On Mon, Nov 6, 2017 at 12:37 PM, Tucker Beck <tucker.b...@gmail.com> wrote:
> That fixed it. I'm a bit surprised that passing the type_ argument doesn't
> seem to work. Is that a bug or not how that argument is intended to be used?
This is an unusual case because the array you are passing is empty, so
Postgresql does not have enough information to infer the type, which
usually it would have (or wouldn't need in some cases).
The psql command line shows the difference:
test=# select ARRAY [15];
array
-------
{15}
(1 row)
test=# select ARRAY [];
ERROR: cannot determine type of empty array
LINE 1: select ARRAY [];
^
HINT: Explicitly cast to the desired type, for example ARRAY[]::integer[].
>
> On Friday, November 3, 2017 at 1:52:21 PM UTC-7, Mike Bayer wrote:
>>
>> On Fri, Nov 3, 2017 at 2:42 PM, Tucker Beck <tucke...@gmail.com> wrote:
>> > I'm writing a recursive cte with sqlalchemy, and I want it to aggregate
>> > things in an array as it recurses. However, I'm having trouble
>> > initializing
>> > the 'top' half of the cte with an empty array. I've distilled the
>> > problem
>> > down the the basic problem of including an empty array in an
>> > with_entities
>> > clause. Even when I try to set the type of the array explicitly, the sql
>> > that is produced does not have a type for the emtpy array
>> >
>> > Here's a distilation of the problem causing code:
>> >
>> > from sqlalchemy import *
>> > from sqlalchemy.orm import *
>> > from sqlalchemy.ext.declarative import declarative_base
>> > from sqlalchemy.dialects.postgresql import array
>> >
>> > Base = declarative_base()
>> >
>> > class Dummy(Base):
>> > __tablename__ = 'dummies'
>> > id = Column(Integer, primary_key=True)
>> > name = Column(Text)
>> >
>> >
>> > e = create_engine('postgresql+psycopg2://localhost:5432/local_dev',
>> > echo=False)
>> > Base.metadata.create_all(e)
>> > session = Session(e)
>> >
>> >
>> > session.add(Dummy(name='idiot'))
>> > session.add(Dummy(name='fool'))
>> >
>> >
>> > print(session.query(Dummy).with_entities(
>> > Dummy.id,
>> > Dummy.name,
>> > array([], type_=Integer).label('stuff')
>> > ).all())
>> >
>> > And Here's the error that's being produced:
>> >
>> > /venv:cem/ $ python demo2.py
>> > --- Test with_entities using emtpy array ---
>> > Traceback (most recent call last):
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
>> > line 1182, in _execute_context
>> > context)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/engine/default.py",
>> > line 470, in do_execute
>> > cursor.execute(statement, parameters)
>>
>>
>> > psycopg2.ProgrammingError: cannot determine type of empty array
>> > LINE 1: ...s.id AS dummies_id, dummies.name AS dummies_name, ARRAY[]
>> > AS...
>> > ^
>> > HINT: Explicitly cast to the desired type, for example
>> > ARRAY[]::integer[].
>>
>>
>> the error expresses the solution, which is to CAST:
>>
>> from sqlalchemy import cast
>>
>> expr = cast(array(), ARRAY(Integer))
>>
>>
>> >
>> >
>> > The above exception was the direct cause of the following exception:
>> >
>> > Traceback (most recent call last):
>> > File "demo2.py", line 27, in <module>
>> > array([], type_=Integer).label('stuff')
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/orm/query.py",
>> > line 2703, in all
>> > return list(self)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/orm/query.py",
>> > line 2855, in __iter__
>> > return self._execute_and_instances(context)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/orm/query.py",
>> > line 2878, in _execute_and_instances
>> > result = conn.execute(querycontext.statement, self._params)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
>> > line 945, in execute
>> > return meth(self, multiparams, params)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/sql/elements.py",
>> > line 263, in _execute_on_connection
>> > return connection._execute_clauseelement(self, multiparams, params)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
>> > line 1053, in _execute_clauseelement
>> > compiled_sql, distilled_params
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
>> > line 1189, in _execute_context
>> > context)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
>> > line 1402, in _handle_dbapi_exception
>> > exc_info
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
>> > line 203, in raise_from_cause
>> > reraise(type(exception), exception, tb=exc_tb, cause=cause)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/util/compat.py",
>> > line 186, in reraise
>> > raise value.with_traceback(tb)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/engine/base.py",
>> > line 1182, in _execute_context
>> > context)
>> > File
>> >
>> > "/Users/tbeck/.virtualenvs/cem/lib/python3.5/site-packages/sqlalchemy/engine/default.py",
>> > line 470, in do_execute
>> > cursor.execute(statement, parameters)
>> > sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) cannot
>> > determine type of empty array
>> > LINE 1: ...s.id AS dummies_id, dummies.name AS dummies_name, ARRAY[]
>> > AS...
>> > ^
>> > HINT: Explicitly cast to the desired type, for example
>> > ARRAY[]::integer[].
>> > [SQL: 'SELECT dummies.id AS dummies_id, dummies.name AS dummies_name,
>> > ARRAY[] AS stuff \nFROM dummies']
>> >
>> >
>> > I worked really hard on getting the cte to work (and it does) but now
>> > that
>> > I'm trying to aggregate with it, I'm running into what seems like a
>> > fundamental issue. Any help would be greatly appreciated.
>> >
>> > --
>> > 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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