Improving the alias configuration API for validation and serialization

python/pydantic_core/_pydantic_core.pyi

@@ -97,6 +97,8 @@ class SchemaValidator:
         context: Any | None = None,
         self_instance: Any | None = None,
         allow_partial: bool | Literal['off', 'on', 'trailing-strings'] = False,
+        by_alias: bool | None = None,
+        by_name: bool | None = None,
     ) -> Any:
         """
         Validate a Python object against the schema and return the validated object.
@@ -114,6 +116,8 @@ class SchemaValidator:
             allow_partial: Whether to allow partial validation; if `True` errors in the last element of sequences
                 and mappings are ignored.
                 `'trailing-strings'` means any final unfinished JSON string is included in the result.
+            by_alias: Whether to use the field's alias to match the input data to an attribute.
+            by_name: Whether to use the field's name to match the input data to an attribute.
 
         Raises:
             ValidationError: If validation fails.
@@ -130,6 +134,8 @@ class SchemaValidator:
         from_attributes: bool | None = None,
         context: Any | None = None,
         self_instance: Any | None = None,
+        by_alias: bool | None = None,
+        by_name: bool | None = None,
     ) -> bool:
         """
         Similar to [`validate_python()`][pydantic_core.SchemaValidator.validate_python] but returns a boolean.
@@ -148,6 +154,8 @@ class SchemaValidator:
         context: Any | None = None,
         self_instance: Any | None = None,
         allow_partial: bool | Literal['off', 'on', 'trailing-strings'] = False,
+        by_alias: bool | None = None,
+        by_name: bool | None = None,
     ) -> Any:
         """
         Validate JSON data directly against the schema and return the validated Python object.
@@ -168,6 +176,8 @@ class SchemaValidator:
             allow_partial: Whether to allow partial validation; if `True` incomplete JSON will be parsed successfully
                 and errors in the last element of sequences and mappings are ignored.
                 `'trailing-strings'` means any final unfinished JSON string is included in the result.
+            by_alias: Whether to use the field's alias to match the input data to an attribute.
+            by_name: Whether to use the field's name to match the input data to an attribute.
 
         Raises:
             ValidationError: If validation fails or if the JSON data is invalid.
@@ -183,6 +193,8 @@ class SchemaValidator:
         strict: bool | None = None,
         context: Any | None = None,
         allow_partial: bool | Literal['off', 'on', 'trailing-strings'] = False,
+        by_alias: bool | None = None,
+        by_name: bool | None = None,
     ) -> Any:
         """
         Validate a string against the schema and return the validated Python object.
@@ -199,6 +211,8 @@ class SchemaValidator:
             allow_partial: Whether to allow partial validation; if `True` errors in the last element of sequences
                 and mappings are ignored.
                 `'trailing-strings'` means any final unfinished JSON string is included in the result.
+            by_alias: Whether to use the field's alias to match the input data to an attribute.
+            by_name: Whether to use the field's name to match the input data to an attribute.
 
         Raises:
             ValidationError: If validation fails or if the JSON data is invalid.
@@ -216,6 +230,8 @@ class SchemaValidator:
         strict: bool | None = None,
         from_attributes: bool | None = None,
         context: Any | None = None,
+        by_alias: bool | None = None,
+        by_name: bool | None = None,
     ) -> dict[str, Any] | tuple[dict[str, Any], dict[str, Any] | None, set[str]]:
         """
         Validate an assignment to a field on a model.
@@ -230,6 +246,8 @@ class SchemaValidator:
                 If `None`, the value of [`CoreConfig.from_attributes`][pydantic_core.core_schema.CoreConfig] is used.
             context: The context to use for validation, this is passed to functional validators as
                 [`info.context`][pydantic_core.core_schema.ValidationInfo.context].
+            by_alias: Whether to use the field's alias to match the input data to an attribute.
+            by_name: Whether to use the field's name to match the input data to an attribute.
 
