SchemaCompanionVersionSpecific

Derives the schema of A at compile time. It supports case classes and other classes whose constructor parameters are vals or vars, sealed traits and sealed abstract classes with their cases, case objects, options, arrays and collections, and ZIO Prelude newtypes. On Scala 3 it also supports enums, union types, generic and named tuples, opaque types and Neotype newtypes, and derives Schema calls it.

For each field or case type it uses the implicit Schema in scope when there is one, so an implicit val of type Schema[LocalDate] changes how every LocalDate field is represented, in every format. An implicit codec in scope, such as a JsonCodec, is not used. Annotations that extend Modifier.Term on fields and cases, and Modifier.Reflect on the type, become modifiers of the schema.

Derivation fails to compile for a type it cannot derive (Cannot derive schema for ...), and for a field marked transient or encodeTransient that has no default value and is neither an Option nor a collection.

Deriving, from inside a class, a sealed trait declared in that class whose case classes sit in the trait's companion crashes the compiler. Derive the trait's schema in its companion instead, or declare the model in an object.

sealed trait Format
object Format {
 case object Hardcover                  extends Format
 final case class Ebook(sizeMb: Double) extends Format
 implicit val schema: Schema[Format] = Schema.derived
}

final case class Book(format: Format, title: String)
object Book {
 implicit val schema: Schema[Book] = Schema.derived
}

val json = Schema[Book].jsonCodec.encodeToString(Book(Format.Ebook(2.5), "Zionomicon"))
// {"format":{"Ebook":{"sizeMb":2.5}},"title":"Zionomicon"}