✨ Add dependencies with yield (used as context managers) (#595)

* ➕ Add development/testing dependencies for Python 3.6

* ✨ Add concurrency submodule with contextmanager_in_threadpool

* ✨ Add AsyncExitStack to ASGI scope in FastAPI app call

* ✨ Use async stack for contextmanager-able dependencies

including running in threadpool sync dependencies

* ✅ Add tests for contextmanager dependencies

including internal raise checks when exceptions should be handled and when not

* ✅ Add test for fake asynccontextmanager raiser

* 🐛 Fix mypy errors and coverage

* 🔇 Remove development logs and prints

* ✅ Add tests for sub-contextmanagers, background tasks, and sync functions

* 🐛 Fix mypy errors for Python 3.7

* 💬 Fix error texts for clarity

* 📝 Add docs for dependencies with yield

* ✨ Update SQL with SQLAlchemy tutorial to use dependencies with yield

and add an alternative with a middleware (from the old tutorial)

* ✅ Update SQL tests to remove DB file during the same tests

* ✅ Add tests for example with middleware

as a copy from the tests with dependencies with yield, removing the DB in the tests

* ✏️ Fix typos with suggestions from code review

Co-Authored-By: dmontagu <35119617+dmontagu@users.noreply.github.com>

docs/src/dependencies/tutorial007.py

@@ -1,21 +1,6 @@
-from fastapi import Depends, FastAPI
-
-app = FastAPI()
-
-
-class FixedContentQueryChecker:
-    def __init__(self, fixed_content: str):
-        self.fixed_content = fixed_content
-
-    def __call__(self, q: str = ""):
-        if q:
-            return self.fixed_content in q
-        return False
-
-
-checker = FixedContentQueryChecker("bar")
-
-
-@app.get("/query-checker/")
-async def read_query_check(fixed_content_included: bool = Depends(checker)):
-    return {"fixed_content_in_query": fixed_content_included}
+async def get_db():
+    db = DBSession()
+    try:
+        yield db
+    finally:
+        db.close()

docs/src/dependencies/tutorial008.py

@@ -0,0 +1,25 @@
+from fastapi import Depends
+
+
+async def dependency_a():
+    dep_a = generate_dep_a()
+    try:
+        yield dep_a
+    finally:
+        dep_a.close()
+
+
+async def dependency_b(dep_a=Depends(dependency_a)):
+    dep_b = generate_dep_b()
+    try:
+        yield dep_b
+    finally:
+        dep_b.close(dep_a)
+
+
+async def dependency_c(dep_b=Depends(dependency_b)):
+    dep_c = generate_dep_c()
+    try:
+        yield dep_c
+    finally:
+        dep_c.close(dep_b)

docs/src/dependencies/tutorial009.py

@@ -0,0 +1,25 @@
+from fastapi import Depends
+
+
+async def dependency_a():
+    dep_a = generate_dep_a()
+    try:
+        yield dep_a
+    finally:
+        dep_a.close()
+
+
+async def dependency_b(dep_a=Depends(dependency_a)):
+    dep_b = generate_dep_b()
+    try:
+        yield dep_b
+    finally:
+        dep_b.close(dep_a)
+
+
+async def dependency_c(dep_b=Depends(dependency_b)):
+    dep_c = generate_dep_c()
+    try:
+        yield dep_c
+    finally:
+        dep_c.close(dep_b)

docs/src/dependencies/tutorial010.py

@@ -0,0 +1,14 @@
+class MySuperContextManager:
+    def __init__(self):
+        self.db = DBSession()
+
+    def __enter__(self):
+        return self.db
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.db.close()
+
+
+async def get_db():
+    with MySuperContextManager() as db:
+        yield db

docs/src/dependencies/tutorial011.py

@@ -0,0 +1,21 @@
+from fastapi import Depends, FastAPI
+
+app = FastAPI()
+
+
+class FixedContentQueryChecker:
+    def __init__(self, fixed_content: str):
+        self.fixed_content = fixed_content
+
+    def __call__(self, q: str = ""):
+        if q:
+            return self.fixed_content in q
+        return False
+
+
+checker = FixedContentQueryChecker("bar")
+
+
+@app.get("/query-checker/")
+async def read_query_check(fixed_content_included: bool = Depends(checker)):
+    return {"fixed_content_in_query": fixed_content_included}

docs/src/sql_databases/sql_app/alt_main.py

@@ -0,0 +1,64 @@
+from typing import List
+
+from fastapi import Depends, FastAPI, HTTPException
+from sqlalchemy.orm import Session
+from starlette.requests import Request
+from starlette.responses import Response
+
+from . import crud, models, schemas
+from .database import SessionLocal, engine
+
+models.Base.metadata.create_all(bind=engine)
+
+app = FastAPI()
+
+
+@app.middleware("http")
+async def db_session_middleware(request: Request, call_next):
+    response = Response("Internal server error", status_code=500)
+    try:
+        request.state.db = SessionLocal()
+        response = await call_next(request)
+    finally:
+        request.state.db.close()
+    return response
+
+
+# Dependency
+def get_db(request: Request):
+    return request.state.db
+
+
+@app.post("/users/", response_model=schemas.User)
+def create_user(user: schemas.UserCreate, db: Session = Depends(get_db)):
+    db_user = crud.get_user_by_email(db, email=user.email)
+    if db_user:
+        raise HTTPException(status_code=400, detail="Email already registered")
+    return crud.create_user(db=db, user=user)
+
+
+@app.get("/users/", response_model=List[schemas.User])
+def read_users(skip: int = 0, limit: int = 100, db: Session = Depends(get_db)):
+    users = crud.get_users(db, skip=skip, limit=limit)
+    return users
+
+
+@app.get("/users/{user_id}", response_model=schemas.User)
+def read_user(user_id: int, db: Session = Depends(get_db)):
+    db_user = crud.get_user(db, user_id=user_id)
+    if db_user is None:
+        raise HTTPException(status_code=404, detail="User not found")
+    return db_user
+
+
+@app.post("/users/{user_id}/items/", response_model=schemas.Item)
+def create_item_for_user(
+    user_id: int, item: schemas.ItemCreate, db: Session = Depends(get_db)
+):
+    return crud.create_user_item(db=db, item=item, user_id=user_id)
+
+
+@app.get("/items/", response_model=List[schemas.Item])
+def read_items(skip: int = 0, limit: int = 100, db: Session = Depends(get_db)):
+    items = crud.get_items(db, skip=skip, limit=limit)
+    return items

docs/src/sql_databases/sql_app/main.py

@@ -2,8 +2,6 @@ from typing import List
 
 from fastapi import Depends, FastAPI, HTTPException
 from sqlalchemy.orm import Session
-from starlette.requests import Request
-from starlette.responses import Response
 
 from . import crud, models, schemas
 from .database import SessionLocal, engine
@@ -13,20 +11,13 @@ models.Base.metadata.create_all(bind=engine)
 app = FastAPI()
 
 
-@app.middleware("http")
-async def db_session_middleware(request: Request, call_next):
-    response = Response("Internal server error", status_code=500)
-    try:
-        request.state.db = SessionLocal()
-        response = await call_next(request)
-    finally:
-        request.state.db.close()
-    return response
-
-
 # Dependency
-def get_db(request: Request):
-    return request.state.db
+def get_db():
+    try:
+        db = SessionLocal()
+        yield db
+    finally:
+        db.close()
 
 
 @app.post("/users/", response_model=schemas.User)