chrono_datetime_option_as_bson_datetime_option

helper.rs

pub mod chrono_datetime_option_as_bson_datetime_option {
    use bson::{ Bson, DateTime };
    use chrono::{ DateTime as ChronoDateTime, Utc };
    use serde::{ Deserialize, Deserializer, Serialize, Serializer };
    use std::result::Result;
    use serde::de::Error;

    pub fn deserialize<'de, D>(deserializer: D) -> Result<Option<ChronoDateTime<Utc>>, D::Error>
        where D: Deserializer<'de>
    {
        let bson = Bson::deserialize(deserializer)?;
        match bson {
            Bson::Null => Ok(None),
            Bson::DateTime(dt) => Ok(Some(dt.to_chrono())),
            _ => Err(D::Error::custom("expecting DateTime or Option<DateTime>")),
        }
    }

    pub fn serialize<S: Serializer>(
        val: &Option<ChronoDateTime<Utc>>,
        serializer: S
    ) -> Result<S::Ok, S::Error> {
        match val {
            None => serializer.serialize_none(),
            Some(val) => {
                let datetime = DateTime::from_chrono(*val);
                datetime.serialize(serializer)
            }
        }
    }
}

Available on crate feature chrono-0_4 only.

bson = { version = "*", features = ["chrono-0_4"] }
chrono = { version = "*", features = ["serde"] }

pub struct YourStruct {
 #[serde(default, with = "chrono_datetime_option_as_bson_datetime_option")]
 pub created_at: Option<DateTime<Utc>>,
}