if you use 1.4 /2.0 querying style you can call upon the scalars() method of
the result
result = session.execute(select(MyClass.attr))
elements = result.scalars().all()
or
result = session.scalars(select(...))
elements = result.all()
otherwise you can just iterate like this:
elements = [e for e, in sess.query(MyClass.attr)]
On Wed, Nov 10, 2021, at 3:22 PM, niuji...@gmail.com wrote:
> This is very helpful.
>
> How to return a list of scalar values in this case? Now the query returns a
> list of tuples, and each tuple only has one value, which is what actually
> needed. Is there a parameter to return a series of scalar value like this?
> On Wednesday, November 10, 2021 at 12:05:27 PM UTC-8 Mike Bayer wrote:
>> __
>> it has to do with how SQLAlchemy determines the FROM list in a select()
>> statement.
>>
>> if you say select(table.c.id), it knows that "table" is the thing to select
>> "from".
>>
>> however, if you say select(select(...).correlate(...).scalar_subquery()),
>> that's assuming it's a SELECT from a scalar subquery, which normally does
>> not imply a FROM clause.
>>
>> In this case, that you are saying correlate(C), we could argue that *does*
>> imply a FROM clause of some kind, but SQLAlchemy doesn't make that leap
>> right now. You might have said correlate(C, D) or correlate_except(Q) and
>> then it's not as clear what the scalar subquery would be selected FROM.
>>
>> going further, there *could* be some new kind of API where a scalar subquery
>> could suggest a FROM clause that should be used when this subquery is
>> selected FROM. that would allow your column_property() to be built up such
>> that it would be "self sufficient" when queried by itself. but again we
>> don't have that right now.
>>
>> with all those options exhausted, for SQLAlchemy to be given
>> select(select().scalar_subquery()), and then to produce "SELECT * FROM
>> (SELECT ....) FROM <some table>", that FROM part has to be added on
>> explicitly, i.e. select(select().scalar_subuqery()).select_from(<some
>> table>).
>>
>>
>>
>> On Wed, Nov 10, 2021, at 2:35 PM, niuji...@gmail.com wrote:
>>> This works! Could you explain a little about this differences by using
>>> select_from here? I think this is very important and useful, really want to
>>> learn it right.
>>>
>>> On Wednesday, November 10, 2021 at 5:55:44 AM UTC-8 Mike Bayer wrote:
>>>> __
>>>> try calling:
>>>>
>>>> query(C.symbol_from_a).select_from(C)
>>>>
>>>>
>>>>
>>>> On Wed, Nov 10, 2021, at 4:50 AM, niuji...@gmail.com wrote:
>>>>> class A(Base):
>>>>> primary_id = Column(Integer, prirmary_key=True)
>>>>> some_A_marker = Column(String)
>>>>>
>>>>> class B(Base):
>>>>> primary_id = Column(Integer, primary_key=True)
>>>>> referencing_A_id = Column(Integer, ForeignKey(A.primary_id))
>>>>>
>>>>> class C(Base):
>>>>> primary_id = Column(Integer, primary_key=True)
>>>>> basedOn_B_id = Column(Integer, ForeignKey(B.primary_id))
>>>>> symbol_from_A = column_property(
>>>>>
>>>>> sasql.select(A.some_A_marker).select_from(A).join(B).where(B.primary_id
>>>>> == C.basedOn_B_id).correlate(C).scalar_subquery().label("symbol_from_A")
>>>>> )
>>>>>
>>>>>
>>>>> When I query this highlighted column_property along with the whole
>>>>> object, it works fine:
>>>>>
>>>>> >>> sess.query(C, C.symbol_from_A).all()
>>>>>
>>>>> However, when I query this column_property alone, it doesn't work:
>>>>>
>>>>> >>>sess.query(C.symbol_from_A).distinct().all()
>>>>>
>>>>> I noticed that somehow the correlated subquery wasn't executed property
>>>>> when query that column_property independently.
>>>>>
>>>>> How to solve this?
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> 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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>>>>>
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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
>>> 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
> 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 description.
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