Fix --allow-population-by-field-name for pydantic v2 dataclass output (#3013)

* Fix --allow-population-by-field-name for pydantic v2 dataclass output (#3010)

DataClass.__init__ never read allow_population_by_field_name from
extra_template_data, so the flag was silently ignored for
pydantic_v2.dataclass output. Add _CONFIG_ATTRIBUTES processing
(matching the BaseModel pattern) to emit populate_by_name in
ConfigDict, with validate_by_name support for --target-pydantic-version 2.11.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Add test for V2.11 validate_by_name path to fix coverage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: butvinm

src/datamodel_code_generator/model/pydantic_v2/dataclass.py

@@ -10,7 +10,7 @@
 from datamodel_code_generator.model import DataModel, DataModelFieldBase
 from datamodel_code_generator.model.base import UNDEFINED
 from datamodel_code_generator.model.dataclass import has_field_assignment
-from datamodel_code_generator.model.pydantic_v2.base_model import Constraints
+from datamodel_code_generator.model.pydantic_v2.base_model import ConfigAttribute, Constraints
 from datamodel_code_generator.model.pydantic_v2.base_model import (
     DataModelField as DataModelFieldV2,
 )
@@ -35,6 +35,17 @@ class DataClass(DataModel):
     DEFAULT_IMPORTS: ClassVar[tuple[Import, ...]] = (IMPORT_PYDANTIC_DATACLASS,)
     SUPPORTS_DISCRIMINATOR: ClassVar[bool] = True
     SUPPORTS_KW_ONLY: ClassVar[bool] = True
+    # frozen/allow_mutation are handled as dataclass decorator arguments, not ConfigDict
+    _CONFIG_ATTRIBUTES_V2: ClassVar[list[ConfigAttribute]] = [
+        ConfigAttribute("allow_population_by_field_name", "populate_by_name", False),  # noqa: FBT003
+        ConfigAttribute("populate_by_name", "populate_by_name", False),  # noqa: FBT003
+        ConfigAttribute("use_attribute_docstrings", "use_attribute_docstrings", False),  # noqa: FBT003
+    ]
+    _CONFIG_ATTRIBUTES_V2_11: ClassVar[list[ConfigAttribute]] = [
+        ConfigAttribute("allow_population_by_field_name", "validate_by_name", False),  # noqa: FBT003
+        ConfigAttribute("populate_by_name", "validate_by_name", False),  # noqa: FBT003
+        ConfigAttribute("use_attribute_docstrings", "use_attribute_docstrings", False),  # noqa: FBT003
+    ]
 
     def __init__(  # noqa: PLR0913
         self,
@@ -90,8 +101,12 @@ def __init__(  # noqa: PLR0913
         if extra:
             config_parameters["extra"] = extra
 
-        if self.extra_template_data.get("use_attribute_docstrings"):
-            config_parameters["use_attribute_docstrings"] = True
+        config_attributes = self._get_config_attributes()
+        for from_, to, invert in config_attributes:
+            if from_ in self.extra_template_data:
+                config_parameters[to] = (
+                    not self.extra_template_data[from_] if invert else self.extra_template_data[from_]
+                )
 
         for data_type in self.all_data_types:
             if data_type.is_custom_type:  # pragma: no cover
@@ -102,6 +117,15 @@ def __init__(  # noqa: PLR0913
             self._additional_imports.append(IMPORT_CONFIG_DICT)
             self.extra_template_data["config"] = config_parameters
 
+    def _get_config_attributes(self) -> list[ConfigAttribute]:
+        """Get config attributes based on target Pydantic version."""
+        from datamodel_code_generator import TargetPydanticVersion  # noqa: PLC0415
+
+        target_version = self.extra_template_data.get("target_pydantic_version")
+        if target_version == TargetPydanticVersion.V2_11:
+            return self._CONFIG_ATTRIBUTES_V2_11
+        return self._CONFIG_ATTRIBUTES_V2
+
     def _get_config_extra(self) -> str | None:
         """Get extra field configuration for ConfigDict."""
         additional_properties = self.extra_template_data.get("additionalProperties")

tests/data/expected/main/jsonschema/pydantic_v2_dataclass_populate_by_name.py

@@ -0,0 +1,13 @@
+# generated by datamodel-codegen:
+#   filename:  simple_string.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from pydantic import ConfigDict
+from pydantic.dataclasses import dataclass
+
+
+@dataclass(config=ConfigDict(populate_by_name=True))
+class Model:
+    s: str

tests/data/expected/main/jsonschema/pydantic_v2_dataclass_validate_by_name.py

@@ -0,0 +1,13 @@
+# generated by datamodel-codegen:
+#   filename:  simple_string.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from pydantic import ConfigDict
+from pydantic.dataclasses import dataclass
+
+
+@dataclass(config=ConfigDict(validate_by_name=True))
+class Model:
+    s: str

tests/main/jsonschema/test_main_jsonschema.py

@@ -18,6 +18,7 @@
     InputFileType,
     PythonVersion,
     PythonVersionMin,
+    TargetPydanticVersion,
     chdir,
     generate,
 )
@@ -1844,6 +1845,39 @@ def test_main_generate_pydantic_v2_dataclass_use_attribute_docstrings(tmp_path:
     assert_file_content(output_file, "pydantic_v2_dataclass_use_attribute_docstrings.py")
 
 
+def test_main_generate_pydantic_v2_dataclass_allow_population_by_field_name(tmp_path: Path) -> None:
+    """Test pydantic_v2.dataclass with allow_population_by_field_name."""
+    output_file: Path = tmp_path / "output.py"
+    input_ = (JSON_SCHEMA_DATA_PATH / "simple_string.json").relative_to(Path.cwd())
+    assert not input_.is_absolute()
+    generate(
+        input_=input_,
+        input_file_type=InputFileType.JsonSchema,
+        output=output_file,
+        output_model_type=DataModelType.PydanticV2Dataclass,
+        allow_population_by_field_name=True,
+    )
+
+    assert_file_content(output_file, "pydantic_v2_dataclass_populate_by_name.py")
+
+
+def test_main_generate_pydantic_v2_dataclass_allow_population_by_field_name_v2_11(tmp_path: Path) -> None:
+    """Test pydantic_v2.dataclass with allow_population_by_field_name and target v2.11."""
+    output_file: Path = tmp_path / "output.py"
+    input_ = (JSON_SCHEMA_DATA_PATH / "simple_string.json").relative_to(Path.cwd())
+    assert not input_.is_absolute()
+    generate(
+        input_=input_,
+        input_file_type=InputFileType.JsonSchema,
+        output=output_file,
+        output_model_type=DataModelType.PydanticV2Dataclass,
+        allow_population_by_field_name=True,
+        target_pydantic_version=TargetPydanticVersion.V2_11,
+    )
+
+    assert_file_content(output_file, "pydantic_v2_dataclass_validate_by_name.py")
+
+
 def test_main_generate_pydantic_v2_dataclass_extra_allow(tmp_path: Path) -> None:
     """Test pydantic_v2.dataclass with extra='allow'."""
     output_file: Path = tmp_path / "output.py"