Okay, perhaps there is another approach?
I got my required behavior with something like
t = Stuff(**kwargs)
t = session.merge(t)
print(t.dict())
session.rollback()
But this causes the db to give t a primary key even though all I would like
is
the associated persistent objects. Unless I can inject the select execution
directly
into the model?
On Thursday, February 2, 2017 at 8:55:06 AM UTC-6, Mike Bayer wrote:
>
>
>
> On 02/02/2017 09:29 AM, Shane Carey wrote:
> > Hi, I have a use case where I need to enable relationship loading on a
> > single object. However, I initialize the foreign key of this
> > relationship using an inline select statement.
> >
> >
> > @event.listens_for(Thing, 'init', propagate=True)
> > def set_identity(instance, *args, **kwargs):
> > mapper = object_mapper(instance)
> > instance.type_id = select([Type.id]).where(Type.type ==
> > mapper.polymorphic_identity)
> >
> >
> > thing = Stuff(text='thing1', stuff='stuff1')
> >
> > s.enable_relationship_loading(thing)
> >
> > print(thing.dict())
> >
> > From the docs, I am fuzzy on whether or not this should be able to work
> > because the relationship loading is enabled on the foreign key
> > which is set here to a select statement. I get the error:
>
> yeah no, that's not going to work. you need to run that SELECT
> statement manually and apply the integer identifier to the
> instance.type_id for this use case.
>
>
>
> >
> > 2017-02-02 08:25:58,789 INFO sqlalchemy.engine.base.Engine SELECT
> > type.id AS type_id, type.type AS type_type
> > FROM type
> > WHERE type.id = %(param_1)s
> > 2017-02-02 08:25:58,789 INFO sqlalchemy.engine.base.Engine {'param_1':
> > <sqlalchemy.sql.selectable.Select at 0x3471b50; Select object>}
> > Traceback (most recent call last):
> > File "sqlalchemy_casc_backref_test.py", line 70, in <module>
> > print(thing.dict())
> > File "sqlalchemy_casc_backref_test.py", line 31, in dict
> > 'type': self.type.type,
> > File "C:\Python35\lib\site-packages\sqlalchemy\orm\attributes.py",
> > line 237, in __get__
> > return self.impl.get(instance_state(instance), dict_)
> > File "C:\Python35\lib\site-packages\sqlalchemy\orm\attributes.py",
> > line 584, in get
> > value = self.callable_(state, passive)
> > File "C:\Python35\lib\site-packages\sqlalchemy\orm\strategies.py",
> > line 560, in _load_for_state
> > return self._emit_lazyload(session, state, ident_key, passive)
> > File "<string>", line 1, in <lambda>
> > File "C:\Python35\lib\site-packages\sqlalchemy\orm\strategies.py",
> > line 606, in _emit_lazyload
> > return loading.load_on_ident(q, ident_key)
> > File "C:\Python35\lib\site-packages\sqlalchemy\orm\loading.py", line
> > 223, in load_on_ident
> > return q.one()
> > File "C:\Python35\lib\site-packages\sqlalchemy\orm\query.py", line
> > 2754, in one
> > ret = self.one_or_none()
> > File "C:\Python35\lib\site-packages\sqlalchemy\orm\query.py", line
> > 2724, in one_or_none
> > ret = list(self)
> > File "C:\Python35\lib\site-packages\sqlalchemy\orm\query.py", line
> > 2795, in __iter__
> > return self._execute_and_instances(context)
> > File "C:\Python35\lib\site-packages\sqlalchemy\orm\query.py", line
> > 2818, in _execute_and_instances
> > result = conn.execute(querycontext.statement, self._params)
> > File "C:\Python35\lib\site-packages\sqlalchemy\engine\base.py", line
> > 945, in execute
> > return meth(self, multiparams, params)
> > File "C:\Python35\lib\site-packages\sqlalchemy\sql\elements.py", line
> > 263, in _execute_on_connection
> > return connection._execute_clauseelement(self, multiparams, params)
> > File "C:\Python35\lib\site-packages\sqlalchemy\engine\base.py", line
> > 1053, in _execute_clauseelement
> > compiled_sql, distilled_params
> > File "C:\Python35\lib\site-packages\sqlalchemy\engine\base.py", line
> > 1189, in _execute_context
> > context)
> > File "C:\Python35\lib\site-packages\sqlalchemy\engine\base.py", line
> > 1396, in _handle_dbapi_exception
> > util.reraise(*exc_info)
> > File "C:\Python35\lib\site-packages\sqlalchemy\util\compat.py", line
> > 186, in reraise
> > raise value
> > File "C:\Python35\lib\site-packages\sqlalchemy\engine\base.py", line
> > 1182, in _execute_context
> > context)
> > File "C:\Python35\lib\site-packages\sqlalchemy\engine\default.py",
> > line 462, in do_execute
> > cursor.execute(statement, parameters)
> > File "C:\Python35\lib\site-packages\pymysql\cursors.py", line 164, in
> > execute
> > query = self.mogrify(query, args)
> > File "C:\Python35\lib\site-packages\pymysql\cursors.py", line 143, in
> > mogrify
> > query = query % self._escape_args(args, conn)
> > File "C:\Python35\lib\site-packages\pymysql\cursors.py", line 123, in
> > _escape_args
> > return dict((key, conn.literal(val)) for (key, val) in args.items())
> > File "C:\Python35\lib\site-packages\pymysql\cursors.py", line 123, in
> > <genexpr>
> > return dict((key, conn.literal(val)) for (key, val) in args.items())
> > File "C:\Python35\lib\site-packages\pymysql\connections.py", line 800,
> > in literal
> > return self.escape(obj, self.encoders)
> > File "C:\Python35\lib\site-packages\pymysql\connections.py", line 793,
> > in escape
> > return escape_item(obj, self.charset, mapping=mapping)
> > File "C:\Python35\lib\site-packages\pymysql\converters.py", line 27,
> > in escape_item
> > val = encoder(val, mapping)
> > File "C:\Python35\lib\site-packages\pymysql\converters.py", line 110,
> > in escape_unicode
> > return u"'%s'" % _escape_unicode(value)
> > File "C:\Python35\lib\site-packages\pymysql\converters.py", line 73,
> > in _escape_unicode
> > return value.translate(_escape_table)
> > AttributeError: 'Select' object has no attribute 'translate'
> >
> > When I assume the orm attempts to load the relationship, by using the
> > select object itself rather than executing it as a subquery or join, as
> > I can see in the first line of the above.
> >
> > --
> > 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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