Hi.
Imagine the following scenario:
session = DBSession()
readonly_model = session.query(ReadOnlyModel).get(id)
# Readonly means the model will NOT have its data changed in the life of
the transaction(s).
method_one(readonly_model.readonly_data, param_1, param_2, ...)
method_two(readonly_model.readonly_data, param_3, param_4, ...)
session.commit()
Now, the code here is the "caller" and the methods one and two are
logically separate, meaning they do not know anything about the caller,
nor the caller knows anything about the internal states and processing
involved in the methods.
Suppose a transaction fails in one or both methods, say an
IntegrityError. The methods know how to handle this, catch the
exceptions and adapt accordingly. They manually do session.rollback()
and proceed within new transaction.
The problem is, if this happens in method_one, then readonly_model is
expired and has no readonly_model.readonly_data when method two is
called. From what I've read in the docs, I am supposed to do
session.refresh(), but that means the caller must know what happened
within the methods one and two (rollback happened).
One way would be to extract data from the readonly_model:
readonly_data = readonly_model.readonly_data
method_one(readonly_data, param_1, param_2, ...)
...
Now, I am certain that this readonly data will NOT change between two
transactions, 100% sure it will never happen in the life of entire
request / all transactions involved in the process, so basically
extracting it from the session/model is safe, within the logic of the code.
Any suggestions/advices about this? Am I doing something completely
wrong? What if the readonly_data was not 100% sure not to change? Is my
only option to have the caller somehow know there was rollback involved
and refresh the session?
Thanks!
--
.oO V Oo.
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