## Use the instance as a dependency { #use-the-instance-as-a-dependency }

Then, we could use this `checker` in a `Depends(checker)`, instead of `Depends(FixedContentQueryChecker)`, because the dependency is the instance, `checker`, not the class itself.

And when solving the dependency, **FastAPI** will call this `checker` like:

```Python
checker(q="somequery")
```

### Exception Handling
```java
import org.codelibs.core.exception.*;

// Runtime exception wrappers eliminate try-catch boilerplate
try {
    // Code that might throw checked exceptions
    return ClassUtil.newInstance(className); // Wraps checked exceptions automatically
} catch (ClassNotFoundRuntimeException e) {
    // Handle the wrapped exception
    logger.error("Class not found: " + className, e);
}
```

				iamLogIf(ctx, logErr)
			}
		}
	}
	return skipped, nil
}

// CheckKey validates the incoming accessKey
func (sys *IAMSys) CheckKey(ctx context.Context, accessKey string) (u UserIdentity, ok bool, err error) {
	if !sys.Initialized() {
		return u, false, nil
	}

	if accessKey == globalActiveCred.AccessKey {

These custom validators are for things that can be checked with **only** the **same data** provided in the request.

///

### Understand that Code { #understand-that-code }

    * Use of hierarchical Pydantic models, Python `typing`’s `List` and `Dict`, etc.
    * And validators allow complex data schemas to be clearly and easily defined, checked and documented as JSON Schema.
    * You can have deeply **nested JSON** objects and have them all validated and annotated.
* **Extensible**:

But you might want to still keep the return type annotation in the function to get the support from tools like editors and type checkers (e.g. mypy).

In this case, you can disable the response model generation by setting `response_model=None`:

{* ../../docs_src/response_model/tutorial003_05_py310.py hl[7] *}

on:
  # For Branch-Protection check. Only the default branch is supported. See
  # https://github.com/ossf/scorecard/blob/main/docs/checks.md#branch-protection
  branch_protection_rule:
  # To guarantee Maintained check is occasionally updated. See
  # https://github.com/ossf/scorecard/blob/main/docs/checks.md#maintained
  schedule:
    - cron: '45 9 * * 0'
  push:
    branches: [ "master" ]

# Declare default permissions as read only.

on:
  # For Branch-Protection check. Only the default branch is supported. See
  # https://github.com/ossf/scorecard/blob/main/docs/checks.md#branch-protection
  branch_protection_rule:
  # To guarantee Maintained check is occasionally updated. See
  # https://github.com/ossf/scorecard/blob/main/docs/checks.md#maintained
  schedule:
    - cron: '26 3 * * 2'
  push:
    branches: [ "master" ]

# Declare default permissions as read only.

{* ../../docs_src/body_nested_models/tutorial005_py310.py hl[2,8] *}

The string will be checked to be a valid URL, and documented in JSON Schema / OpenAPI as such.

## Attributes with lists of submodels { #attributes-with-lists-of-submodels }

You can also use Pydantic models as subtypes of `list`, `set`, etc.:

	e.encoder = func() reedsolomon.Encoder {
		once.Do(func() {
			e, err := reedsolomon.New(dataBlocks, parityBlocks, reedsolomon.WithAutoGoroutines(int(e.ShardSize())))
			if err != nil {
				// Error conditions should be checked above.
				panic(err)
			}
			enc = e
		})
		return enc
	}
	return
}

// EncodeData encodes the given data and returns the erasure-coded data.
// It returns an error if the erasure coding failed.