check ModelField().validate_always when inheriting (pydantic#1545)

fix pydantic#1155

* fix issure pydantic#1155

* add changes.1545-dcHHH.md

* improve change description

Co-authored-by: dchhh <hudacong@geetest.com>
Co-authored-by: Samuel Colvin <samcolvin@gmail.com>

changes/1545-dcHHH.md

@@ -0,0 +1 @@
+Move the assignment of `field.validate_always` in `fields.py` so the `always` parameter of validators work on inheritance.

pydantic/fields.py

@@ -365,10 +365,6 @@ def prepare(self) -> None:
             # user will need to call model.update_forward_refs()
             return
 
-        self.validate_always = getattr(self.type_, 'validate_always', False) or any(
-            v.always for v in self.class_validators.values()
-        )
-
         if self.required is False and default_value is None:
             self.allow_none = True
 
@@ -511,6 +507,10 @@ def populate_validators(self) -> None:
         and class validators. This method should be idempotent, e.g. it should be safe to call multiple times
         without mis-configuring the field.
         """
+        self.validate_always = getattr(self.type_, 'validate_always', False) or any(
+            v.always for v in self.class_validators.values()
+        )
+
         class_validators_ = self.class_validators.values()
         if not self.sub_fields or self.shape == SHAPE_GENERIC:
             get_validators = getattr(self.type_, '__get_validators__', None)

tests/test_validators.py

@@ -287,6 +287,25 @@ def check_a(cls, v):
     assert check_calls == 2
 
 
+def test_validate_always_on_inheritance():
+    check_calls = 0
+
+    class ParentModel(BaseModel):
+        a: str = None
+
+    class Model(ParentModel):
+        @validator('a', pre=True, always=True)
+        def check_a(cls, v):
+            nonlocal check_calls
+            check_calls += 1
+            return v or 'xxx'
+
+    assert Model().a == 'xxx'
+    assert check_calls == 1
+    assert Model(a='y').a == 'y'
+    assert check_calls == 2
+
+
 def test_validate_not_always():
     check_calls = 0