Pydantic error using cos_agent in a machine charm

[erik78se]

I'm going through some code I've made some time ago to test the COS lite with machine charms.

https://github.com/erik78se/juju-operators-examples/tree/main/observed

After upgrading a previous build charm, using the cos_agent interface https://canonical.github.io/charm-relation-interfaces/interfaces/cos_agent/v0/

I strike an ERROR in the upgrade-hook.

unit-observed-1: 16:44:51 WARNING unit.observed/1.upgrade-charm If you got this error by calling handler() within __get_pydantic_core_schema__ then you likely need to call handler.generate_schema(<some type>) since we do not call __get_pydantic_core_schema__ on <some type> otherwise to avoid infinite recursion.

Is this an error or am I doing something wrong?

[erik78se]

Also, in the error logs there is this message:

"unit-observed-1: 17:04:08 WARNING unit.observed/1.upgrade-charm pydantic.errors.PydanticSchemaGenerationError: Unable to generate pydantic-core schema for <class 'cosl.grafana_dashboard.GrafanaDashboard'>. Set arbitrary_types_allowed=True in the model_config to ignore this error or implement __get_pydantic_core_schema__ on your type to fully support it."

I set the suggested value:

juju model-config arbitrary_types_allowed=true
juju resolved observed/0

But there is no resolution to the error.

[erik78se]

Possibly, this is due to some of my grafana-dashboards not being "correct" ?

unit-observed-2: 17:33:11 WARNING unit.observed/2.install return self._model_schema(obj)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 580, in _model_schema
unit-observed-2: 17:33:11 WARNING unit.observed/2.install {k: self._generate_md_field_schema(k, v, decorators) for k, v in fields.items()},
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 580, in
unit-observed-2: 17:33:11 WARNING unit.observed/2.install {k: self._generate_md_field_schema(k, v, decorators) for k, v in fields.items()},
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 916, in _generate_md_field_schema
unit-observed-2: 17:33:11 WARNING unit.observed/2.install common_field = self._common_field_schema(name, field_info, decorators)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 1081, in _common_field_schema
unit-observed-2: 17:33:11 WARNING unit.observed/2.install schema = self._apply_annotations(
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 1820, in _apply_annotations
unit-observed-2: 17:33:11 WARNING unit.observed/2.install schema = get_inner_schema(source_type)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_schema_generation_shared.py", line 82, in call
unit-observed-2: 17:33:11 WARNING unit.observed/2.install schema = self._handler(source_type)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 1902, in new_handler
unit-observed-2: 17:33:11 WARNING unit.observed/2.install schema = metadata_get_schema(source, get_inner_schema)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_std_types_schema.py", line 314, in get_pydantic_core_schema
unit-observed-2: 17:33:11 WARNING unit.observed/2.install items_schema = handler.generate_schema(self.item_source_type)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_schema_generation_shared.py", line 96, in generate_schema
unit-observed-2: 17:33:11 WARNING unit.observed/2.install return self._generate_schema.generate_schema(source_type)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 502, in generate_schema
unit-observed-2: 17:33:11 WARNING unit.observed/2.install schema = self._generate_schema_inner(obj)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 758, in _generate_schema_inner
unit-observed-2: 17:33:11 WARNING unit.observed/2.install return self.match_type(obj)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 844, in match_type
unit-observed-2: 17:33:11 WARNING unit.observed/2.install return self._unknown_type_schema(obj)
unit-observed-2: 17:33:11 WARNING unit.observed/2.install File "/var/lib/juju/agents/unit-observed-2/charm/venv/pydantic/_internal/_generate_schema.py", line 405, in _unknown_type_schema
unit-observed-2: 17:33:11 WARNING unit.observed/2.install raise PydanticSchemaGenerationError(
unit-observed-2: 17:33:11 WARNING unit.observed/2.install pydantic.errors.PydanticSchemaGenerationError: Unable to generate pydantic-core schema for <class 'cosl.grafana_dashboard.GrafanaDashboard'>. Set arbitrary_types_allowed=True in the model_config to ignore this error or implement __get_pydantic_core_schema__ on your type to fully support it.
unit-observed-2: 17:33:11 WARNING unit.observed/2.install
unit-observed-2: 17:33:11 WARNING unit.observed/2.install If you got this error by calling handler() within __get_pydantic_core_schema__ then you likely need to call handler.generate_schema(<some type>) since we do not call __get_pydantic_core_schema__ on <some type> otherwise to avoid infinite recursion.
unit-observed-2: 17:33:11 WARNING unit.observed/2.install
unit-observed-2: 17:33:11 WARNING unit.observed/2.install For further information visit https://errors.pydantic.dev/2.7/u/schema-for-unknown-type
unit-observed-2: 17:33:11 ERROR juju.worker.uniter.operation hook "install" (via hook dispatching script: dispatch) failed: exit status 1
unit-observed-2: 17:33:11 INFO juju.worker.uniter awaiting error resolution for "install" hook

[erik78se]

I have found the issue resolution, which is that the requirements.txt for python needs to be pinning pydantic to < 2.

This is important information and even more important to perhaps get a fix for since this will hit anyone trying to use the lib.