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.

# Query Parameter Models

If you have a group of **query parameters** that are related, you can create a **Pydantic model** to declare them.

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

## Query Parameters with a Pydantic Model

     * Set the value of hostname, used in parameter comment. <br>
     * Even if empty string, treated as empty plainly. So "IF pmb != null" is false if empty.
     * @param hostname The parameter value of hostname. (NotNull)
     */
    public void setHostname(String hostname) {
        registerVariable("hostname", hostname);
    }

    /**
     * Set the value of jobname, used in parameter comment. <br>

        </field>
      </fields>
    </class>

    <class xdoc.anchorName="parameter">
      <name>Parameter</name>
      <version>1.0.0+</version>
      <description>A parameter description.</description>
      <!-- see o.a.m.plugin.descriptor.Parameter -->
      <fields>
        <field>
          <name>name</name>
          <version>1.0.0+</version>

```

## Metadaten für Tags

Sie können mit dem Parameter `openapi_tags` auch zusätzliche Metadaten für die verschiedenen Tags hinzufügen, die zum Gruppieren Ihrer Pfadoperationen verwendet werden.

Es wird eine Liste benötigt, die für jedes Tag ein Dict enthält.

Jedes Dict kann Folgendes enthalten:

* `name` (**erforderlich**): ein `str` mit demselben Tag-Namen, den Sie im Parameter `tags` in Ihren *Pfadoperationen* und `APIRouter`n verwenden.

    assertEquals("utf-8", mediaType.parameter("charset"))
    assertEquals("1", mediaType.parameter("a"))
    assertEquals("2", mediaType.parameter("b"))
    assertEquals("3", mediaType.parameter("c"))
    assertEquals("utf-8", mediaType.parameter("CHARSET"))
    assertEquals("1", mediaType.parameter("A"))
    assertEquals("2", mediaType.parameter("B"))
    assertEquals("3", mediaType.parameter("C"))
  }

# Body - Multiple Parameters

Now that we have seen how to use `Path` and `Query`, let's see more advanced uses of request body declarations.

## Mix `Path`, `Query` and body parameters

First, of course, you can mix `Path`, `Query` and request body parameter declarations freely and **FastAPI** will know what to do.

And you can also declare body parameters as optional, by setting the default to `None`:

//// tab | Python 3.10+

{!> ../../docs_src/query_params/tutorial002.py!}
```

////

In this case, the function parameter `q` will be optional, and will be `None` by default.

/// check

Also notice that **FastAPI** is smart enough to notice that the path parameter `item_id` is a path parameter and `q` is not, so, it's a query parameter.

///

## Query parameter type conversion

You can also declare `bool` types, and they will be converted:

      pos = value.indexOfElement("=,;", pos)
      val directive = value.substring(tokenStart, pos).trim()
      val parameter: String?

      if (pos == value.length || value[pos] == ',' || value[pos] == ';') {
        pos++ // Consume ',' or ';' (if necessary).
        parameter = null
      } else {
        pos++ // Consume '='.
        pos = value.indexOfNonWhitespace(pos)

        router_sig = inspect.signature(router_method)
        app_sig = inspect.signature(app_method)
        param: inspect.Parameter
        for key, param in base_sig.parameters.items():
            router_param: inspect.Parameter = router_sig.parameters[key]
            app_param: inspect.Parameter = app_sig.parameters[key]
            assert param.annotation == router_param.annotation
            assert param.annotation == app_param.annotation