Django models code identical for postgres JSONField and sqlite TextField

django-models-cross-db-json-fields.py

## AUTHOR: Andrei Anton
## LICENSE: MIT

## USAGE EXAMPLE:
# @model_with_json_fields
# class MyThing(models.Model):
#     JSON_FIELDS = (
#         ['data', dict(default=dict, blank=True)],
#         ['errors', dict(null=True, blank=True)],
#     )
#     ...

def model_with_json_fields(klass):
    """
    Django model class decorator for adding json fields that are implemented as Postgres native JSONField when using postgres and as text fields with (de)serializing getters and setters on other DBs.

    NOTE: when text fields are used, their column names get the '_str' suffix to not clash with the setters/getters

    IMPORTANT: it's your job to tweak the migrations code, using `connection.vendor == 'postgresql'` in migrations to switch field types between django.contrib.postgres.fields.jsonb.JSONField and django.db.models.TextField

    RATIONALE: all other more full-featured solutions for this problem are un-maintained and over-engineered / too heavy to timely debug - this requires some manual setup (migrations) and looks uglier, but has the advantage of simplicity
    """
    for fld_name, ctor_args in klass.JSON_FIELDS:
        if connection.vendor == 'postgresql':
            # native postgres json field
            JSONField(**ctor_args).contribute_to_class(klass, fld_name)
        else:
            # plain text field
            str_fld_name = fld_name + '_str'
            text_fld_ctor_args = ctor_args.copy()
            if ctor_args.get('default', None) is dict:
                text_fld_ctor_args['default'] = '{}'
            elif ctor_args.get('default', None) is list:
                text_fld_ctor_args['default'] = '[]'
            models.TextField(**text_fld_ctor_args).contribute_to_class(klass, str_fld_name)
            # but with property getter/setter (de)serializing to/from json
            def getter(self):
                return json.loads(getattr(self, str_fld_name))
            prop_getter = property(getter)
            def setter(self, val):
                setattr(self, str_fld_name, json.dumps(val))
            prop_getter_setter = prop_getter.setter(setter)
            setattr(klass, fld_name, prop_getter_setter)
    return klass