我想让alembic为我做一个数据库迁移.我对我的模型进行了更改,添加了两个新列,这些列将具有基于表中当前行计算的数据.我真正想要做的是弄清楚如何在实际迁移之前测试迁移的内容.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升级–sql 3e0

我收到了来自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 ###

解决方法:

你不能运行这个：

for entry in DBSession.query(SIPEndpoint):

在–sql模式下,因为这是一个SELECT语句.在–sql模式下没有可用于SELECT的数据库.

没有办法对希望与数据库进行对话的脚本进行“干运行”,例如,一个依赖于从数据库中检索数据的脚本. –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,以及极其有限的程度,INSERT,UPDATE和DELETE语句,必须以非常特殊的方式发出,以便它们不会尝试请求有关操作的信息.对于INSERT,建议使用bulk insert样式,因为它与–sql模式兼容.