Customizing Serialization

use serde::{Deserialize, Serialize};
 
#[derive(Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
struct ApiUser {
    user_id: u64,
    #[serde(skip_serializing_if = "Option::is_none")]
    nickname: Option<String>,
    #[serde(default)]
    active: bool,
}

use serde::{Deserialize, Serialize};
 
#[derive(Serialize, Deserialize, Debug)]
#[serde(rename_all = "camelCase")]
struct User {
    user_id: u64,
    #[serde(skip_serializing_if = "Option::is_none")]
    display_name: Option<String>,
    #[serde(default)]
    role: String,
}
 
#[derive(Serialize, Deserialize, Debug)]
struct Envelope {
    #[serde(flatten)]
    user: User,
    version: u32,
}
 
fn main() {
    let u = User { user_id: 1, display_name: None, role: "member".into() };
    let json = serde_json::to_string(&u).unwrap();
    assert!(json.contains("userId"));
    assert!(!json.contains("displayName"));
 
    let env = Envelope { user: u, version: 2 };
    let flat = serde_json::to_string(&env).unwrap();
    assert!(flat.contains(r#""version":2"#));
    assert!(flat.contains(r#""userId":1"#));
}

mod ts {
    use serde::{Deserializer, Serializer};
    pub fn serialize<S: Serializer>(dt: &time::OffsetDateTime, s: S) -> Result<S::Ok, S::Error> {
        s.serialize_str(&dt.format(&time::format_description::well_known::Rfc3339).unwrap())
    }
}
#[serde(with = "ts")]
created_at: time::OffsetDateTime,