python - 如何使用 SQLAlchemy 将行从本地 SQLite 数据库迁移到远程 MySQL 数据库？

Question

我正在使用 SQLAlchemy 管理 2 个数据库。一个是本地 SQLite DB，另一个是 Google 云平台上的远程 MySQL DB，它们共享相同的架构。我正在尝试将 SQLite 数据库中包含的行附加到 MySQL 数据库。我目前有一个文件定义我的类，如下所示:

传感器集合.py

class Readings(Base):
    __tablename__ = 'readings'

    time = Column(String(250), primary_key=True)
    box_name = Column(String(250))
    FS = Column(Numeric)
    IS = Column(Numeric)
    VS = Column(Numeric)
    CO = Column(Numeric)
    TVOC = Column(Numeric)
    cTemp = Column(Numeric)
    fTemp = Column(Numeric)
    humidity = Column(Numeric)
    pressure = Column(Numeric)

然后我有另一个文件声明我的 Base、Session 和引擎:

基础.py

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

engine = create_engine('sqlite:///%s' % 'db/db.db')
Session = sessionmaker(bind=engine)
Base = declarative_base()

最后是我的实际代码:

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy.schema import Table
from SensorCollection import Readings
from sqlalchemy.sql.expression import insert

# uploads MySQL database to Google cloud server
# uses ORM to ensure the databases can communicate with each other
user = ***
password = ***
host = ***
port = ***
dbName = ***
instanceConnectionName = ***
# create the engine for the local db
engineLocal = create_engine('sqlite:///%s' % 'db/db.db')
BaseLocal = Readings(None, None, None, None, None, None, None, None, None, None, None)

# create the engine for the Google db
engineGoogle = create_engine('mysql+mysqldb://%s@%s:%s/%s?unix_socket=/cloudsql/%s' % (user, host, port, dbName, instanceConnectionName))
SessionGoogle = sessionmaker(bind=engineGoogle)
BaseGoogle = Readings(None, None, None, None, None, None, None, None, None, None, None)

# create the local db
BaseLocal.metadata.create_all(engineLocal)

# create the Google db and start the session
BaseGoogle.metadata.create_all(engineGoogle)
sessionGoogle = SessionGoogle()

# create table objects for each db
t1 = Table('readings', BaseLocal.metadata, autoload=True, autoload_with=engineLocal)
t2 = Table('readings', BaseGoogle.metadata, autoload=True, autoload_with=engineGoogle)

# the first subquery, select all ids from SOME_TABLE where some_field is not NULL
s1 = t1.select()

# the second subquery, select all ids from SOME_TABLE where some_field is NULL
s2 = t2.select()

# union s1 and s2 subqueries together and alias the result as "alias_name"
q = s1.union(s2)

insert(t2, s1)
sessionGoogle.query(q)
# sessionGoogle.add_all(s1)

# commit changes and close the session
sessionGoogle.commit()
sessionGoogle.close()

目前，SQLite 数据库存在得很好，远程服务器也已设置，但代码在连接到 Google 时甚至没有创建表。它似乎连接正确，因为如果我更改任何服务器详细信息，我会收到 MySQL 错误。它也不会给我任何错误。它编译并运行，但不附加数据，甚至不创建表。这是我第一次尝试任何类型的数据库，所以我确信它充满了错误，而且一点也不优雅。任何帮助将不胜感激。

编辑 djkern 帮助我创建了表格，并且我更新了我的代码。不过，我还没有获得要附加的数据。

Answer 1

在您的代码中，您有:

# create the Google db and start the session
BaseLocal.metadata.create_all(engineLocal)
sessionGoogle = SessionGoogle()

你的意思是这样吗？

# create the Google db and start the session
BaseGoogle.metadata.create_all(engineGoogle)
sessionGoogle = SessionGoogle()