當我希望通過升級中的Session對象更改數據時，如何測試alembic遷移？

Question

我想讓alembic為我做一個數據庫遷移。 我對我的模型進行了更改，添加了兩個新列，這些列將具有基於表中當前行計算的數據。 我真正想要做的是弄清楚如何在實際遷移之前測試遷移的內容。 我的理解是--sql參數允許我這樣做。

當我嘗試使用--sql進行升級以在實際執行之前測試遷移時，使用以下命令行：

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

我收到了來自alembic的錯誤：

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'

這是有問題的遷移文件：

# 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

你不能運行這個：

for entry in DBSession.query(SIPEndpoint):

在--sql模式下，因為這是一個SELECT語句。 在--sql模式下沒有可用於SELECT的數據庫。

沒有辦法對希望與數據庫進行對話的腳本進行“干運行”，例如依賴於從數據庫中檢索數據的腳本。 --sql模式僅限於那些根本不需要交互的命令，例如CREATE，DROP和ALTER語句，以及極其有限的 INSERT，UPDATE和DELETE語句，它們必須以非常特殊的方式發出，以便它們不要嘗試請求有關操作的信息。 對於INSERT，建議使用批量插入樣式，因為它與--sql模式兼容。