```

!!! warning
    Notice that `Field` is imported directly from `pydantic`, not from `fastapi` as are all the rest (`Query`, `Path`, `Body`, etc).

## Declare model attributes

You can then use `Field` with model attributes:

=== "Python 3.10+"

    ```Python hl_lines="11-14"
    {!> ../../../docs_src/body_fields/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="11-14"

@needs_pydanticv2
def test_get_model_config():
    # For coverage in Pydantic v2
    class Foo(BaseModel):
        model_config = ConfigDict(from_attributes=True)

    foo = Foo()
    config = _get_model_config(foo)
    assert config == {"from_attributes": True}


def test_complex():
    app = FastAPI()

    @app.post("/")
    def foo(foo: Union[str, List[int]]):
        return foo

body:
  - type: markdown
    attributes:
      value: |
        Thanks for your interest in FastAPI! 🚀

        If you are not @tiangolo or he didn't ask you directly to create an issue here, please start the conversation in a [Question in GitHub Discussions](https://github.com/tiangolo/fastapi/discussions/categories/questions) instead.
  - type: checkboxes
    id: privileged
    attributes:
      label: Privileged issue

    assert response.status_code == 422, response.text
    assert response.json() == IsDict(
        {
            "detail": [
                {
                    "type": "model_attributes_type",
                    "loc": ["body"],
                    "msg": "Input should be a valid dictionary or object to extract fields from",
                    "input": "name=Foo&price=50.5",
                }

    assert response.status_code == 422, response.text
    assert response.json() == IsDict(
        {
            "detail": [
                {
                    "type": "model_attributes_type",
                    "loc": ["body"],
                    "msg": "Input should be a valid dictionary or object to extract fields from",
                    "input": "name=Foo&price=50.5",
                }

# Reference - Code API

Here's the reference or code API, the classes, functions, parameters, attributes, and
all the FastAPI parts you can use in your applications.

If you want to **learn FastAPI** you are much better off reading the

* `tags: List[str] = []` has a default of an empty list: `[]`.

but you might want to omit them from the result if they were not actually stored.

For example, if you have models with many optional attributes in a NoSQL database, but you don't want to send very long JSON responses full of default values.

### Use the `response_model_exclude_unset` parameter

      required: true
  - type: dropdown
    id: os
    attributes:
      label: Operating System
      description: What operating system are you on?
      multiple: true
      options:
        - Linux
        - Windows
        - macOS
        - Other
    validations:
      required: true
  - type: textarea
    id: os-details
    attributes:
      label: Operating System Details

=== "Python 3.8+"

    ```Python hl_lines="9-11"
    {!> ../../../docs_src/body_nested_models/tutorial004.py!}
    ```

### Das Kindmodell als Typ verwenden

Und dann können wir es als Typ eines Attributes verwenden.

=== "Python 3.10+"

    ```Python hl_lines="18"
    {!> ../../../docs_src/body_nested_models/tutorial004_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="20"

            div.innerHTML = `<span ${this._attributes(line)}>${line.value || ''}</span>`;

            return div.firstElementChild;
        });
    }

    /**
     * Helper function for generating attributes string.
     *
     * @param {Object} line - Line data object.
     * @returns {string} - String of attributes.
     */
    _attributes(line) {
        let attrs = '';