Custom (de)serializers #782
Description
Thanks for making cynic: it's great!
I'm currently using it to talk to an API which works with non-rfc3339 timestamps (they look like: 2023-09-27T18:42:31 - note the lack of an offset at the end). I've added chrono::DateTime as a scalar type as per the docs:
cynic::impl_scalar!(chrono::DateTime<chrono::Utc>, schema::ISODateTime);But the lack of an offset makes chrono grumpy when parsing these values. Normally I'd handle this with a custom deserialize_with helper in serde. Something like:
fn generous_datetime_parser<'de, D>(
deserializer: D,
) -> Result<chrono::DateTime<chrono::Utc>, D::Error>
where
D: serde::Deserializer<'de>,
{
use serde::Deserialize;
let value = String::deserialize(deserializer)?;
chrono::DateTime::parse_from_rfc3339(value.as_str())
// Try adding a timezone (assume UTC) since those are often missing
.or_else(|_| chrono::DateTime::parse_from_rfc3339(format!("{}+00:00", &value).as_str()))
// Try adding a time component in case we were just given a date
.or_else(|_| {
chrono::DateTime::parse_from_rfc3339(format!("{}T00:00:00+00:00", &value).as_str())
})
.map_err(|e| {
serde::de::Error::custom(format!(
"Unable to parse chrono::DateTime from string ({}): {:?}",
value, e
))
})
.map(|dt| dt.with_timezone(&chrono::Utc))
}
...
#[derive(cynic::QueryFragment, Debug, serde::Serialize)]
#[cynic(schema = "my_schema")]
struct Foo {
#[serde(deserialize_with = "generous_datetime_parser")]
created: chrono::DateTime<chrono::Utc>,
}Using the deserialize_with serde option as above actually compiles, but it seems to do nothing, I'm guessing because of how cynic handles deserializing the scalar types internally. Is there already a supported way to do this in cynic, or at least a workaround to hook into the deserialization logic?