         Raises:
             ValidationError: If validation fails.
@@ -283,7 +301,7 @@ class SchemaSerializer:
         mode: str | None = None,
         include: _IncEx | None = None,
         exclude: _IncEx | None = None,
-        by_alias: bool = True,
+        by_alias: bool | None = None,
         exclude_unset: bool = False,
         exclude_defaults: bool = False,
         exclude_none: bool = False,
@@ -329,7 +347,7 @@ class SchemaSerializer:
         indent: int | None = None,
         include: _IncEx | None = None,
         exclude: _IncEx | None = None,
-        by_alias: bool = True,
+        by_alias: bool | None = None,
         exclude_unset: bool = False,
         exclude_defaults: bool = False,
         exclude_none: bool = False,
@@ -374,7 +392,7 @@ def to_json(
     indent: int | None = None,
     include: _IncEx | None = None,
     exclude: _IncEx | None = None,
-    by_alias: bool = True,
+    by_alias: bool | None = None,
     exclude_none: bool = False,
     round_trip: bool = False,
     timedelta_mode: Literal['iso8601', 'float'] = 'iso8601',
@@ -450,7 +468,7 @@ def to_jsonable_python(
     *,
     include: _IncEx | None = None,
     exclude: _IncEx | None = None,
-    by_alias: bool = True,
+    by_alias: bool | None = None,
     exclude_none: bool = False,
     round_trip: bool = False,
     timedelta_mode: Literal['iso8601', 'float'] = 'iso8601',

python/pydantic_core/core_schema.py

@@ -54,8 +54,6 @@ class CoreConfig(TypedDict, total=False):
             `field_names` to construct error `loc`s. Default is `True`.
         revalidate_instances: Whether instances of models and dataclasses should re-validate. Default is 'never'.
         validate_default: Whether to validate default values during validation. Default is `False`.
-        populate_by_name: Whether an aliased field may be populated by its name as given by the model attribute,
-            as well as the alias. (Replaces 'allow_population_by_field_name' in Pydantic v1.) Default is `False`.
         str_max_length: The maximum length for string fields.
         str_min_length: The minimum length for string fields.
         str_strip_whitespace: Whether to strip whitespace from string fields.
@@ -74,6 +72,9 @@ class CoreConfig(TypedDict, total=False):
         regex_engine: The regex engine to use for regex pattern validation. Default is 'rust-regex'. See `StringSchema`.
         cache_strings: Whether to cache strings. Default is `True`, `True` or `'all'` is required to cache strings
             during general validation since validators don't know if they're in a key or a value.
+        validate_by_alias: Whether to validate by alias. Default is `True`.
+        validate_by_name: Whether to validate by attribute name. Default is `False`. Replacement for `populate_by_name`.
+        serialize_by_alias: Whether to serialize by alias. Default is `False`, expected to change to `True` in V3.
     """
 
     title: str
@@ -91,7 +92,6 @@ class CoreConfig(TypedDict, total=False):
     # whether to validate default values during validation, default False
     validate_default: bool
     # used on typed-dicts and arguments
-    populate_by_name: bool  # replaces `allow_population_by_field_name` in pydantic v1
     # fields related to string fields only
     str_max_length: int
     str_min_length: int
@@ -111,6 +111,9 @@ class CoreConfig(TypedDict, total=False):
     coerce_numbers_to_str: bool  # default: False
     regex_engine: Literal['rust-regex', 'python-re']  # default: 'rust-regex'
     cache_strings: Union[bool, Literal['all', 'keys', 'none']]  # default: 'True'
+    validate_by_alias: bool  # default: True
+    validate_by_name: bool  # default: False
+    serialize_by_alias: bool  # default: False
 
