OpenAPI: Trying to make a `time::OffsetDateTime` `#[oai(read_only)]` requires it to be Default-able, when it isn't

[lyssieth]

I'm trying to create a type that contains a time::OffsetDateTime, but trying to derive Object on it with the time field being #[oai(read_only)] (since it's determined by the server) fails to compile.

I'm unsure whether I'm doing everything as expected by the API, or in general correctly.

Expected Behavior

Compiling as expected, without any warnings

Actual Behavior

error[E0277]: the trait bound time::OffsetDateTime: std::default::Default is not satisfied

Steps to Reproduce the Problem

# Cargo.toml (partial)
poem-openapi = { version = "3.0.4", features = ["time"] }
time = "0.3.28"

// src/lib.rs
use poem_openapi::Object;
use time::OffsetDateTime;

#[derive(Object)]
#[oai(read_only_all)]
struct Reproduction {
    time: OffsetDateTime,
}

And then trying to compile.

Specifications

• Version:
  • poem-openapi v. 3.0.4
  • time v. 0.3.28
• Platform: Linux (toolchain stable-x86_64-unknown-linux-gnu), but likely affects all
• Subsystem: poem-openapi

[sunli829]

It's not a bug, if you set this field to read-only, then this object will be given a default value (via Default::default) when used as a request, you may consider create a newtype MyOffsetDateTime, and implement Default::default for it.

[lyssieth]

Huh. That's definitely a bit strange, but I can understand it.

Is there a better way to handle a type that will only ever be returned from the server, and can't be sent to the server, then?

[sunli829]

In v3.0.6 can use default to specify a function that creates a default value, which is more convenient than defining a newtype.

fn default_offset_datetime() -> OffsetDateTime {
    OffsetDateTime::now_utc()
}

#[derive(Debug, Object, PartialEq)]
struct Obj {
    #[oai(read_only, default = "default_offset_datetime")]
    time: OffsetDateTime,
}

I'll let you know when v3.0.5 is released. 🙂

[lyssieth]

Alright, thank you! I'll be keeping a keen eye out :>