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 <http://type.id> AS type_id, type.type AS type_type
> FROM type
> WHERE type.id <http://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
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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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