 
 IncExCall: TypeAlias = 'set[int | str] | dict[int | str, IncExCall] | None'
@@ -2888,7 +2891,6 @@ class TypedDictSchema(TypedDict, total=False):
     # all these values can be set via config, equivalent fields have `typed_dict_` prefix
     extra_behavior: ExtraBehavior
     total: bool  # default: True
-    populate_by_name: bool  # replaces `allow_population_by_field_name` in pydantic v1
     ref: str
     metadata: dict[str, Any]
     serialization: SerSchema
@@ -2904,7 +2906,6 @@ def typed_dict_schema(
     extras_schema: CoreSchema | None = None,
     extra_behavior: ExtraBehavior | None = None,
     total: bool | None = None,
-    populate_by_name: bool | None = None,
     ref: str | None = None,
     metadata: dict[str, Any] | None = None,
     serialization: SerSchema | None = None,
@@ -2938,7 +2939,6 @@ class MyTypedDict(TypedDict):
         metadata: Any other information you want to include with the schema, not used by pydantic-core
         extra_behavior: The extra behavior to use for the typed dict
         total: Whether the typed dict is total, otherwise uses `typed_dict_total` from config
-        populate_by_name: Whether the typed dict should populate by name
         serialization: Custom serialization schema
     """
     return _dict_not_none(
@@ -2950,7 +2950,6 @@ class MyTypedDict(TypedDict):
         extras_schema=extras_schema,
         extra_behavior=extra_behavior,
         total=total,
-        populate_by_name=populate_by_name,
         ref=ref,
         metadata=metadata,
         serialization=serialization,
@@ -3012,9 +3011,7 @@ class ModelFieldsSchema(TypedDict, total=False):
     computed_fields: list[ComputedField]
     strict: bool
     extras_schema: CoreSchema
-    # all these values can be set via config, equivalent fields have `typed_dict_` prefix
     extra_behavior: ExtraBehavior
-    populate_by_name: bool  # replaces `allow_population_by_field_name` in pydantic v1
     from_attributes: bool
     ref: str
     metadata: dict[str, Any]
@@ -3029,7 +3026,6 @@ def model_fields_schema(
     strict: bool | None = None,
     extras_schema: CoreSchema | None = None,
     extra_behavior: ExtraBehavior | None = None,
-    populate_by_name: bool | None = None,
     from_attributes: bool | None = None,
     ref: str | None = None,
     metadata: dict[str, Any] | None = None,
@@ -3058,7 +3054,6 @@ def model_fields_schema(
         ref: optional unique identifier of the schema, used to reference the schema in other places
         metadata: Any other information you want to include with the schema, not used by pydantic-core
         extra_behavior: The extra behavior to use for the typed dict
-        populate_by_name: Whether the typed dict should populate by name
         from_attributes: Whether the typed dict should be populated from attributes
         serialization: Custom serialization schema
     """
@@ -3070,7 +3065,6 @@ def model_fields_schema(
         strict=strict,
         extras_schema=extras_schema,
         extra_behavior=extra_behavior,
-        populate_by_name=populate_by_name,
         from_attributes=from_attributes,
         ref=ref,
         metadata=metadata,
@@ -3254,7 +3248,6 @@ class DataclassArgsSchema(TypedDict, total=False):
     dataclass_name: Required[str]
     fields: Required[list[DataclassField]]
     computed_fields: list[ComputedField]
-    populate_by_name: bool  # default: False
     collect_init_only: bool  # default: False
     ref: str
     metadata: dict[str, Any]
@@ -3267,7 +3260,6 @@ def dataclass_args_schema(
     fields: list[DataclassField],
     *,
     computed_fields: list[ComputedField] | None = None,
-    populate_by_name: bool | None = None,
     collect_init_only: bool | None = None,
     ref: str | None = None,
     metadata: dict[str, Any] | None = None,
@@ -3295,7 +3287,6 @@ def dataclass_args_schema(
         dataclass_name: The name of the dataclass being validated
         fields: The fields to use for the dataclass
         computed_fields: Computed fields to use when serializing the dataclass
-        populate_by_name: Whether to populate by name
         collect_init_only: Whether to collect init only fields into a dict to pass to `__post_init__`
         ref: optional unique identifier of the schema, used to reference the schema in other places
         metadata: Any other information you want to include with the schema, not used by pydantic-core
@@ -3307,7 +3298,6 @@ def dataclass_args_schema(
         dataclass_name=dataclass_name,
         fields=fields,
         computed_fields=computed_fields,
-        populate_by_name=populate_by_name,
         collect_init_only=collect_init_only,
         ref=ref,
         metadata=metadata,
@@ -3436,7 +3426,8 @@ def arguments_parameter(
 class ArgumentsSchema(TypedDict, total=False):
     type: Required[Literal['arguments']]
     arguments_schema: Required[list[ArgumentsParameter]]
-    populate_by_name: bool
+    validate_by_name: bool
+    validate_by_alias: bool
     var_args_schema: CoreSchema
     var_kwargs_mode: VarKwargsMode
     var_kwargs_schema: CoreSchema
@@ -3448,7 +3439,8 @@ class ArgumentsSchema(TypedDict, total=False):
 def arguments_schema(
     arguments: list[ArgumentsParameter],
     *,
-    populate_by_name: bool | None = None,
+    validate_by_name: bool | None = None,
+    validate_by_alias: bool | None = None,
     var_args_schema: CoreSchema | None = None,
     var_kwargs_mode: VarKwargsMode | None = None,
     var_kwargs_schema: CoreSchema | None = None,
@@ -3475,7 +3467,8 @@ def arguments_schema(
 
