Attributes

Add format, language, validation, and lifecycle information to a model.

An attribute is metadata attached to a schema element. The type structure says what values exist; attributes tell tools how to represent, validate, or document those values.

Built-in attribute plugins parse known attributes into typed metadata. Generators consume that metadata. An attribute’s effect therefore depends on the generator and any enabled generator plugins.

Attach Attributes

Attributes precede the definition, field, or case they describe:

#[json(rename_all = "snake_case")]
record User {
    #[json(name = "name")]
    display_name: string,

    #[validate({ 1 <= _.size <= 64 })]
    username: string,
}

This record uses snake_case JSON keys, overrides one key to name, and places a size rule on username. The rule produces runtime validation only when a supported validation plugin is enabled.

Schema-level attributes use #![...]:

#![unstable(note = "This schema is being revised.")]

Attribute Arguments

Arguments can be flags, assignments, nested lists, paths, or token bodies:

#[json(tagged = externally)]
#[rust(derive(Clone, Debug))]
#[validate({ 0 <= _ <= 100 }, message = "Use a value from 0 to 100.")]

Strings are quoted. Path values such as externally and type references such as User are not. The { ... } body of a validation rule is parsed by the validation expression engine.

Several attributes can apply to one element. Repeated validate attributes create separate rules; Rust’s derive and attr arguments accumulate.

Choose an Attribute Family

The attribute reference lists accepted arguments and targets. For custom metadata, see extending Sidex.