# Sub-dependencies

You can create dependencies that have **sub-dependencies**.

They can be as **deep** as you need them to be.

**FastAPI** will take care of solving them.

## First dependency "dependable"

You could create a first dependency ("dependable") like:

//// tab | Python 3.10+

```Python hl_lines="8-9"
{!> ../../docs_src/dependencies/tutorial005_an_py310.py!}
```

////

//// tab | Python 3.9+

Let's first focus on the dependency.

It is just a function that can take all the same parameters that a *path operation function* can take:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

That's it.

**2 lines**.

And it has the same shape and structure that all your *path operation functions* have.

```JSON
{
    "item": {
        "name": "Foo",
        "description": "The pretender",
        "price": 42.0,
        "tax": 3.2
    },
    "user": {
        "username": "dave",
        "full_name": "Dave Grohl"
    }
}
```

/// note

Notice that even though the `item` was declared the same way as before, it is now expected to be inside of the body with a key `item`.

///

///

/// check

You don't have to worry about performance when including routers.

This will take microseconds and will only happen at startup.

So it won't affect performance. ⚡

///

### Include an `APIRouter` with a custom `prefix`, `tags`, `responses`, and `dependencies`

Now, let's imagine your organization gave you the `app/internal/admin.py` file.

				continue
			}
			wk.Take()
			go func() {
				defer wk.Give()

				stopFn := globalBatchJobsMetrics.trace(batchJobMetricReplication, job.ID, attempts)
				success := true
				if err := r.ReplicateToTarget(ctx, api, c, result, retry); err != nil {
					if miniogo.ToErrorResponse(err).Code == "PreconditionFailed" {
						// pre-condition failed means we already have the object copied over.
						return

     * on his discretion, e.g. via the {@code -Dkey=value} parameter on the command line.
     *
     * @return The user properties, never {@code null}.
     */
    Properties getUserProperties();

    /**
     * Sets the user properties to use for interpolation. The user properties have been configured directly by the user

    assertEquals("XheXXuickXXrownXXoxX", builder.build().escape("The Quick Brown Fox!"));
    // Explicit replacements take priority over unsafe characters.
    builder.addEscape(' ', "_");
    builder.addEscape('!', "_");
    assertEquals("Xhe_Xuick_Xrown_Xox_", builder.build().escape("The Quick Brown Fox!"));
    // Explicit replacements take priority over safe characters.
    builder.setSafeRange(' ', '~');

### `response_model` Priority

If you declare both a return type and a `response_model`, the `response_model` will take priority and be used by FastAPI.

This way you can add correct type annotations to your functions even when you are returning a type different than the response model, to be used by the editor and tools like mypy. And still you can have FastAPI do the data validation, documentation, etc. using the `response_model`.

Each of those response `dict`s can have a key `model`, containing a Pydantic model, just like `response_model`.

**FastAPI** will take that model, generate its JSON Schema and include it in the correct place in OpenAPI.

```Python
{
    "name": "Barz",
    "price": 3,
    "description": None,
}
```

because it doesn't include the already stored attribute `"tax": 20.2`, the input model would take the default value of `"tax": 10.5`.

And the data would be saved with that "new" `tax` of `10.5`.

## Partial updates with `PATCH`