By database we refer to a separate instance (could be on another
server) of equvalent database i.e. production and development
environments.
Using sqlalchemy.ext.declarative, what would be a correct pattern to
enable one model to connect to two equivalent databases?
Consider:
--- model.py ---
Base = declarative_base()
metadata = Base.metadata
class MyTable(Base):
__tablename__ = 'my_table'
id = Column(Integer, primary_key=True, nullable=False)
description = Column(CHAR(length=100), nullable=False)
_Session = sessionmaker()
def make_session(uri):
metadata.bind = engine
session = Session(bind=engine)
return session
--- program.py --
import model
"""copy some data between databases"""
srcdb = model.make_session(srcdb_uri)
destdb = model.make_session(srcdb_uri)
items = srcdb.query(model.MyTable).all()
for i in items:
destdb.merge(i)
destdb.commit()
---
We have two distinct sessions bound to to different databases but
because metadata is a module level variable it gets rebound to the
database of last call.
Also I am somewhat unclear on the difference between metadata binding
to engine and session binding to engine, especially when they end up
different. What is relevance of MetaData binding?
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