Rust Enum from a String Union Field

Promoting a String Field to a serde-Aware Enum

When a JSON field always holds one of a fixed set of strings ("active", "inactive", "banned"), you can replace the generated String field with a Rust enum. The compiler then forces every match arm to be handled.

Example JSON

{
  "id": 1,
  "name": "Ada",
  "status": "active"
}

Generated Rust (initial)

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Root {
    pub id: i32,
    pub name: String,
    pub status: String,
}

Promoted to an enum

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum Status {
    Active,
    Inactive,
    Banned,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Root {
    pub id: i32,
    pub name: String,
    pub status: Status,
}

Why rename_all

Without #[serde(rename_all = "lowercase")], serde would expect the JSON to send "Active" (matching the variant name). Most APIs use lowercase or snake_case, so rename_all keeps the JSON contract intact while letting your Rust code use idiomatic PascalCase variants.

Other rename strategies

Attribute	JSON form
"lowercase"	active
"UPPERCASE"	ACTIVE
"snake_case"	active_user
"SCREAMING_SNAKE_CASE"	ACTIVE_USER
"kebab-case"	active-user

Variant aliases

If the API sends multiple spellings for the same logical value, use per-variant rename:

pub enum Role {
    #[serde(rename = "admin")]
    Administrator,
    #[serde(rename = "user", alias = "regular")]
    Regular,
}

Catching unknown values

Add a fallback variant to gracefully handle new server-side values:

#[serde(other)]
Unknown,

This prevents your client from crashing when the API adds a new status next quarter.