Support inheritance of multiple custom models

[mtene]

Is your feature request related to a problem? Please describe.
In my scenario, I need to generate models that may have multiple inheritance between each other.
customBasePath nicely takes care of the import and inheritance for a single base class.

Describe the solution you'd like
There are multiple ways to achieve this, in order of (personal) preference:

• allow customTypePath under allOf. This would enable code reuse, as it is already treated as an alternative to type. It might also increase confusion on when to use customTypePath vs customBasePath, as they (now) serve a similar purpose.
• make customBasePath also accept List[str] instead of just str. This will need backwards compatibility and also the name is not suggestive (singular).
• introduce a new custom keyword customBasePaths, the list counterpart of customBasePath. Makes it confusing when both are specified and/or together with allOf.

Describe alternatives you've considered
Currently, I work around this using custom_template_dir and additional_imports.

# src/generate.py
from collections import defaultdict
from pathlib import Path
import datamodel_code_generator

additional_imports = ['mymodule.mybaseclass1.MyBaseClass1', 'mymodule.mybaseclass2.MyBaseClass2']
extra_template_data = defaultdict(dict)
extra_template_data['MySubClass'] = [additional_import.split('.')[-1] for additional_import in additional_imports]

datamodel_code_generator.generate(...,
  custom_template_dir=Path(__file__).parent,
  extra_template_data=extra_template_data,
  additional_imports=additional_imports,
)

{# src/pydantic_v2/BaseModel.jinja2 #}
{% set bases = [] %}
{% if base_classes %}{% set bases = bases + base_classes %}{% endif %}
{% if extra_base_classes %}{% set bases = bases + extra_base_classes %}{% endif %}
{% if bases|length == 0 or base_class != "BaseModel" %}{% set bases = bases + [base_class] %}{% endif %}

{# if this is just going to be `class Foo(Bar): pass`, then might as well just make Foo
an alias for Bar: every pydantic model class consumes considerable memory. #}

{% if bases|length == 1 and not fields and not config %}

{{ class_name }} = {{ bases[0] }}

{% else -%}

{% for decorator in decorators -%}
{{ decorator }}
{% endfor -%}
class {{ class_name }}({{ bases|join(', ') }}):{% if comment is defined %}  # {{ comment }}{% endif %}
...

[mtene]

An alternative could be to allow customBasePath or customTypePath entries under allOf. This sounds cleaner than introducing yet another custom keyword. The latter would also enable code reuse, as it is already treated as an alternative to type.
LE: updated description with this.

[github-actions]

🎉 Released in 0.52.2

The fix/feature from PR #2916 has been included in this release. See the release notes for details.

Thank you for your contribution!