OpenAPI schema omits zero numeric bounds for ListField child fields

[zainnadeem786]

Summary

OpenAPI schema generation appears to omit zero-valued numeric bounds for ListField child fields.

While investigating OpenAPI schema generation, I noticed that ListField child numeric constraints with a value of 0 are not included in the generated schema.

Reproduction

from rest_framework import serializers
from rest_framework.schemas.openapi import AutoSchema

class ExampleSerializer(serializers.Serializer):
    values = serializers.ListField(
        child=serializers.IntegerField(min_value=0)
    )

schema = AutoSchema()
result = schema.map_serializer(ExampleSerializer())

print(result)

Expected behavior

{
    "type": "array",
    "items": {
        "type": "integer",
        "minimum": 0
    }
}

Actual behavior

{
    "type": "array",
    "items": {
        "type": "integer"
    }
}

The zero-valued constraint is omitted.

Investigation

After tracing the OpenAPI schema generation flow, it appears the numeric bound mapping relies on truthiness checks, causing 0 and 0.0 to be skipped.

Top-level serializer fields appear to be corrected later through validator mapping, but nested/list child schemas do not receive the same correction.

Impact

Generated OpenAPI schemas may under-document validation constraints for list item values.

This affects schema accuracy rather than runtime validation.

Suggested fix

Use explicit None checks when mapping numeric bounds so that zero-valued constraints are preserved.

For example:

if field.min_value is not None:
    ...
if field.max_value is not None:
    ...

Suggested tests

• ListField(child=IntegerField(min_value=0))
• ListField(child=IntegerField(max_value=0))
• ListField(child=FloatField(min_value=0.0))
• ListField(child=FloatField(max_value=0.0))

I would be happy to prepare a PR with tests and a minimal fix if this behavior is considered a bug.

[browniebroke]

I see, yes that sounds like a bug. Assuming this is in DRF and not in drf-spectacular, fix would be appreciated, yes.

[zainnadeem786]

Thanks for confirming. @browniebroke

I verified this against DRF's OpenAPI schema generation and the issue appears to be caused by truthiness checks when mapping numeric bounds, which causes 0 and 0.0 values to be omitted for nested/list child fields.

I'll prepare a small PR with a minimal fix and regression tests covering IntegerField and FloatField min/max values set to zero.

[zainnadeem786]

Thanks for confirming the issue. @browniebroke

I've opened a PR with a minimal fix and regression tests:

#9977

The change updates the numeric bound mapping to use explicit None checks so that valid zero-valued constraints (0 and 0.0) are preserved in generated OpenAPI schemas for ListField child fields.

The PR also includes regression coverage for:

• IntegerField(min_value=0)
• IntegerField(max_value=0)
• FloatField(min_value=0.0)
• FloatField(max_value=0.0)

Feedback is welcome. Thanks for taking a look.