Choices and blank=True

[jayvdb]

Describe the bug
When there is a charfield with choices, and blank=True, the empty string ('') is a valid value, unrelated to the field being required or not, or nullable or not.

However drf-spectacular creates an enum of the choices without an option for the empty string.

To Reproduce
django-oscar-api UserAddressSerializer, BillingAddressSerializer, ShippingAddressSerializer, all include a title that has a choices of Mr, Mrs, Dr, etc, and blank=True

Expected behavior
The enum needs to include the empty string, or some other schema structure that allows the empty string.

IMO it would be preferrable that the enum in components doesnt include the empty string, as this would mean two fields using the same choices but different blank values would require two enums. And having two enums would result in more clashes, component renames, and those enum names are now appearing in peoples ENUM_NAME_OVERRIDES .

[tfranzel]

oh thats a tricky one. you are absolutely right about the possible duplication. on the other hand it is a valid input. we have to investigate how to solve that in the least invasive way.

[tfranzel]

sry that commit is unrelated. typed the wrong number

[tfranzel]

@jayvdb not sure if you were notified of the mention in the PR. would be awesome if you could check out the solution proposal.

[gabn88]

I'm not sure if this is related, but when using CharField choices and blank=True, the '' (which is valid to set it empty) does not come up in the Enum that is created.

@tfranzel Do you have any suggestion on how to circumvent this?

[tfranzel]

@gabn88 please re-check. this is heavily tested and should work, if 'ENUM_ADD_EXPLICIT_BLANK_NULL_CHOICE': True, (the default)

It will however not be part of the enum, as it belongs to the field and not the enum itself. You might use that enum with AND without the blank, and thus is has to be combined:

drf-spectacular/tests/test_postprocessing.yml

Lines 55 to 60 in aeca119

	language:
	nullable: true
	oneOf:
	- $ref: '#/components/schemas/LanguageEnum'
	- $ref: '#/components/schemas/BlankEnum'
	- $ref: '#/components/schemas/NullEnum'

this will be performed for model blank, serializer allow_blank, and explicit mention of '' in the choices. If you find a bug, please open a new issue. thx