The point of hybrid attributes is to allow you to construct a property
that can be evaluated against an instance (in which case it is "normal
python"), or against a class (in which case it needs to return an SQL
expression). *Sometimes* the same python code can work in both
contexts, but only if it is a very simple expression.
Here's your example:
@hybrid_property
def is_id_valid(self):
# some logic here
if self.id % 3 == 0:
return True
else:
return False
If you had already retrieved an instance of GeneralBeqReq from the
database, you could access its "is_id_valid property" and it would
work as expected, because "self.id" would be a normal python integer.
But if you try to access it from the class (ie.
GeneralBeqReq.is_id_valid), it won't do what you expect. "self" will
actually be the class, GeneralBeqReq. "self.id" will be a special
SQLAlchemy "InstrumentedAttribute" object. It happens that
InstrumentedAttributes do support the % operator, returning an SQL
expression object, so "self.id % 3 == 0" will actually return an SQL
expression. But using it inside an "if" statement doesn't make any
sense - you're checking the boolean value of the SQL expression
object, not the result of evaluating it against any particular row. So
GeneralBeqReq.is_id_valid is just going to return a constant (either
True or False, not sure which).
You'd need to add an alternative definition of the is_id_valid
property which returns an SQL expression:
https://docs.sqlalchemy.org/en/14/orm/extensions/hybrid.html#defining-expression-behavior-distinct-from-attribute-behavior
If you can't express your validation function as an SQL expression,
you can't pass it to Query. You'd have to postprocess the query
results in python instead, like this:
a = session.query(GeneralBeqReq)\
.filter(GeneralBeqReq.c.BeqReqStatus == 1)\
.all()
a = [obj for obj in a if obj.is_id_valid]
Simon
On Wed, May 5, 2021 at 4:28 PM Yaakov Bressler <[email protected]> wrote:
>
> Query would be modified to the following:
>
> a = session.query(GeneralBeqReq)\
> .filter(
> GeneralBeqReq.c.BeqReqStatus == 1, # this doesn't look right, but
> whatevz
> GeneralBeqReq.is_id_valid() == True, # a bit redundant, but explicit
> is better than implicit
> )\
> .all()
>
> On Wednesday, May 5, 2021 at 11:26:01 AM UTC-4 Yaakov Bressler wrote:
>>
>> Would it be wrong to assume that the desired function could be added as a
>> hybrid attribute, then queried through the class obj?
>>
>> Example:
>>
>> from sqlalchemy.ext.hybrid import hybrid_property
>>
>> class GeneralBeqReq(Base):
>> ...
>> @hybrid_property
>> def is_id_valid(self):
>> # some logic here
>> if self.id % 3 == 0:
>> return True
>> else:
>> return False
>>
>> On Wednesday, April 28, 2021 at 5:01:32 AM UTC-4 Simon King wrote:
>>>
>>> Parameters that you pass to the Query.filter function are eventually
>>> going to be rendered into an SQL statement, so your is_id_valid
>>> function probably needs to return something built from SQLAlchemy's
>>> SQL expression language:
>>> https://docs.sqlalchemy.org/en/14/core/tutorial.html
>>>
>>> If you can explain the sort of validation that is_id_valid needs to
>>> do, we might be able to help more.
>>>
>>> Simon
>>>
>>>
>>> On Wed, Apr 28, 2021 at 6:33 AM Gyanaranjan Nayak <[email protected]> wrote:
>>> >
>>> > I have a function with name is_id_valid(id) which returns either True or
>>> > False.
>>> >
>>> > I want to pass this function inside a sqlalchemy query inside the filter
>>> > condition.
>>> > My query example is :
>>> >
>>> > a = session.query(GeneralBeqReq).filter(GeneralBeqReq.c.BeqReqStatus == 1,
>>> > is_id_valid (GeneralBeqReq.c.id) == True).all()
>>> >
>>> > When I run the above query It is throwing the following error.
>>> >
>>> > AttributeError: Neither 'Column' object nor 'Comparator' object has an
>>> > attribute 'strip'
>>> >
>>> >
>>> > Can you please guide me how to use this function inside my query ?
>>> >
>>> >
>>> > --
>>> > SQLAlchemy -
>>> > The Python SQL Toolkit and Object Relational Mapper
>>> >
>>> > http://www.sqlalchemy.org/
>>> >
>>> > To post example code, please provide an MCVE: Minimal, Complete, and
>>> > Verifiable Example. See http://stackoverflow.com/help/mcve for a full
>>> > description.
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>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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