     Args:
         arguments: The arguments to use for the arguments schema
-        populate_by_name: Whether to populate by name
+        validate_by_name: Whether to populate by argument names, defaults to False.
+        validate_by_alias: Whether to populate by argument aliases, defaults to True.
         var_args_schema: The variable args schema to use for the arguments schema
         var_kwargs_mode: The validation mode to use for variadic keyword arguments. If `'uniform'`, every value of the
             keyword arguments will be validated against the `var_kwargs_schema` schema. If `'unpacked-typed-dict'`,
@@ -3488,7 +3481,8 @@ def arguments_schema(
     return _dict_not_none(
         type='arguments',
         arguments_schema=arguments,
-        populate_by_name=populate_by_name,
+        validate_by_name=validate_by_name,
+        validate_by_alias=validate_by_alias,
         var_args_schema=var_args_schema,
         var_kwargs_mode=var_kwargs_mode,
         var_kwargs_schema=var_kwargs_schema,

src/errors/validation_exception.rs

@@ -344,7 +344,7 @@ impl ValidationError {
         let extra = state.extra(
             py,
             &SerMode::Json,
-            true,
+            None,
             false,
             false,
             true,

src/lookup_key.rs

@@ -577,3 +577,47 @@ fn py_get_attrs<'py>(obj: &Bound<'py, PyAny>, attr_name: &Py<PyString>) -> PyRes
         }
     }
 }
+
+#[derive(Debug)]
+#[allow(clippy::struct_field_names)]
+pub struct LookupKeyCollection {
+    by_name: LookupKey,
+    by_alias: Option<LookupKey>,
+    by_alias_then_name: Option<LookupKey>,
+}
+
+impl LookupKeyCollection {
+    pub fn new(py: Python, validation_alias: Option<Bound<'_, PyAny>>, field_name: &str) -> PyResult<Self> {
+        let by_name = LookupKey::from_string(py, field_name);
+
+        if let Some(va) = validation_alias {
+            let by_alias = Some(LookupKey::from_py(py, &va, None)?);
+            let by_alias_then_name = Some(LookupKey::from_py(py, &va, Some(field_name))?);
+            Ok(Self {
+                by_name,
+                by_alias,
+                by_alias_then_name,
+            })
+        } else {
+            Ok(Self {
+                by_name,
+                by_alias: None,
+                by_alias_then_name: None,
+            })
+        }
+    }
+
+    pub fn select(&self, validate_by_alias: bool, validate_by_name: bool) -> PyResult<&LookupKey> {
+        let lookup_key_selection = match (validate_by_alias, validate_by_name) {
+            (true, true) => self.by_alias_then_name.as_ref().unwrap_or(&self.by_name),
+            (true, false) => self.by_alias.as_ref().unwrap_or(&self.by_name),
+            (false, true) => &self.by_name,
+            (false, false) => {
+                // Note: we shouldn't hit this branch much, as this is enforced in `pydantic` with a `PydanticUserError`
+                // at config creation time / validation function call time.
+                return py_schema_err!("`validate_by_name` and `validate_by_alias` cannot both be set to `False`.");
+            }
+        };
+        Ok(lookup_key_selection)
+    }
+}

src/serializers/computed_fields.rs

@@ -98,7 +98,7 @@ impl ComputedFields {
                     exclude: next_exclude.as_ref(),
                     extra: &field_extra,
                 };
-                let key = match extra.by_alias {
+                let key = match extra.serialize_by_alias_or(computed_field.serialize_by_alias) {
                     true => computed_field.alias.as_str(),
                     false => computed_field.property_name.as_str(),
                 };
@@ -116,6 +116,7 @@ struct ComputedField {
     serializer: CombinedSerializer,
     alias: String,
     alias_py: Py<PyString>,
+    serialize_by_alias: bool,
 }
 
 impl ComputedField {
@@ -133,12 +134,14 @@ impl ComputedField {
         let alias_py = schema
             .get_as(intern!(py, "alias"))?
             .unwrap_or_else(|| property_name.clone());
+        let serialize_by_alias = config.get_as(intern!(py, "serialize_by_alias"))?.unwrap_or(false);
         Ok(Self {
             property_name: property_name.extract()?,
             property_name_py: property_name.into(),
             serializer,
             alias: alias_py.extract()?,
             alias_py: alias_py.into(),
+            serialize_by_alias,
         })
     }
 
@@ -163,7 +166,7 @@ impl ComputedField {
             if extra.exclude_none && value.is_none(py) {
                 return Ok(());
             }
-            let key = match extra.by_alias {
+            let key = match extra.serialize_by_alias_or(self.serialize_by_alias) {
                 true => self.alias_py.bind(py),
                 false => property_name_py,
             };