Fix issue with double model parsing

fastapi/dependencies/utils.py

@@ -467,7 +467,8 @@ async def solve_dependencies(
         media_type=None,  # type: ignore # in Starlette
         background=None,  # type: ignore # in Starlette
     )
-    dependency_cache = dependency_cache or {}
+    if dependency_cache is None:
+        dependency_cache = {}
     sub_dependant: Dependant
     for sub_dependant in dependant.dependencies:
         sub_dependant.call = cast(Callable[..., Any], sub_dependant.call)
@@ -493,7 +494,21 @@ async def solve_dependencies(
             )
             use_sub_dependant.security_scopes = sub_dependant.security_scopes
 
-        solved_result = await solve_dependencies(
+        if sub_dependant.use_cache and sub_dependant.cache_key in dependency_cache:
+            solved = dependency_cache[sub_dependant.cache_key]
+
+            if sub_dependant.name is not None:
+                values[sub_dependant.name] = solved
+
+            continue
+
+        (
+            sub_values,
+            sub_errors,
+            background_tasks,
+            _,  # the subdependency returns the same response we have
+            sub_dependency_cache,
+        ) = await solve_dependencies(
             request=request,
             dependant=use_sub_dependant,
             body=body,
@@ -502,19 +517,10 @@ async def solve_dependencies(
             dependency_overrides_provider=dependency_overrides_provider,
             dependency_cache=dependency_cache,
         )
-        (
-            sub_values,
-            sub_errors,
-            background_tasks,
-            _,  # the subdependency returns the same response we have
-            sub_dependency_cache,
-        ) = solved_result
         dependency_cache.update(sub_dependency_cache)
         if sub_errors:
             errors.extend(sub_errors)
             continue
-        if sub_dependant.use_cache and sub_dependant.cache_key in dependency_cache:
-            solved = dependency_cache[sub_dependant.cache_key]
         elif is_gen_callable(call) or is_async_gen_callable(call):
             stack = request.scope.get("fastapi_astack")
             assert isinstance(stack, AsyncExitStack)

tests/test_dependency_cache.py

@@ -1,9 +1,21 @@
 from fastapi import Depends, FastAPI
 from fastapi.testclient import TestClient
+from pydantic import BaseModel, root_validator
 
 app = FastAPI()
 
-counter_holder = {"counter": 0}
+counter_holder = {"counter": 0, "parsing_counter": 0}
+
+
+class Model(BaseModel):
+    @root_validator
+    def __validate__(cls, _):
+        counter_holder["parsing_counter"] += 1
+        return {}
+
+
+async def model_dep(model: Model) -> Model:
+    return model
 
 
 async def dep_counter():
@@ -35,6 +47,15 @@ async def get_sub_counter_no_cache(
     return {"counter": count, "subcounter": subcount}
 
 
+@app.post("/sub-model-parsing/")
+async def get_double_model_parsing(
+    a: Model = Depends(model_dep),
+    b: Model = Depends(model_dep),
+):
+    assert a is b
+    return {"parsing_counter": counter_holder["parsing_counter"]}
+
+
 client = TestClient(app)
 
 
@@ -66,3 +87,10 @@ def test_sub_counter_no_cache():
     response = client.get("/sub-counter-no-cache/")
     assert response.status_code == 200, response.text
     assert response.json() == {"counter": 4, "subcounter": 3}
+
+
+def test_sub_model_parsing_no_repeatable_parsing():
+    counter_holder["parsing_counter"] = 0
+    response = client.post("/sub-model-parsing/", json={})
+    assert response.status_code == 200, response.text
+    assert response.json() == {"parsing_counter": 1}