Support ClassVar for Pydantic v2

Author: ubaumann

src/datamodel_code_generator/model/pydantic_v2/base_model.py

@@ -31,6 +31,7 @@
     IMPORT_VALIDATION_INFO,
     IMPORT_VALIDATOR_FUNCTION_WRAP_HANDLER,
 )
+from datamodel_code_generator.model.imports import IMPORT_CLASSVAR
 from datamodel_code_generator.reference import ModelResolver
 from datamodel_code_generator.types import chain_as_tuple
 from datamodel_code_generator.util import field_validator, model_validate, model_validator
@@ -187,11 +188,21 @@ def _has_discriminator_in_data_type(self) -> bool:
         """Check if any nested DataType has a discriminator."""
         return any(dt.discriminator for dt in self.data_type.all_data_types)
 
+    @property
+    def class_var_type_hint(self) -> str:
+        return f"ClassVar[{self.type_hint}]"
+
+    @property
+    def is_class_var(self) -> bool:
+        return self.extras.get("x-is_classvar") is True
+
     @property
     def imports(self) -> tuple[Import, ...]:
         """Get all required imports including AliasChoices and Field for discriminator."""
         base_imports = super().imports
         extra_imports: list[Import] = []
+        if self.is_class_var:
+            extra_imports.append(IMPORT_CLASSVAR)
         if self.validation_aliases:
             from datamodel_code_generator.model.pydantic_v2.imports import IMPORT_ALIAS_CHOICES  # noqa: PLC0415
 

src/datamodel_code_generator/model/template/pydantic_v2/BaseModel.jinja2

@@ -16,7 +16,9 @@ class {{ class_name }}({{ base_class }}):{% if comment is defined %}  # {{ comme
 {%- endfilter %}
 {%- endif %}
 {%- for field in fields %}
-    {%- if not field.annotated and field.field %}
+    {%- if field.is_class_var and field.represented_default %}
+    {{ field.name }}: {{ field.class_var_type_hint }} = {{ field.represented_default }}
+    {%- elif not field.annotated and field.field %}
     {{ field.name }}: {{ field.type_hint }} = {{ field.field }}
     {%- else %}
     {%- if field.annotated %}

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

@@ -0,0 +1,13 @@
+# generated by datamodel-codegen:
+#   filename:  has_classvar_extra.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import ClassVar
+
+from pydantic import BaseModel, Field
+
+
+class Model(BaseModel):
+    namespace: ClassVar[str | None] = 'test'

tests/data/jsonschema/has_classvar_extra.json

@@ -0,0 +1,10 @@
+{
+    "type": "object",
+    "properties": {
+        "namespace": {
+            "type": "string",
+            "x-is_classvar": true,
+            "default": "test"
+        }
+    }
+}

tests/main/jsonschema/test_main_jsonschema.py

@@ -7903,3 +7903,15 @@ def test_validators_requires_pydantic_v2(output_file: Path, tmp_path: Path, caps
         capsys=capsys,
         expected_stderr_contains="--validators option requires Pydantic v2",
     )
+
+
+def test_jsonschema_classvar_extra_pydantic_v2(output_file: Path) -> None:
+    """Test default value handling."""
+    run_main_and_assert(
+        input_path=JSON_SCHEMA_DATA_PATH / "has_classvar_extra.json",
+        output_path=output_file,
+        input_file_type="jsonschema",
+        assert_func=assert_file_content,
+        expected_file="has_classvar_extra.py",
+        extra_args=["--output-model-type", "pydantic_v2.BaseModel", "--field-include-all-keys"],
+    )