model_config incorrectly added to RootModel classes with --use-annotated and model configuration flags

[DanielSchaffer]

Describe the bug The generator incorrectly includes a model_config on subclasses of RootModel

To Reproduce You can reproduce with a schema that defines an array type having items with constrained primitive types, and a generator configuration that requires adding model_config and uses the annotated pattern.

Example schema:

{
  "components": {
    "schemas": {
      "MyModel": {
        "type": "object",
        "properties": {
          "theItems": {
            "type": "array",
            "items": {
              "type": "string",
              "maxLength": 140,
              "minLength": 2
            }
          }
        }
      }
    }
  }
}

Which generates:

from typing import Annotated, List, Optional

from pydantic import BaseModel, ConfigDict, Field, RootModel


class TheItem(RootModel[str]):
    model_config = ConfigDict(
        populate_by_name=True,
    )
    root: Annotated[str, Field(max_length=140, min_length=2)]


class MyModel(BaseModel):
    model_config = ConfigDict(
        populate_by_name=True,
    )
    theItems: Optional[List[TheItem]] = None

Used commandline:

datamodel-codegen --input test.json --input-file-type=openapi --output test.py --output-model-type=pydantic_v2.BaseModel --allow-population-by-field-name --use-annotated

Expected behavior RootModel subclasses should not have model_config

Version:

• OS: macOS Sequoia 15.5
• Python version: 3.11
• datamodel-code-generator version: 0.33.0