Add OpenAPI-support for rust_decimal?

[Christoph-AK]

Hey there,
I would love to directly deserialize incoming API requests into rust_decimal::Decimal without precision loss.

Currently with

use rust_decimal::Decimal;

/// Get recipe resource link
#[derive(Object)]
pub struct GetRecipeResourceLink {
    resource: String,
    relative_amount: Decimal,
}

I get the trait bound 'rust_decimal::Decimal: poem_openapi::types::Type' is not satisfied.

Can compatibility for this be added? Maybe behind a feature gate, like in mysql_common?

[Christoph-AK]

@sunli829 Thanks so much for the quick implementation!

Two observations:

1. Could you change the serialisation from to_string to normalize? This will give cleaner responses.
2. Less importantly: I wonder if we can somehow make this a json Number instead of a String. I understand that on one hand while initially parsing a json-string into the json value dictionary some loss of precision could already occur, as the json number is most likely represented as float internally, so letting the value stay a string is possibly the only way to keep complete accuracy. On the other hand this way we lose type safety and compatibility with calling js here - annoying. For now with the normalization this should be good enough and keeping the precision is by far most important, but maybe someone will find a better way to represent this. Or maybe make this accept both a string and a number for now, but output as string only?