From a2fc01a59bf1d3500f651ba28ef809671f323aab Mon Sep 17 00:00:00 2001
From: PrettyWood <em.jolibois@gmail.com>
Date: Thu, 8 Oct 2020 21:26:30 +0200
Subject: [PATCH] fix: forward ref with nested models and optional fields
 (#1752)

* fix: forward ref with nested models and optional fields

PR #1712 introduced a regression for forward refs in `ModelField.prepare`
as it would not return early for forward refs anymore.
Optional fields would hence have `required` set to `True`.

closes #1736

* test: skip python 3.6 as __future__.annotations is not defined
---
 changes/1736-PrettyWood.md |  1 +
 pydantic/fields.py         | 10 +++++-----
 tests/test_forward_ref.py  | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+), 5 deletions(-)
 create mode 100644 changes/1736-PrettyWood.md

diff --git a/changes/1736-PrettyWood.md b/changes/1736-PrettyWood.md
new file mode 100644
index 0000000..64a22ab
--- /dev/null
+++ b/changes/1736-PrettyWood.md
@@ -0,0 +1 @@
+Fix behaviour with forward refs and optional fields in nested models
\ No newline at end of file
diff --git a/pydantic/fields.py b/pydantic/fields.py
index 6ab039c..c162616 100644
--- a/pydantic/fields.py
+++ b/pydantic/fields.py
@@ -334,6 +334,11 @@ class ModelField(Representation):
         """
 
         self._set_default_and_type()
+        if self.type_.__class__ == ForwardRef:
+            # self.type_ is currently a ForwardRef and there's nothing we can do now,
+            # user will need to call model.update_forward_refs()
+            return
+
         self._type_analysis()
         if self.required is Undefined:
             self.required = True
@@ -366,11 +371,6 @@ class ModelField(Representation):
         if self.type_ is None:
             raise errors_.ConfigError(f'unable to infer type for attribute "{self.name}"')
 
-        if self.type_.__class__ == ForwardRef:
-            # self.type_ is currently a ForwardRef and there's nothing we can do now,
-            # user will need to call model.update_forward_refs()
-            return
-
         if self.required is False and default_value is None:
             self.allow_none = True
 
diff --git a/tests/test_forward_ref.py b/tests/test_forward_ref.py
index d640dd7..420079d 100644
--- a/tests/test_forward_ref.py
+++ b/tests/test_forward_ref.py
@@ -439,3 +439,36 @@ else:
     raise AssertionError('error not raised')
     """
     )
+
+
+@skip_pre_37
+def test_forward_ref_optional(create_module):
+    module = create_module(
+        """
+from __future__ import annotations
+from pydantic import BaseModel, Field
+from typing import List, Optional
+
+
+class Spec(BaseModel):
+    spec_fields: List[str] = Field(..., alias="fields")
+    filter: Optional[str]
+    sort: Optional[str]
+
+
+class PSpec(Spec):
+    g: Optional[GSpec]
+
+
+class GSpec(Spec):
+    p: Optional[PSpec]
+
+PSpec.update_forward_refs()
+
+class Filter(BaseModel):
+    g: Optional[GSpec]
+    p: Optional[PSpec]
+    """
+    )
+    Filter = module.Filter
+    assert isinstance(Filter(p={'sort': 'some_field:asc', 'fields': []}), Filter)