fix: openapi schema for literal and enum unions with None.

[peterschutt]

Pull Request Checklist

• New code has 100% test coverage
• (If applicable) The prose documentation has been updated to reflect the changes introduced by this PR
• (If applicable) The reference documentation has been updated to reflect the changes introduced by this PR
• Pre-Commit Checks were ran and passed
• Tests were ran and passed

Description

Existing behavior is to make the schema for every type that is a union with None a "one_of" schema, that includes OpenAPIType.NULL in the "one_of" types.

litestar/litestar/_openapi/schema_generation/schema.py

Lines 319 to 340 in 5db8d81

	def for_optional_field(self, field_definition: FieldDefinition) -> Schema:
	"""Create a Schema for an optional FieldDefinition.
	Args:
	field_definition: A signature field instance.
	Returns:
	A schema instance.
	"""
	schema_or_reference = self.for_field_definition(
	FieldDefinition.from_kwarg(
	annotation=make_non_optional_union(field_definition.annotation),
	name=field_definition.name,
	default=field_definition.default,
	)
	)
	if isinstance(schema_or_reference, Schema) and isinstance(schema_or_reference.one_of, list):
	result = schema_or_reference.one_of
	else:
	result = [schema_or_reference]
	return Schema(one_of=[Schema(type=OpenAPIType.NULL), *result])

When a Literal or Enum type is in a union with None, this behavior is not desirable, as we want to have null available in the list of available options on the type's schema.

This PR changes literal and enum schema generation so that it can be identified that the types are in a union with None, allowing null to be included in Schema.enum values.

Close Issue(s)

Closes #2546

[JacobCoffee]

Im going to try this out at work since i hit this issue

[JacobCoffee]

Running with field: Enum | None works well, extra none option, and execute works. But without | None im hitting this still?

{
  "status_code": 400,
  "detail": "Validation failed for GET http://127.0.0.1:8000/",
  "extra": [
    {
      "message": "Expected `str`, got `null`",
      "key": "environment",
      "source": "query"
    }
  ]
}

[peterschutt]

Running with field: Enum | None works well, extra none option, and execute works. But without | None im hitting this still?

{

  "status_code": 400,

  "detail": "Validation failed for GET http://127.0.0.1:8000/",

  "extra": [

    {

      "message": "Expected `str`, got `null`",

      "key": "environment",

      "source": "query"

    }

  ]

}

Is this with default=None still declared in Parameter?

[provinzkraut]

Running with field: Enum | None works well, extra none option, and execute works. But without | None im hitting this still?

{
  "status_code": 400,
  "detail": "Validation failed for GET http://127.0.0.1:8000/",
  "extra": [
    {
      "message": "Expected `str`, got `null`",
      "key": "environment",
      "source": "query"
    }
  ]
}

Can you elaborate? If it's not | None then that error seems to be correct?

[provinzkraut]

Good stuff, just some nits you can feel free to ignore :)

[sonarqubecloud]

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[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/litestar-docs-preview/2550