✏️ Add documentation on using context managers as dependencies

docs/en/docs/tutorial/dependencies/dependencies-with-yield.md

@@ -17,6 +17,8 @@ To do this, use `yield` instead of `return`, and write the extra steps after.
 
     In fact, FastAPI uses those two decorators internally.
 
+    And if you have a context manager already, you can use it as a dependency, too.
+
 ## A database dependency with `yield`
 
 For example, you could use this to create a database session and close it after finishing.
@@ -222,32 +224,38 @@ When the `with` block finishes, it makes sure to close the file, even if there w
 
 When you create a dependency with `yield`, **FastAPI** will internally convert it to a context manager, and combine it with some other related tools.
 
-### Using context managers in dependencies with `yield`
+## Context Managers as dependencies
+
+You don’t have to create a Context Manager to use FastAPI dependencies.
+
+But sometimes you might want to use a dependency both inside and outside FastAPI. For example, you might want to connect to a database in a DB migration script. You can create a Context Manager manually then:
+
+```Python
+{!../../../docs_src/dependencies/tutorial010_ctx.py!}
+```
+
+This way you can use it with `Depends()` in your app, and as a regular Context Manager everywhere else:
+
+```Python
+{!../../../docs_src/dependencies/tutorial010_ctx_usage.py!}
+```
+
+
+### Defining Context Managers as classes
 
 !!! warning
     This is, more or less, an "advanced" idea.
 
     If you are just starting with **FastAPI** you might want to skip it for now.
 
-In Python, you can create Context Managers by <a href="https://docs.python.org/3/reference/datamodel.html#context-managers" class="external-link" target="_blank">creating a class with two methods: `__enter__()` and `__exit__()`</a>.
+You can also create Context Managers by <a href="https://docs.python.org/3/reference/datamodel.html#context-managers" class="external-link" target="_blank">creating a class with two methods: `__enter__()` and `__exit__()`</a>.
 
-You can also use them inside of **FastAPI** dependencies with `yield` by using
-`with` or `async with` statements inside of the dependency function:
+Like the Context Managers created with `contextlib`, you can use them inside of **FastAPI** dependencies directly:
 
 ```Python hl_lines="1-9  13"
 {!../../../docs_src/dependencies/tutorial010.py!}
 ```
 
-!!! tip
-    Another way to create a context manager is with:
-
-    * <a href="https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager" class="external-link" target="_blank">`@contextlib.contextmanager`</a> or
-    * <a href="https://docs.python.org/3/library/contextlib.html#contextlib.asynccontextmanager" class="external-link" target="_blank">`@contextlib.asynccontextmanager`</a>
-
-    using them to decorate a function with a single `yield`.
-
-    That's what **FastAPI** uses internally for dependencies with `yield`.
 
-    But you don't have to use the decorators for FastAPI dependencies (and you shouldn't).
-
-    FastAPI will do it for you internally.
+!!! note "Technical Details"
+    Internally, FastAPI calls the dependency function and then checks if the result has either an `__enter__()` or an `__aenter__()` method. If that’s the case, it will treat it as a context manager.

docs_src/dependencies/tutorial010.py

@@ -9,6 +9,6 @@ class MySuperContextManager:
         self.db.close()
 
 
-async def get_db():
-    with MySuperContextManager() as db:
-        yield db
+@app.get("/")
+async def get_root(db: Annotated[DBSession, Depends(MySuperContextManager)]):
+    ...

docs_src/dependencies/tutorial010_ctx.py

@@ -0,0 +1,9 @@
+from contextlib import asynccontextmanager
+
+@asynccontextmanager
+async def get_db():
+    db = DBSession()
+    try:
+        yield db
+    finally:
+        db.close()

docs_src/dependencies/tutorial010_ctx_usage.py

@@ -0,0 +1,3 @@
+async def migrate():
+    with get_db() as db:
+        ...