django rest framework: set field-level error from serializer validate() method

Question

I have a serializer that validates fields based on the values of other fields, In the error response I would like to show each field error as a field error as opposed to showing

Answer 1

Similarly to the answer by @Jkk.jonah, this raises a ValidationError, but it reuses the original exception text without need to re-implement translations:

try:
    serializer.fields['field_val1'].fail('required')
except ValidationError as exc:
    raise ValidationError({
        'field_val1': exc.detail,
    })

By default (i.e. on rest_framework.fields.Field class), available keys are:

default_error_messages = {
    'required': _('This field is required.'),
    'null': _('This field may not be null.')
}

Subclasses can add their own error messages there (and Serializer is a subclass of Field).

BTW, new error messages will be automagically merged with existing (inherited) messages - won't be overridden as might be expected.