Django FloatField is incorrectly labeled as float (32-bit) OpenAPI format rather than double (64-bit)

[johnthagen]

Consider a Django model:

class MyModel(Model):
    value = models.FloatField(null=True, blank=True)

From the Django docs

A floating-point number represented in Python by a float instance.

float's in Python are effectively always 64-bit double precision floats (it may be possible on some bespoke embedded platforms like MicroPython they are something else, but those are out of scope for Django usage).

But drf-spectacular, generates a schema for this FloatField of:

        value:
          type: number
          format: float
          nullable: true

According to the OpenAPI 3 spec, the correct format for this should be:

        value:
          type: number
          format: double
          nullable: true

It's likely many users have not hit this because some common client languages (e.g. Python and JavaScript/TypeScript) only have one float/number type so this would not have an impact on the generated client code.

However, a language such as C# does have two different floating point types, float and double. OpenAPI Generator using the csharp-netcore generator parses the drf-spectacular schema and uses 32-bit C# float instead of 64-bit double. This means that the client will lose precision that otherwise is stored in Django.

Example C# output:

        [DataMember(Name = "value", EmitDefaultValue = true)]
        public float? Value { get; set; }

Expected output:

        [DataMember(Name = "value", EmitDefaultValue = true)]
        public double? Value { get; set; }

[tfranzel]

Hey John,

excellent find! This must have slipped through the crack due to the imprecise naming.

CPython uses double internally and postgres, mysql and oracle Django DB adapters all map to double precision (https://github.com/django/django/blob/fac3dd7f390d372736e05974cc5c3ef1a3768fbb/django/db/backends/postgresql/base.py#L86)

So it makes sense to change the default mapping. One note however, format is a "free" field and you can put anything you want. OpenAPI deems it only informational. So not sure the code generator overreaches a bit in the case of c#.

[johnthagen]

@tfranzel Would it be possible to get a release with this fix?

[tfranzel]

@johnthagen it's coming very soon. just dealing with some loose ends.

[tfranzel]

closing this issue for now. feel free to comment if anything is missing or not working and we will follow-up.

[johnthagen]

Sorry for the late reply. I tested 0.22.0 and can confirm this issue is fixed!

Thanks! ❤️