Serde Serialization

Serde Standards

Basic Usage

use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug)]
struct User {
    id: u64,
    name: String,
    email: String,
    #[serde(default)]
    active: bool,
}

// Serialize to JSON
let user = User { id: 1, name: "Alice".into(), email: "a@b.com".into(), active: true };
let json = serde_json::to_string(&user)?;

// Deserialize from JSON
let user: User = serde_json::from_str(&json)?;

Field Attributes

#[derive(Serialize, Deserialize)]
struct Config {
    // Rename field in JSON
    #[serde(rename = "apiKey")]
    api_key: String,

    // Skip serializing if None
    #[serde(skip_serializing_if = "Option::is_none")]
    description: Option<String>,

    // Default value if missing
    #[serde(default = "default_timeout")]
    timeout_secs: u64,

    // Skip entirely
    #[serde(skip)]
    internal_state: bool,

    // Flatten nested struct
    #[serde(flatten)]
    metadata: Metadata,
}

fn default_timeout() -> u64 { 30 }

Enums

#[derive(Serialize, Deserialize)]
#[serde(tag = "type")]  // Tagged union
enum Event {
    #[serde(rename = "user_created")]
    UserCreated { id: u64, email: String },

    #[serde(rename = "user_deleted")]
    UserDeleted { id: u64 },
}

// Serializes as: {"type": "user_created", "id": 1, "email": "..."}

// Untagged variant
#[derive(Serialize, Deserialize)]
#[serde(untagged)]
enum Value {
    Integer(i64),
    Float(f64),
    String(String),
}

Custom Serialization

use serde::{Serializer, Deserializer};

#[derive(Serialize, Deserialize)]
struct Record {
    #[serde(serialize_with = "serialize_datetime")]
    #[serde(deserialize_with = "deserialize_datetime")]
    created_at: DateTime<Utc>,
}

fn serialize_datetime<S>(dt: &DateTime<Utc>, s: S) -> Result<S::Ok, S::Error>
where S: Serializer {
    s.serialize_str(&dt.to_rfc3339())
}

fn deserialize_datetime<'de, D>(d: D) -> Result<DateTime<Utc>, D::Error>
where D: Deserializer<'de> {
    let s = String::deserialize(d)?;
    DateTime::parse_from_rfc3339(&s)
        .map(|dt| dt.with_timezone(&Utc))
        .map_err(serde::de::Error::custom)
}

Format Support

Validation with Derive

use serde::Deserialize;
use validator::Validate;

#[derive(Deserialize, Validate)]
struct CreateUser {
    #[validate(length(min = 1, max = 100))]
    name: String,

    #[validate(email)]
    email: String,

    #[validate(range(min = 18, max = 120))]
    age: u8,
}

Best Practices

1. Deny unknown fields: #[serde(deny_unknown_fields)] for strict parsing
2. Rename all: #[serde(rename_all = "camelCase")] for consistent naming
3. Default trait: Implement Default for optional defaults
4. Error context: Use anyhow or custom errors for better messages
5. Performance: Use serde_json::from_slice for bytes, avoid string conversion

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