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`.

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...

        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

    with warnings.catch_warnings(record=True) as w:
        warnings.simplefilter("always")
        response = client.get("/openapi.json")
        assert issubclass(w[-1].category, UserWarning)
        assert "Duplicate Operation ID" in str(w[-1].message)
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/override1": {

    ```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

    ```

Jetzt, selbst wenn Sie einen Request mit duplizierten Daten erhalten, werden diese zu einem Set eindeutiger Dinge konvertiert.

Und wann immer Sie diese Daten ausgeben, selbst wenn die Quelle Duplikate hatte, wird es als Set von eindeutigen Dingen ausgegeben.

Und es wird entsprechend annotiert/dokumentiert.

## Verschachtelte Modelle

Jedes Attribut eines Pydantic-Modells hat einen Typ.

### Preprocess the OpenAPI Specification for the Client Generator

The generated code still has some **duplicated information**.

We already know that this method is related to the **items** because that word is in the `ItemsService` (taken from the tag), but we still have the tag name prefixed in the method name too. 😕

## 0.9.1

* Document receiving [Multiple values with the same query parameter](https://fastapi.tiangolo.com/tutorial/query-params-str-validations/#query-parameter-list-multiple-values) and [Duplicate headers](https://fastapi.tiangolo.com/tutorial/header-params/#duplicate-headers). PR [#95](https://github.com/tiangolo/fastapi/pull/95).

## 0.9.0

* Upgrade compatible Pydantic version to `0.21.0`. PR [#90](https://github.com/tiangolo/fastapi/pull/90).