* Calling your dependency ("dependable") function with the correct parameters.
* Get the result from your function.
* Assign that result to the parameter in your *path operation function*.

```mermaid
graph TB

common_parameters(["common_parameters"])
read_items["/items/"]
read_users["/users/"]

common_parameters --> read_items
common_parameters --> read_users
```

!!! tip
    To declare File bodies, you need to use `File`, because otherwise the parameters would be interpreted as query parameters or body (JSON) parameters.

The files will be uploaded as "form data".

If you declare the type of your *path operation function* parameter as `bytes`, **FastAPI** will read the file for you and you will receive the contents as `bytes`.

* Ihre Abhängigkeitsfunktion („Dependable“) mit den richtigen Parametern aufzurufen.
* Sich das Ergebnis von dieser Funktion zu holen.
* Dieses Ergebnis dem Parameter Ihrer *Pfadoperation-Funktion* zuzuweisen.

```mermaid
graph TB

common_parameters(["common_parameters"])
read_items["/items/"]
read_users["/users/"]

common_parameters --> read_items
common_parameters --> read_users
```

          val message = record.message
          val parameters = record.parameters

          if (parameters != null && !message.startsWith("Raw") && !message.startsWith("Plaintext")) {
            if (verbose) {
              println(record.message)
              println(record.parameters[0])
            }

            // JSSE logs additional messages as parameters that are not referenced in the log message.

            clientEventsList.add(record.message)

            if (record.loggerName == "javax.net.ssl") {
              val parameters = record.parameters

              if (parameters != null) {
                clientEventsList.add(parameters.first().toString())
              }
            }
          }
        }
      }

      override fun flush() {
      }

      algorithmParameters,
      decompose = {
        listOf(
          it.algorithm,
          it.parameters,
        )
      },
      construct = {
        AlgorithmIdentifier(
          algorithm = it[0] as String,
          parameters = it[1],
        )
      },
    )

  /**
   * ```
   * BasicConstraints ::= SEQUENCE {

    ```

    as it will use that `None` as the default value, and that way make the parameter **not required**.

    The `Union[str, None]` part allows your editor to provide better support, but it is not what tells FastAPI that this parameter is not required.

Then, we can pass more parameters to `Query`. In this case, the `max_length` parameter that applies to strings:

```Python

**FastAPI** takes advantage of these type hints to do several things.

With **FastAPI** you declare parameters with type hints and you get:

* **Editor support**.
* **Type checks**.

...and **FastAPI** uses the same declarations to:

* **Define requirements**: from request path parameters, query parameters, headers, bodies, dependencies, etc.
* **Convert data**: from the request to the required type.

If you pass a "callable" as a dependency in **FastAPI**, it will analyze the parameters for that "callable", and process them in the same way as the parameters for a *path operation function*. Including sub-dependencies.

That also applies to callables with no parameters at all. The same as it would be for *path operation functions* with no parameters.

* The alternative documentation will also reflect the new query parameter and body:

![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png)

### Recap

In summary, you declare **once** the types of parameters, body, etc. as function parameters.

You do that with standard modern Python types.