我正在使用 sqlalchemy、postgres 和 alembic 開發一個應用程式。
專案結構如下：
.
├── alembic.ini
├── main.py
├── migrations
│ ├── env.py
│ ├── README
│ ├── script.py.mako
│ └── versions
├── models
│ ├── base.py
│ ├── datamodel1.py
│ ├── datamodel2.py
│ └── __init__.py
└── requirements.txt
3 directories, 10 files
其中：
的內容models/base.py是：
from sqlalchemy.ext.declarative.api import declarative_base, DeclarativeMeta
Base: DeclarativeMeta = declarative_base()
的內容models/datamodel1.py是：
from models.base import Base
from sqlalchemy.sql.schema import Column
from sqlalchemy.sql.sqltypes import String, Date, Float
class Model1(Base):
__tablename__ = 'model1_table'
model1_id = Column(String, primary_key=True)
col1 = Column(String)
col2 = Column(String)
的內容models/datamodel2.py是：
from models.base import Base
from sqlalchemy.orm import relationship
from sqlalchemy.sql.sqltypes import String, Integer, Date
from sqlalchemy.sql.schema import Column, ForeignKey
# The many to may relationship table
class Model1Model2(Base):
__tablename__ = 'model1_model2_table'
id = Column(Integer, primary_key=True)
model_1_id = Column(String, ForeignKey('model1.model1_id'))
model_2_id = Column(Integer, ForeignKey('model2.model2_id'))
class Model2(Base):
__tablename__ = 'model2_table'
model2_id = Column(Integer, primary_key=True)
model2_col1 = Column(String)
model2_col2 = Column(Date)
# Many to many relationship
model1_model2 = relationship('Model1', secondary='model1_model2_table', backref='model1_table')
的內容migrations/env.py是：
from logging.config import fileConfig
from sqlalchemy import engine_from_config
from sqlalchemy import pool
from alembic import context
import sys
sys.path.append('./')
# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config
# I added the following 2 lines to replace the sqlalchemy.url in alembic.ini file.
db_string = f'postgresql psycopg2://{db_username}:{db_password}@{db_host}:{db_port}/{db_name}'
config.set_main_option('sqlalchemy.url', db_string)
# 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
from models.datamodel1 import Model1
from models.datamodel2 import Model2, Model1Model2
from models.base import Base
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.
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,
dialect_opts={"paramstyle": "named"},
include_schemas=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,
include_schemas=True
)
with context.begin_transaction():
context.run_migrations()
if context.is_offline_mode():
run_migrations_offline()
else:
run_migrations_online()
至于alembic.ini檔案我沒有做任何更改，我只是評論了這一行：
sqlalchemy.url = driver://user:pass@localhost/dbname
因為我把它分配在 migrations/env.py
當我進行更改并運行時alembic revision --autogenerate -m 'Add new updates'，會正確生成遷移檔案，并且一切正常。
但是當我alembic revision --autogenerate -m 'Add new updates'在沒有變化的情況下運行時，它會在終端中顯示：
INFO [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO [alembic.runtime.migration] Will assume transactional DDL.
INFO [alembic.ddl.postgresql] Detected sequence named 'model2_table_model2_id_seq' as owned by integer column 'model2_table(model2_id)', assuming SERIAL and omitting
INFO [alembic.ddl.postgresql] Detected sequence named 'model1_model2_table_id_seq' as owned by integer column 'model1_model2_table(id)', assuming SERIAL and omitting
Generating /home/user/projects/dev/project/migrations/versions/45c6fbdbd23c_add_new_updates.py ... done
并生成包含以下內容的空遷移檔案：
"""Add new updates
Revision ID: 45c6fbdbd23c
Revises: 5c17014a7c18
Create Date: 2021-12-27 17:11:13.964287
"""
from alembic import op
import sqlalchemy as sa
# revision identifiers, used by Alembic.
revision = '45c6fbdbd23c'
down_revision = '5c17014a7c18'
branch_labels = None
depends_on = None
def upgrade():
# ### commands auto generated by Alembic - please adjust! ###
pass
# ### end Alembic commands ###
def downgrade():
# ### commands auto generated by Alembic - please adjust! ###
pass
# ### end Alembic commands ###
這是預期的行為還是與我的架構有關？
如何在沒有更改的情況下防止 Alembic 生成那些空的遷移檔案？
uj5u.com熱心網友回復：
這是預期的行為還是與我的架構有關？
這是預期的行為。命令alembic revision --autogenerate總是創建一個新的遷移檔案。如果不存在任何更改，則它會創建一個空的。
您可以使用alembic-autogen-check來檢查您的遷移是否與模型同步。
~ $ alembic-autogen-check
INFO [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO [alembic.runtime.migration] Will assume transactional DDL.
INFO: Migrations in sync.
如何在沒有更改的情況下防止 Alembic 生成那些空的遷移檔案？
也alembic-autogen-check僅在遷移與模型同步時回傳零代碼。因此，您可以將其用作一個命令
alembic-autogen-check || alembic revision --autogenerate -m 'Add new updates'
不過好像不如單獨使用方便
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標籤：Python PostgreSQL的 sqlalchemy 蒸馏器