docs and improvements

Author: the-infinity

docs/05-dataclasses.md

@@ -299,7 +299,7 @@ being applied to the class.
 
 ## Reject unknown fields
 
-Per default, validataclass just ignores any unknown fields in the input dictionary when validating an object.
+By default, validataclass just ignores any unknown fields in the input dictionary when validating an object.
 This makes sense for normal APIs, as additional fields are just filtered out, and it makes validataclass more robust to
 changes in the API. There might be situations where one needs to have a strict validation of additional fields,
 for example, to match an OpenAPI validation.

src/validataclass/dataclasses/validataclass.py

@@ -85,11 +85,27 @@ class ExampleDataclass:
 
     Optional parameters to the decorator will be passed directly to the `@dataclass` decorator. In most cases no
     parameters are necessary. By default, the argument `kw_only=True` will be used for validataclasses.
+
+    Additionally, the following validataclass-specific parameter is supported:
+
+    `reject_unknown_fields`: If set to `True`, the `DataclassValidator` will reject any input fields that are not
+    defined in the validataclass, raising a validation error for each unknown field.
+
+    Example with `reject_unknown_fields`:
+
+    ```
+    @validataclass(reject_unknown_fields=True)
+    class StrictDataclass:
+        example_field1: str = StringValidator()
+    ```
+
+    In this example, validating `{'example_field1': 'cookie', 'unknown': 'value'}` would raise a
+    `DictFieldsValidationError` with an error for the `unknown` field.
     """
 
     def decorator(_cls: type[_T]) -> type[_T]:
         # Pop validataclass-specific options before passing kwargs to @dataclass
-        reject_unknown_fields = kwargs.pop('reject_unknown_fields', False)
+        reject_unknown_fields = kwargs.pop('reject_unknown_fields', None)
 
         # Set kw_only=True as the default to allow required and optional fields in any order
         kwargs.setdefault('kw_only', True)

src/validataclass/validators/dataclass_validator.py

@@ -138,7 +138,7 @@ def __init__(
 
         # Use the explicit parameter if given, otherwise fall back to the dataclass setting
         if reject_unknown_fields is None:
-            reject_unknown_fields = getattr(dataclass_cls, '__reject_unknown_fields__', None)
+            reject_unknown_fields = getattr(dataclass_cls, '__reject_unknown_fields__', False)
         self.field_defaults = {}
 
         # Collect field validators and required fields for the DictValidator by examining the dataclass fields