python - Alembic 自动生成不检测具有大小写混合名称的现有表

Question

当我想使用 alembic 进行自动生成迁移时出现错误。

项目树:

-   alembic.ini
-   axis.py
-   tree.txt
-   
    alembic
   -   env.py
   -   README
   -   script.py.mako

       versions

# A generic, single database configuration.

[alembic]
# path to migration scripts
script_location = alembic

# 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 alembic/versions.  When using multiple version
# directories, initial revisions must be specified with --version-path
# version_locations = %(here)s/bar %(here)s/bat alembic/versions

# the output encoding used when revision files
# are written from script.py.mako
# output_encoding = utf-8

sqlalchemy.url = mysql+pymysql://root:**********$@localhost/amatdb_test


[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

# 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

轴.py

from sqlalchemy import create_engine
import pymysql
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint

Base = declarative_base()
engine = create_engine('mysql+pymysql://root:*******$@localhost/amatdb_test')

#The axis on which the tests are executed
class AXIS(Base):
    __tablename__ = 'Axis'
    id_axis        = Column(Integer, primary_key = True)
    name_axis      = Column(String(10), nullable=False)

env.py

from logging.config import fileConfig
from sqlalchemy import engine_from_config
from sqlalchemy import pool

from alembic import context

import sys
import os

sys.path.insert(0, os.getcwd())
print(sys.path)
from axis import Base

print(Base.metadata.sorted_tables)


# 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 = 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"},
    )

    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()

我的问题说明

首先，我创建了我的第一个自动生成迁移:alembic revision --autogenerate

迁移文件似乎是正确的。

"""Creation table

Revision ID: dcd02a3f6ff9
Revises: 
Create Date: 2020-06-03 08:47:48.198022

"""
from alembic import op
import sqlalchemy as sa


# revision identifiers, used by Alembic.
revision = 'dcd02a3f6ff9'
down_revision = None
branch_labels = None
depends_on = None


def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.create_table('Axis',
    sa.Column('id_axis', sa.Integer(), nullable=False),
    sa.Column('name_axis', sa.String(length=10), nullable=False),
    sa.PrimaryKeyConstraint('id_axis')
    )
    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.drop_table('Axis')
    # ### end Alembic commands ###

然后，我运行:alembic upgrade head

我的数据库已创建。

因此，我向表轴添加了一个名为“test”的新列。

test           = Column(String(10), default=None)

我第二次运行: alembic revision --autogenerate
我获得了这个迁移文件

"""Ajout colonne test dans axis

Revision ID: 283ca08aec66
Revises: dcd02a3f6ff9
Create Date: 2020-06-03 08:49:19.717515

"""
from alembic import op
import sqlalchemy as sa
from sqlalchemy.dialects import mysql

# revision identifiers, used by Alembic.
revision = '283ca08aec66'
down_revision = 'dcd02a3f6ff9'
branch_labels = None
depends_on = None


def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.create_table('Axis',
    sa.Column('id_axis', sa.Integer(), nullable=False),
    sa.Column('name_axis', sa.String(length=10), nullable=False),
    sa.Column('test', sa.String(length=10), nullable=True),
    sa.PrimaryKeyConstraint('id_axis')
    )
    op.drop_table('axis')
    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.create_table('axis',
    sa.Column('id_axis', mysql.INTEGER(), autoincrement=True, nullable=False),
    sa.Column('name_axis', mysql.VARCHAR(length=10), nullable=False),
    sa.PrimaryKeyConstraint('id_axis'),
    mysql_collate='utf8mb4_0900_ai_ci',
    mysql_default_charset='utf8mb4',
    mysql_engine='InnoDB'
    )
    op.drop_table('Axis')
    # ### end Alembic commands ###

如您所见，alembic 尝试重新创建表格轴。所以，当我运行时: alembic upgrade head
我收到一个错误，因为轴已经存在。

我错过了什么 ？

为什么 Alembic 无法检测到现有表？

感谢您的时间和考虑

Answer 1

尝试使用小写的表名，即。 axis而不是 Axis .我不确定 mysql 甚至支持大写表名，但这可能会导致问题。

可能发生的情况的一个例子，mysql 可能会默默地将名称小写，因此第一次使用 alembic 比较 Axis无所事事，去做 Axis它可以工作，但 mysql 默默地创建 axis .第二次alembic看没有Axis ，所以它试图创建 Axis再次，mysql 小写它并创建表失败，因为 axis已经存在。此外，Alembic 锯还有一个 axis ，所以它会删除该表，因为它不是 Axis而不是在 sqlalchemy 模式中。

无论哪种方式，只使用小写字母都可能更安全。