We have some elaborate logic in a a @hybrid_property and
@<hybrid_property>.expression that I'm keen on setting up some testing to
ensure that both cases return the same value. I'm having some difficulty
sorting out when each version is used at any given time though.
@hybrid_property
def testProp(self):
...etc...
@testProp.expression(cls):
...etc...
...
# This query generated from this does not include 'test_prop' in
the select.
orm_obj = Task.query.filter(Task.id == '30340').one()
# It then executes through the @hybrid_property (python) code when
you access it.
print (orm_obj.test_prop)
# This version runs through the @testProp.expression at query
runtime, generating the value from the select
tuples = Task.query.filter(Task.id == '30340').with_entities(Task.
test_prop)
# And of course accessing the tuple here doesn't run the
@hybrid_property code, as it's already there.
print (tuples[0].test_prop)
I understand that one is an instance vs a class property, but during the
query processing it's not clear to me when/why one would be used vs the
other. Is the 'with_entities' doing something here? What other cases
would the expression version be used? I'm just looking for some help
understanding the when/where/why of these. I'd really love to NOT write the
expression version at all if possible (we won't need to filter on it in the
query or anything), because in our case, it's just begging for us to
introduce bugs via inconsistent implementations of the same intended logic.
--
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