Change alias precedence to prefer child models (#904)

* Change alias precedence to prefer child models

* add docs about alias precedence

* correct change

changes/904-samuelcolvin.md

@@ -0,0 +1,2 @@
+**Breaking Change:** Change the precedence of aliases so child model aliases override parent aliases, 
+including using `alias_generator`

docs/examples/alias_generator_config.py

@@ -5,12 +5,11 @@ def to_camel(string: str) -> str:
 
 class Voice(BaseModel):
     name: str
-    gender: str
     language_code: str
 
     class Config:
         alias_generator = to_camel
 
-voice = Voice(Name='Filiz', Gender='Female', LanguageCode='tr-TR')
+voice = Voice(Name='Filiz', LanguageCode='tr-TR')
 print(voice.language_code)
 print(voice.dict(by_alias=True))

docs/examples/alias_precedence.py

@@ -0,0 +1,21 @@
+from pydantic import BaseModel
+
+class Voice(BaseModel):
+    name: str
+    language_code: str
+
+    class Config:
+        @classmethod
+        def alias_generator(cls, string: str) -> str:
+            # this is the same as `alias_generator = to_camel` above
+            return ''.join(word.capitalize() for word in string.split('_'))
+
+class Character(Voice):
+    mood: str
+
+    class Config:
+        fields = {'mood': 'Mood', 'language_code': 'lang'}
+
+c = Character(Mood='happy', Name='Filiz', lang='tr-TR')
+print(c)
+print(c.dict(by_alias=True))

docs/usage/model_config.md

@@ -98,3 +98,16 @@ you can automatically generate aliases using `alias_generator`:
 {!.tmp_examples/alias_generator_config.py!}
 ```
 _(This script is complete, it should run "as is")_
+
+
+## Alias Precedence
+
+Aliases defined on the `Config` class of child models will take priority over any aliases defined on `Config` of a
+parent model:
+
+```py
+{!.tmp_examples/alias_precedence.py!}
+```
+_(This script is complete, it should run "as is")_
+
+This includes when a child model uses `alias_generator` where the aliases of all parent model fields will be updated.

mkdocs.yml

@@ -29,7 +29,7 @@ nav:
   - usage/models.md
   - 'Field Types': usage/types.md
   - usage/validators.md
-  - usage/model_config.md
+  - 'Model Config': usage/model_config.md
   - usage/schema.md
   - usage/exporting_models.md
   - usage/dataclasses.md

pydantic/fields.py

@@ -263,10 +263,10 @@ def infer(
 
     def set_config(self, config: Type['BaseConfig']) -> None:
         self.model_config = config
-        schema_from_config = config.get_field_info(self.name)
-        if schema_from_config:
+        info_from_config = config.get_field_info(self.name)
+        if info_from_config:
             self.field_info = cast(FieldInfo, self.field_info)
-            self.field_info.alias = self.field_info.alias or schema_from_config.get('alias') or self.name
+            self.field_info.alias = info_from_config.get('alias') or self.field_info.alias or self.name
             self.alias = cast(str, self.field_info.alias)
 
     @property

tests/test_edge_cases.py

@@ -1079,3 +1079,43 @@ class Model(BaseModel):
 
     assert Model().__fields__.keys() == {'v'}
     assert Model.__fields__.keys() == {'v'}
+
+
+def test_alias_child_precedence():
+    class Parent(BaseModel):
+        x: int
+
+        class Config:
+            fields = {'x': 'x1'}
+
+    class Child(Parent):
+        y: int
+
+        class Config:
+            fields = {'y': 'y2', 'x': 'x2'}
+
+    assert Child.__fields__['y'].alias == 'y2'
+    assert Child.__fields__['x'].alias == 'x2'
+
+
+def test_alias_generator_parent():
+    class Parent(BaseModel):
+        x: int
+
+        class Config:
+            allow_population_by_field_name = True
+
+            @classmethod
+            def alias_generator(cls, f_name):
+                return f_name + '1'
+
+    class Child(Parent):
+        y: int
+
+        class Config:
+            @classmethod
+            def alias_generator(cls, f_name):
+                return f_name + '2'
+
+    assert Child.__fields__['y'].alias == 'y2'
+    assert Child.__fields__['x'].alias == 'x2'