.
95 changes: 95 additions & 0 deletions examples/alembic/migrations/env.py
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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()
26 changes: 26 additions & 0 deletions 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"}
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"""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 ###
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