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 { #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`:

You can use the same type declarations with `str`, `float`, `bool` and many other complex data types.

Several of these are explored in the next chapters of the tutorial.

## Order matters { #order-matters }

### Based on open standards { #based-on-open-standards }

* <a href="https://github.com/OAI/OpenAPI-Specification" class="external-link" target="_blank"><strong>OpenAPI</strong></a> for API creation, including declarations of <abbr title="also known as: endpoints, routes">path</abbr> <abbr title="also known as HTTP methods, as POST, GET, PUT, DELETE">operations</abbr>, parameters, request bodies, security, etc.

But you can re-order them, and have the value without a default (the query parameter `q`) first.

It doesn't matter for **FastAPI**. It will detect the parameters by their names, types and default declarations (`Query`, `Path`, etc), it doesn't care about the order.

So, you can declare your function as:

//// tab | Python 3.8 non-Annotated

/// tip

Prefer to use the `Annotated` version if possible.

///

We could do better.

We can declare a `UserBase` model that serves as a base for our other models. And then we can make subclasses of that model that inherit its attributes (type declarations, validation, etc).

All the data conversion, validation, documentation, etc. will still work as normally.

Then I contributed to it, to make it fully compliant with JSON Schema, to support different ways to define constraint declarations, and to improve editor support (type checks, autocompletion) based on the tests in several editors.

        @SuppressWarnings("nullness")
        Object[] result = standardToArray();
        return result;
      }

      @Override
      @SuppressWarnings("nullness") // b/192354773 in our checker affects toArray declarations
      public <T extends @Nullable Object> T[] toArray(T[] array) {
        return standardToArray(array);
      }
    };
  }

  @Override
  @CanIgnoreReturnValue

```Python
my_list: list[str]
```

In versions of Python before 3.9, it would be:

```Python
from typing import List

my_list: List[str]
```

That's all standard Python syntax for type declarations.

Use that same standard syntax for model attributes with internal types.

So, in our example, we can make `tags` be specifically a "list of strings":

     * non-reified type or has bounds, {@code forDependants} is used to do further resolution, which
     * doesn't try to resolve any type variable on generic declarations that are already being
     * resolved.
     *
     * <p>Should only be called and overridden by {@link #resolve(TypeVariable)}.
     */
    Type resolveInternal(TypeVariable<?> var, TypeTable forDependants) {

///

## Integrated with OpenAPI { #integrated-with-openapi }

All the request declarations, validations and requirements of your dependencies (and sub-dependencies) will be integrated in the same OpenAPI schema.

So, the interactive docs will have all the information from these dependencies too: