Thank you Mike! My event-hooking code is like this:
@sqlalchemy.event.listens_for(_MyBase, "class_instrument")
def set_serialize_map(cls):
module_logger.info(
f"<set_serialize_map> for {cls.__name__} is just invoked!")
...
Here is the stack trace:
2021-10-10 03:47:34 AM database MainThread 140107141936960 INFO
<set_serialize_map> for GeoAreaVariantName is just invoked!
Traceback (most recent call last):
File "main.py", line 101, in <module>
cherrypy.quickstart(root=HomePage_Server(),
File "main.py", line 50, in __init__
self._collect_subunit_servers()
File "main.py", line 73, in _collect_subunit_servers
unit_server = importlib.import_module(
File "/usr/lib/python3.8/importlib/__init__.py", line 127, in
import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
File "<frozen importlib._bootstrap>", line 991, in _find_and_load
File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
File "<frozen importlib._bootstrap_external>", line 848, in exec_module
File "<frozen importlib._bootstrap>", line 219, in
_call_with_frames_removed
File "/codebase_mountpoint/codebase/geography_server.py", line 14, in
<module>
from database.geography_schema import *
File "/codebase_mountpoint/codebase/database/geography_schema.py", line
19, in <module>
class GeoArea(my_mixins.HasVariantName_Mixin, dal.Base):
File "/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_api.py",
line 72, in __init__
_as_declarative(reg, cls, dict_)
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_base.py", line
126, in _as_declarative
return _MapperConfig.setup_mapping(registry, cls, dict_, None, {})
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_base.py", line
177, in setup_mapping
return cfg_cls(registry, cls_, dict_, table, mapper_kw)
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_base.py", line
299, in __init__
self._scan_attributes()
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_base.py", line
557, in _scan_attributes
ret = getattr(cls, name)
File "/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_api.py",
line 237, in __get__
reg[desc] = obj = desc.fget(cls)
File "/codebase_mountpoint/codebase/database/my_mixins.py", line 39, in
variant_names
cls.VariantName = type(
File "/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_api.py",
line 72, in __init__
_as_declarative(reg, cls, dict_)
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_base.py", line
126, in _as_declarative
return _MapperConfig.setup_mapping(registry, cls, dict_, None, {})
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_base.py", line
177, in setup_mapping
return cfg_cls(registry, cls_, dict_, table, mapper_kw)
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_base.py", line
314, in __init__
self._early_mapping(mapper_kw)
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_base.py", line
200, in _early_mapping
self.map(mapper_kw)
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/decl_base.py", line
992, in map
mapper_cls(self.cls, self.local_table, **self.mapper_args),
File "<string>", line 2, in __init__
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/util/deprecations.py",
line 298, in warned
return fn(*args, **kwargs)
File "/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/mapper.py",
line 682, in __init__
self._configure_class_instrumentation()
File "/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/mapper.py",
line 1228, in _configure_class_instrumentation
manager = instrumentation.register_class(
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/instrumentation.py",
line 574, in register_class
manager._update_state(
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/instrumentation.py",
line 154, in _update_state
self._finalize()
File
"/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/instrumentation.py",
line 163, in _finalize
_instrumentation_factory.dispatch.class_instrument(self.class_)
File "/usr/local/lib/python3.8/dist-packages/sqlalchemy/event/attr.py",
line 343, in __call__
fn(*args, **kw)
File "/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/events.py",
line 79, in listen
return fn(target_cls, *arg)
File "/codebase_mountpoint/codebase/database/__init__.py", line 177, in
set_serialize_map
for c in visible_table_columns:
File "/codebase_mountpoint/codebase/database/__init__.py", line 175, in
<lambda>
lambda x: cls.get_property_name_from_column(x) not in negatives,
File "/codebase_mountpoint/codebase/database/__init__.py", line 106, in
get_property_name_from_column
return sqlalchemy.inspect(cls).get_property_by_column(column_obj).key
File "/usr/local/lib/python3.8/dist-packages/sqlalchemy/orm/mapper.py",
line 1998, in get_property_by_column
return self._columntoproperty[column]
AttributeError: 'Mapper' object has no attribute '_columntoproperty'
On Friday, October 8, 2021 at 2:12:14 PM UTC-7 Mike Bayer wrote:
>
>
> On Fri, Oct 8, 2021, at 4:13 PM, niuji...@gmail.com wrote:
>
> Thanks for this very important information!
>
> If I do want to utilize the mapper functions at this stage, what can I do?
> currently I have this error showing up:
>
> AttributeError: 'Mapper' object has no attribute '_columntoproperty'
>
>
> you would need to show me a stack trace on that. however, depending on
> which event you are using to get at the mapper, it may not be initialized
> yet (can confirm that class_instrument() event is too early if access to
> the internals of the mapper is required). as stated previously, the
> best event to use when a class is first mapped but before the full span of
> mappings have been considered is the before_mapper_configured() event (can
> confirm _columntoproperty is available at that stage).
>
>
>
> On Friday, October 8, 2021 at 6:58:02 AM UTC-7 Mike Bayer wrote:
>
>
>
> On Fri, Oct 8, 2021, at 7:09 AM, niuji...@gmail.com wrote:
>
> In order to make sure that the mapped class is fully ready, I chose the
> latest point, namely `class_instrument`.
> However, it seems that at that moment the `__mapper__` attribute is not
> available.
> When I tried
> return cls.__mapper__.get_property_by_column(column_obj).key
>
> I got:
> AttributeError: type object 'GeoAreaVariantName' has no attribute
> '__mapper__'
>
> Is this a bug or a feature?
>
>
> it's a normal behavior, that event is called before mapping has been
> established.
>
> but also, the "__mapper__" attribute is a convenience feature that should
> not be relied upon at this stage. the correct way to get the mapper for a
> class is to use the sqlalchemy.inspect() function, i.e. mapper =
> inspect(class).
>
>
>
>
>
> On Wednesday, October 6, 2021 at 5:36:22 AM UTC-7 Mike Bayer wrote:
>
>
> events that occur around this time include
>
> this one claims it's before:
>
>
> https://docs.sqlalchemy.org/en/14/orm/events.html#sqlalchemy.orm.MapperEvents.instrument_class
>
> this one says after:
>
>
> https://docs.sqlalchemy.org/en/14/orm/events.html#sqlalchemy.orm.InstrumentationEvents.class_instrument
>
> this one is definitely after and is usually fine for anything that needs
> to happen for mapped classes before they are reconciled against other
> classes:
>
>
> https://docs.sqlalchemy.org/en/14/orm/events.html#sqlalchemy.orm.MapperEvents.before_mapper_configured
>
>
> On Wed, Oct 6, 2021, at 4:48 AM, niuji...@gmail.com wrote:
>
> I want to do some after processing on each class that is just put into
> the class_registry. Is there a event hook for 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
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>
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>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
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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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