In some circumstances a Validator class or a Default class may need to access the serializer field with which it is called, or the `.context` with which the serializer was instantiated. In particular:
* Uniqueness validators need to be able to determine the name of the field to which they are applied, in order to run an appropriate database query.
* The `CurrentUserDefault` needs to be able to determine the context with which the serializer was instantiated, in order to return the current user instance.
Previous our approach to this was that implementations could include a `set_context` method, which would be called prior to validation. However this approach had issues with potential race conditions. We have now move this approach into a pending deprecation state. It will continue to function, but will be escalated to a deprecated state in 3.12, and removed entirely in 3.13.
Instead, validators or defaults which require the serializer context, should include a `requires_context = True` attribute on the class.
The `__call__` method should then include an additional `serializer_field` argument.
Validator implementations will look like this:
```python
class CustomValidator:
requires_context = True
def __call__(self, value, serializer_field):
...
```
Default implementations will look like this:
```python
class CustomDefault:
requires_context = True
def __call__(self, serializer_field):
...
```
---
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