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12026787
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0
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0
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6
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2012-08-19T13:19:52.930
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2016-05-06T21:44:07.330
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2016-05-06T21:44:07.330
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11722
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298479
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12023526
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2
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13
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When using SQLAlchemy in a Flask app with <a href="http://packages.python.org/Flask-SQLAlchemy/" rel="nofollow noreferrer">Flask-SQLAlchemy</a> it provides a <a href="http://packages.python.org/Flask-SQLAlchemy/signals.html#models_committed" rel="nofollow noreferrer">models_committed</a> signal which receives a list of <code>(model, operation)</code> tuples. Using this signal doing what I'm looking for is extremely easy: <pre><code>@models_committed.connect_via(app) def on_models_committed(sender, changes): for obj, change in changes: if change == 'delete' and hasattr(obj, '__commit_delete__'): obj.__commit_delete__() </code></pre> With this generic function every model that needs on-delete-commit code now simply needs to have a method <code>__commit_delete__(self)</code> and do whatever it needs to do in that method. <hr> It can also be done without Flask-SQLAlchemy, however, in this case it needs some more code: <ul> <li>A deletion needs to be recorded when it's performed. This is be done using the <a href="http://docs.sqlalchemy.org/en/latest/orm/events.html#sqlalchemy.orm.events.MapperEvents.after_delete" rel="nofollow noreferrer"><code>after_delete</code> event</a>.</li> <li>Any recorded deletions need to be handled when a COMMIT is successful. This is done using the <a href="http://docs.sqlalchemy.org/en/latest/orm/events.html#sqlalchemy.orm.events.SessionEvents.after_commit" rel="nofollow noreferrer"><code>after_commit</code> event</a>.</li> <li>In case the transaction fails or is manually rolled back the recorded changes also need to be cleared. This is done using the <a href="http://docs.sqlalchemy.org/en/latest/orm/events.html#sqlalchemy.orm.events.SessionEvents.after_rollback" rel="nofollow noreferrer">after_rollback()</a> event.</li> </ul>
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