Sebastián Ramírez <******@****.***> 1688149516 +0200

@app.post("/no-duplicates")
async def no_duplicates(item: Item, item2: Item = Depends(dependency)):
    return [item, item2]


@app.post("/with-duplicates-sub")
async def no_duplicates_sub(
    item: Item, sub_items: List[Item] = Depends(sub_duplicate_dependency)
):
    return [item, sub_items]


def test_no_duplicates_invalid():
    response = client.post("/no-duplicates", json={"item": {"data": "myitem"}})

## Duplicate headers

It is possible to receive duplicate headers. That means, the same header with multiple values.

You can define those cases using a list in the type declaration.

You will receive all the values from the duplicate header as a Python `list`.

    if route.description:
        operation["description"] = route.description
    operation_id = route.operation_id or route.unique_id
    if operation_id in operation_ids:
        message = (
            f"Duplicate Operation ID {operation_id} for function "
            + f"{route.endpoint.__name__}"
        )
        file_name = getattr(route.endpoint, "__globals__", {}).get("__file__")
        if file_name:

        warnings.simplefilter("always")
        client.get("/openapi.json")
        assert len(w) >= 2
        duplicate_warnings = [
            warning for warning in w if issubclass(warning.category, UserWarning)
        ]
        assert len(duplicate_warnings) > 0

    ```Python hl_lines="1  14"
    {!> ../../../docs_src/body_nested_models/tutorial003.py!}
    ```

With this, even if you receive a request with duplicate data, it will be converted to a set of unique items.

And whenever you output that data, even if the source had duplicates, it will be output as a set of unique items.

And it will be annotated / documented accordingly too.

## Nested Models

* `frozenset`:
    * Wird in Requests und Responses wie ein `set` behandelt:
        * Bei Requests wird eine Liste gelesen, Duplikate entfernt und in ein `set` umgewandelt.
        * Bei Responses wird das `set` in eine `list`e umgewandelt.
        * Das generierte Schema zeigt an, dass die `set`-Werte eindeutig sind (unter Verwendung von JSON Schemas `uniqueItems`).

É possível receber cabeçalhos duplicados. Isso significa, o mesmo cabeçalho com vários valores.

Você pode definir esses casos usando uma lista na declaração de tipo.

Você receberá todos os valores do cabeçalho duplicado como uma `list` Python.

Por exemplo, para declarar um cabeçalho de `X-Token` que pode aparecer mais de uma vez, você pode escrever:

=== "Python 3.10+"

    ```Python hl_lines="7"

And you would also use Alembic for "migrations" (that's its main job).

A "migration" is the set of steps needed whenever you change the structure of your SQLAlchemy models, add a new attribute, etc. to replicate those changes in the database, add a new column, a new table, etc.

single process running those previous steps *even* if afterwards, you start **multiple processes** (multiple workers) for the application itself. If those steps were run by **multiple processes**, they would **duplicate** the work by running it on **parallel**, and if the steps were something delicate like a database migration, they could cause conflicts with each other.

Of course, there are some cases where there's no problem in running the previous steps multiple times, in that case, it's...