[REQ] "decimal" format is not supported for "number"

[ayushin]

The following schema:

  price:
    title: Price
    type: number
    format: decimal

generates a error, unknown format decimal for type number

Why not support it, converting to "number" type?

[Zomzog]

I don't see it in OAS3 data-type.

Does it really have to be supported?

[lemoinem]

This is definitely something that we'd need as well.
Supporting decimal types is a requirement for us, as we manipulate value that needs to be represented in base-10 to avoid (well-known) rounding issues.

Special care should be taken in the code generation templates to ensure the value is either never transformed in base-2 values (float/double in most language) or is exactly transformed back to base-10 value as soon as possible.

Regarding the presence of decimal in OAS3 data-type, there are many discussion around it (e.g., OAI/OpenAPI-Specification#845, https://github.com/OAI/OpenAPI-Specification/search?q=decimal&type=Issues).
The consensus seems present, only the format hasn't been integrated to the standard yet.

There are some discussions as to whether the format should be applied to strings or number type as well. In our case, it better fits to have it specified as number.

[siilats]

i submitted this PR #3910 that seems to work

[Kentalot]

Isn't the number type w/o a format just default to decimal?

[lemoinem]

The number type w/o a format defaults to float, (or double).
These are binary floating point arithmetic. Decimal implies decimal floating point arithmetic (or sometimes, decimal fixed point arithmetic)

[spacether]

I would love to have this feature in the python-experimental generator where one can send and receive python Decimals and they are sent as strings in json. Perhaps implemented in the same way as #3910

[alqh]

It looks like from the Data Types section

Data types in the OAS are based on the types supported by the JSON Schema Specification Draft 2019-09.

and JSON schema model defines number as

An arbitrary-precision, base-10 decimal number value, from the JSON "number" production

If I'm reading it correctly, wouldn't that mean number is decimal ?

[spacether]

My understanding is that this ticket is asking that the decimal type be sent as string in transmission to preserve sig figs. Most generators send numbers as floats in transmission though it depends upon the generator and the content-type of the payload.

[spacether]

Our project does support Decimals defined as:

type: string
format: number

Which focuses on the on-the wire definition of decimal as a string.
One can see this in our java files with the isDecimal property.

[spacether]

Decimal support has been added to the python-experimental generator in #11282

And here are some examples of it being used:

# a decimal model
m = DecimalPayload('12.34')
assert isinstance(m, DecimalPayload)
assert isinstance(m, DecimalSchema)
assert isinstance(m, str)
assert m == '12.34'
assert m.as_decimal == decimal.Decimal('12.34')

# an object model with a decimal property
price = Money(
    currency='usd',
    amount='10.99'
)
self.assertEqual(price.amount.as_decimal, decimal.Decimal('10.99'))
self.assertEqual(
    price,
    dict(currency='usd', amount='10.99')
)