python - 当我希望通过升级内的 Session 对象更改数据时，如何测试 alembic 迁移？

Question

我正在尝试让 alembic 为我执行数据库迁移。我对我的模型进行了更改，添加了两个新列，这些列将包含根据表中的当前行计算的数据。我真正想做的是弄清楚如何在迁移实际执行之前测试迁移将要执行的操作。我的理解是 --sql 参数允许我这样做。

当我尝试使用 --sql 进行升级以在实际执行之前测试迁移时，使用以下命令行:

alembic -c dev_alembic.ini upgrade --sql 3e0

我收到来自 alembic 的错误:

BEGIN TRANSACTION;

CREATE TABLE alembic_version (
    version_num VARCHAR(32) NOT NULL
);

GO

-- Running upgrade  -> 3e076afb70e1

ALTER TABLE sipendpoint ADD extension VARCHAR(50) NULL;

GO

ALTER TABLE sipendpoint ADD home_site VARCHAR(5) NULL;

GO

Traceback (most recent call last):
  File "/home/pgrace/venv/pyramid27/bin/alembic", line 9, in <module>
    load_entry_point('alembic==0.7.6', 'console_scripts', 'alembic')()
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/alembic/config.py", line 439, in main
    CommandLine(prog=prog).main(argv=argv)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/alembic/config.py", line 433, in main
    self.run_cmd(cfg, options)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/alembic/config.py", line 416, in run_cmd
    **dict((k, getattr(options, k)) for k in kwarg)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/alembic/command.py", line 165, in upgrade
    script.run_env()
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/alembic/script.py", line 390, in run_env
    util.load_python_file(self.dir, 'env.py')
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/alembic/util.py", line 243, in load_python_file
    module = load_module_py(module_id, path)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/alembic/compat.py", line 79, in load_module_py
    mod = imp.load_source(module_id, path, fp)
  File "alembic/env.py", line 65, in <module>
    run_migrations_offline()
  File "alembic/env.py", line 44, in run_migrations_offline
    context.run_migrations()
  File "<string>", line 7, in run_migrations
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/alembic/environment.py", line 738, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/alembic/migration.py", line 309, in run_migrations
    step.migration_fn(**kw)
  File "/home/pgrace/repo/stackcallrouterserver/alembic/versions/3e076afb70e1_add_extension_field_and_home_site_to_.py", line 48, in upgrade
    for entry in DBSession.query(SIPEndpoint):
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2515, in __iter__
    return self._execute_and_instances(context)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2528, in _execute_and_instances
    close_with_result=True)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2519, in _connection_from_session
    **kw)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 882, in connection
    execution_options=execution_options)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 887, in _connection_for_bind
    engine, execution_options)
  File "/home/pgrace/venv/pyramid27/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 344, in _connection_for_bind
    transaction = conn.begin()
AttributeError: 'MockConnection' object has no attribute 'begin'

这是有问题的迁移文件:

# revision identifiers, used by Alembic.
revision = '3e076afb70e1'
down_revision = None
branch_labels = None
depends_on = None

from alembic import op
import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base
import re
from scrserver.models import SIPEndpoint

from sqlalchemy.orm import (
    scoped_session,
    sessionmaker,
    )

DBSession = scoped_session(sessionmaker(bind=op.get_bind()))
Base = declarative_base()
Base.metadata.bind = op.get_bind()

def sitecheck(x):
    try:
        return {
                '1.2.3.4': "FOO",
                '5.6.7.8': "BAR",
                '9.10.11.12': "BAZ"
                }
    except KeyError:
        return None

def upgrade():
    ### commands auto generated by Alembic - please adjust! ###
    op.add_column('sipendpoint', sa.Column('extension', sa.String(length=50), nullable=True))
    op.add_column('sipendpoint', sa.Column('home_site', sa.String(length=5), nullable=True))

    ### end Alembic commands ###


    for entry in DBSession.query(SIPEndpoint):
        update=sa.update(SIPEndpoint).where(SIPEndpoint.addr==entry.addr).values(extension=entry.addr)
        op.execute(update)


def downgrade():
    ### commands auto generated by Alembic - please adjust! ###
    op.drop_column('sipendpoint', 'home_site')
    op.drop_column('sipendpoint', 'extension')
    ### end Alembic commands ###

Answer 1

你不能运行这个:

for entry in DBSession.query(SIPEndpoint):

在 --sql 模式下，因为那是一个 SELECT 语句。在 --sql 模式下没有可供选择的数据库。

没有办法对希望与数据库进行对话的脚本进行“试运行”，例如依赖于从数据库 检索数据的脚本。 --sql 模式仅限于那些根本不需要交互的命令，例如CREATE、DROP 和 ALTER 语句，以及 极其有限 程度的 INSERT、UPDATE 和 DELETE 语句，它们必须以非常特殊的方式发出，这样它们就不会尝试请求有关操作的信息。对于插入，bulk insert推荐样式，因为它旨在与 --sql 模式兼容。