Try to evaluate forward refs after model created (#2588)

* Try to evaluate forward refs after model created

* Upadate docs and remove code duplication

* Update changes/2588-uriyyo.md

Co-authored-by: Eric Jolibois <em.jolibois@gmail.com>

* Update docs/usage/postponed_annotations.md

Co-authored-by: Eric Jolibois <em.jolibois@gmail.com>

* Remove unused import

Co-authored-by: Eric Jolibois <em.jolibois@gmail.com>

changes/2588-uriyyo.md

@@ -0,0 +1 @@
+Try to evaluate forward refs automatically at model creation.

docs/examples/postponed_annotations_self_referencing_annotations.py

@@ -8,7 +8,5 @@ class Foo(BaseModel):
     sibling: Foo = None
 
 
-Foo.update_forward_refs()
-
 print(Foo())
 print(Foo(sibling={'a': '321'}))

docs/examples/postponed_annotations_self_referencing_string.py

@@ -7,7 +7,5 @@ class Foo(BaseModel):
     sibling: 'Foo' = None
 
 
-Foo.update_forward_refs()
-
 print(Foo())
 print(Foo(sibling={'a': '321'}))

docs/usage/postponed_annotations.md

@@ -45,9 +45,8 @@ Resolving this is beyond the call for *pydantic*: either remove the future impor
 
 ## Self-referencing Models
 
-Data structures with self-referencing models are also supported, provided the function
-`update_forward_refs()` is called once the model is created (you will be reminded
-with a friendly error message if you forget).
+Data structures with self-referencing models are also supported. Self-referencing fields will be automatically
+resolved after model creation.
 
 Within the model, you can refer to the not-yet-constructed model using a string:
 

pydantic/main.py

@@ -1,4 +1,3 @@
-import sys
 import warnings
 from abc import ABCMeta
 from copy import deepcopy
@@ -42,7 +41,7 @@ from .typing import (
     is_namedtuple,
     is_union_origin,
     resolve_annotations,
-    update_field_forward_refs,
+    update_model_forward_refs,
 )
 from .utils import (
     ROOT_KEY,
@@ -289,6 +288,8 @@ class ModelMetaclass(ABCMeta):
         cls = super().__new__(mcs, name, bases, new_namespace, **kwargs)
         # set __signature__ attr only for model class, but not for its instances
         cls.__signature__ = ClassAttribute('__signature__', generate_model_signature(cls.__init__, fields, config))
+        cls.__try_update_forward_refs__()
+
         return cls
 
 
@@ -746,15 +747,20 @@ class BaseModel(Representation, metaclass=ModelMetaclass):
         else:
             return v
 
+    @classmethod
+    def __try_update_forward_refs__(cls) -> None:
+        """
+        Same as update_forward_refs but will not raise exception
+        when forward references are not defined.
+        """
+        update_model_forward_refs(cls, cls.__fields__.values(), {}, (NameError,))
+
     @classmethod
     def update_forward_refs(cls, **localns: Any) -> None:
         """
         Try to update ForwardRefs on fields based on this Model, globalns and localns.
         """
-        globalns = sys.modules[cls.__module__].__dict__.copy()
-        globalns.setdefault(cls.__name__, cls)
-        for f in cls.__fields__.values():
-            update_field_forward_refs(f, globalns=globalns, localns=localns)
+        update_model_forward_refs(cls, cls.__fields__.values(), localns)
 
     def __iter__(self) -> 'TupleGenerator':
         """

pydantic/typing.py

@@ -7,6 +7,7 @@ from typing import (  # type: ignore
     ClassVar,
     Dict,
     Generator,
+    Iterable,
     List,
     Mapping,
     NewType,
@@ -251,6 +252,7 @@ __all__ = (
     'new_type_supertype',
     'is_classvar',
     'update_field_forward_refs',
+    'update_model_forward_refs',
     'TupleGenerator',
     'DictStrAny',
     'DictAny',
@@ -441,6 +443,29 @@ def update_field_forward_refs(field: 'ModelField', globalns: Any, localns: Any)
             update_field_forward_refs(sub_f, globalns=globalns, localns=localns)
 
 
+def update_model_forward_refs(
+    model: Type[Any],
+    fields: Iterable['ModelField'],
+    localns: 'DictStrAny',
+    exc_to_suppress: Tuple[Type[BaseException], ...] = (),
+) -> None:
+    """
+    Try to update model fields ForwardRefs based on model and localns.
+    """
+    if model.__module__ in sys.modules:
+        globalns = sys.modules[model.__module__].__dict__.copy()
+    else:
+        globalns = {}
+
+    globalns.setdefault(model.__name__, model)
+
+    for f in fields:
+        try:
+            update_field_forward_refs(f, globalns=globalns, localns=localns)
+        except exc_to_suppress:
+            pass
+
+
 def get_class(type_: Type[Any]) -> Union[None, bool, Type[Any]]:
     """
     Tries to get the class of a Type[T] annotation. Returns True if Type is used

tests/test_forward_ref.py

@@ -41,6 +41,57 @@ class Model(BaseModel):
     assert module.Model().dict() == {'a': None}
 
 
+@skip_pre_37
+def test_postponed_annotations_auto_update_forward_refs(create_module):
+    module = create_module(
+        # language=Python
+        """
+from __future__ import annotations
+from pydantic import BaseModel
+
+class Model(BaseModel):
+    a: Model
+"""
+    )
+
+    assert module.Model.__fields__['a'].type_ is module.Model
+
+
+def test_forward_ref_auto_update_no_model(create_module):
+    module = create_module(
+        # language=Python
+        """
+from pydantic import BaseModel
+
+class Foo(BaseModel):
+    a: 'Bar'
+
+class Bar(BaseModel):
+    b: 'Foo'
+"""
+    )
+
+    from pydantic.typing import ForwardRef
+
+    assert module.Foo.__fields__['a'].type_ == ForwardRef('Bar')
+    assert module.Bar.__fields__['b'].type_ is module.Foo
+
+
+def test_forward_ref_one_of_fields_not_defined(create_module):
+    @create_module
+    def module():
+        from pydantic import BaseModel
+
+        class Foo(BaseModel):
+            foo: 'Foo'
+            bar: 'Bar'  # noqa: F821
+
+    from pydantic.typing import ForwardRef
+
+    assert module.Foo.__fields__['bar'].type_ == ForwardRef('Bar')
+    assert module.Foo.__fields__['foo'].type_ is module.Foo
+
+
 def test_basic_forward_ref(create_module):
     @create_module
     def module():
@@ -509,14 +560,6 @@ def test_nested_forward_ref():
     class NestedTuple(BaseModel):
         x: Tuple[int, Optional['NestedTuple']]  # noqa: F821
 
-    with pytest.raises(ConfigError) as exc_info:
-        NestedTuple.parse_obj({'x': ('1', {'x': ('2', {'x': ('3', None)})})})
-    assert str(exc_info.value) == (
-        'field "x_1" not yet prepared so type is still a ForwardRef, '
-        'you might need to call NestedTuple.update_forward_refs().'
-    )
-
-    NestedTuple.update_forward_refs()
     obj = NestedTuple.parse_obj({'x': ('1', {'x': ('2', {'x': ('3', None)})})})
     assert obj.dict() == {'x': (1, {'x': (2, {'x': (3, None)})})}