Sourced from datamodel-code-generator's releases.

0.53.0

Breaking Changes

Custom Template Update Required

• Parser subclass signature change - The Parser base class now requires two generic type parameters: Parser[ParserConfigT, SchemaFeaturesT] instead of just Parser[ParserConfigT]. Custom parser subclasses must be updated to include the second type parameter. (#2929)

  # Before
  class MyCustomParser(Parser["MyParserConfig"]):
      ...
  # After
  class MyCustomParser(Parser["MyParserConfig", "JsonSchemaFeatures"]):
      ...
  

• New abstract schema_features property required - Custom parser subclasses must now implement the schema_features abstract property that returns a JsonSchemaFeatures (or subclass) instance. (#2929)

  from functools import cached_property
  from datamodel_code_generator.parser.schema_version import JsonSchemaFeatures
  from datamodel_code_generator.enums import JsonSchemaVersion
  class MyCustomParser(Parser["MyParserConfig", "JsonSchemaFeatures"]):
      @cached_property
      def schema_features(self) -> JsonSchemaFeatures:
          return JsonSchemaFeatures.from_version(JsonSchemaVersion.Draft202012)
  

• Parser _create_default_config refactored to use class variable - Subclasses that override _create_default_config should now set the _config_class_name class variable instead. The base implementation uses this variable to dynamically instantiate the correct config class. (#2929)

  # Before
  @classmethod
  def _create_default_config(cls, options: MyConfigDict) -> MyParserConfig:
      # custom implementation...
  # After
  _config_class_name: ClassVar[str] = "MyParserConfig"
  # No need to override _create_default_config if using standard config creation
  

• Template condition for default values changed - If you use custom Jinja2 templates based on BaseModel_root.jinja2 or RootModel.jinja2, the condition for including default values has changed from field.required to (field.required and not field.has_default). Update your custom templates if you override these files. (#2960)

Code Generation Changes

• RootModel default values now included in generated code - Previously, default values defined in JSON Schema or OpenAPI specifications for root models were not being applied to the generated Pydantic code. Now these defaults are correctly included. For example, a schema defining a root model with default: 1 will generate __root__: int = 1 (Pydantic v1) or root: int = 1 (Pydantic v2) instead of just __root__: int or root: int. This may affect code that relied on the previous behavior where RootModel fields had no default values. (#2960)
• Required fields with list defaults now use default_factory - Previously, required fields with list-type defaults (like __root__: list[ID] = ['abc', 'efg']) were generated with direct list assignments. Now they correctly use Field(default_factory=lambda: ...) which follows Python best practices for mutable defaults. This changes the structure of generated code for root models and similar patterns with list defaults. (#2958) Before:

  class Family(BaseModel):
      __root__: list[ID] = ['abc', 'efg']
  

  After:

  class Family(BaseModel):
  

... (truncated)

Sourced from datamodel-code-generator's changelog.

0.53.0 - 2026-01-12

Breaking Changes

Custom Template Update Required

• Parser subclass signature change - The Parser base class now requires two generic type parameters: Parser[ParserConfigT, SchemaFeaturesT] instead of just Parser[ParserConfigT]. Custom parser subclasses must be updated to include the second type parameter. (#2929)

  # Before
  class MyCustomParser(Parser["MyParserConfig"]):
      ...
  # After
  class MyCustomParser(Parser["MyParserConfig", "JsonSchemaFeatures"]):
      ...
  

• New abstract schema_features property required - Custom parser subclasses must now implement the schema_features abstract property that returns a JsonSchemaFeatures (or subclass) instance. (#2929)

  from functools import cached_property
  from datamodel_code_generator.parser.schema_version import JsonSchemaFeatures
  from datamodel_code_generator.enums import JsonSchemaVersion
  class MyCustomParser(Parser["MyParserConfig", "JsonSchemaFeatures"]):
      @cached_property
      def schema_features(self) -> JsonSchemaFeatures:
          return JsonSchemaFeatures.from_version(JsonSchemaVersion.Draft202012)
  

• Parser _create_default_config refactored to use class variable - Subclasses that override _create_default_config should now set the _config_class_name class variable instead. The base implementation uses this variable to dynamically instantiate the correct config class. (#2929)

  # Before
  @classmethod
  def _create_default_config(cls, options: MyConfigDict) -> MyParserConfig:
      # custom implementation...
  # After
  _config_class_name: ClassVar[str] = "MyParserConfig"
  # No need to override _create_default_config if using standard config creation
  

• Template condition for default values changed - If you use custom Jinja2 templates based on BaseModel_root.jinja2 or RootModel.jinja2, the condition for including default values has changed from field.required to (field.required and not field.has_default). Update your custom templates if you override these files. (#2960)

Code Generation Changes

• RootModel default values now included in generated code - Previously, default values defined in JSON Schema or OpenAPI specifications for root models were not being applied to the generated Pydantic code. Now these defaults are correctly included. For example, a schema defining a root model with default: 1 will generate __root__: int = 1 (Pydantic v1) or root: int = 1 (Pydantic v2) instead of just __root__: int or root: int. This may affect code that relied on the previous behavior where RootModel fields had no default values. (#2960)
• Required fields with list defaults now use default_factory - Previously, required fields with list-type defaults (like __root__: list[ID] = ['abc', 'efg']) were generated with direct list assignments. Now they correctly use Field(default_factory=lambda: ...) which follows Python best practices for mutable defaults. This changes the structure of generated code for root models and similar patterns with list defaults. (#2958) Before:

  class Family(BaseModel):
      __root__: list[ID] = ['abc', 'efg']
  

  After:

... (truncated)

• a6a7b04 Fix bug in handling of graphql empty list defaults (#2948)
• 838b2a0 Fix array RootModel default value handling in parser (#2963)
• e717208 Fix allOf array property merging to preserve child $ref (#2962)
• ae89a00 Add GenerateConfig lazy import from top-level module (#2961)
• 88c7fe4 Fix required list fields ignoring empty default values (#2958)
• 4cbf3bf Fix RootModel default value not being applied (#2960)
• aa088d6 Add --use-closed-typed-dict option to control PEP 728 TypedDict generation (#...
• 98f3a48 Fix IndexError when using --reuse-scope=tree with single file output (#2954)
• fa1fc11 fix: move UnionMode import outside TYPE_CHECKING for Pydantic runtime… (#2950)
• 4decf36 Add comprehensive feature metadata to schema version dataclasses (#2946)
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