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78 lines
2.3 KiB
Python
78 lines
2.3 KiB
Python
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from contextlib import contextmanager
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from sqlalchemy.orm.session import Session
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from sqlalchemy import create_engine
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import os
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cached_engine = None
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def new_engine(database="quickschedule"):
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db_url = os.environ['CLEARDB_DATABASE_URL']
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if db_url:
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uri = 'mysql+pymysql'+db_url[5:].split('?')[0]
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else:
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uri_template = ("mysql+pymysql://{username}:{password}@{host}:"
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"{port}/{database}")
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uri = uri_template.format(username="root",
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password="root",
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host="localhost",
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port=3307,
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database=database if database else '')
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return create_engine(uri,
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isolation_level='READ COMMITTED',
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echo=False,
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connect_args={'charset': 'utf8mb4'})
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def new_session(engine, versioned=True):
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"""Returns a session bound to the given engine."""
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session = Session(bind=engine, autoflush=True, autocommit=False)
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return session
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@contextmanager
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def session_scope(debug=False):
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"""
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Provide a transactional scope around a series of operations.
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Takes care of rolling back failed transactions and closing the session
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when it goes out of scope.
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Note that sqlalchemy automatically starts a new database transaction when
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the session is created, and restarts a new transaction after every commit()
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on the session. Your database backend's transaction semantics are important
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here when reasoning about concurrency.
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Parameters
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----------
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versioned : bool
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Do you want to enable the transaction log?
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debug : bool
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Do you want to turn on SQL echoing? Use with caution. Engine is not
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cached in this case!
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Yields
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------
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Session
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The created session.
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"""
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global cached_engine
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if cached_engine is None:
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cached_engine = new_engine()
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# log.info("Don't yet have engine... creating default from ignition",
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# engine=id(cached_engine))
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session = new_session(cached_engine)
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try:
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yield session
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session.commit()
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except BaseException as exc:
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session.rollback()
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print exc
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raise
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finally:
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session.close()
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