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GraphQL ships with scalars like Int, String, and Boolean. But real domains need more: a fixed set of statuses, a proper date type, or a validated email.

Enums and custom scalars let your schema express these precisely.

An enum restricts a field to a fixed list of named values. Clients can only send or receive one of those values, and tooling can offer autocompletion.

Reference the enum like any other type. The field is now guaranteed to hold a valid status.

Spring for GraphQL maps a schema enum to a Java enum automatically when the names match exactly.

The built-in scalars are limited. Representing a date as a String loses meaning and validation. A custom scalar defines how a domain value is serialized, deserialized, and validated.

First declare the scalar name in your SDL, then use it on fields.

The graphql-java-extended-scalars library provides ready-made scalars for DateTime, Date, URL, and more, so you do not write them by hand.

Wire the scalar into the runtime with a RuntimeWiringConfigurer bean so the schema knows how to handle it.

For a domain type you can define a GraphQLScalarType with a custom Coercing implementation controlling parse and serialize logic.

A scalar's Coercing can reject invalid input by throwing a CoercingParseValueException, giving you type-level validation for free.

Use these types wisely:

• Prefer enums over free-form strings for fixed sets
• Reuse library scalars before writing your own
• Keep Coercing logic pure and predictable
• Document each custom scalar's expected format

Test your knowledge of enums and scalars.

You extended your schema's type system:

• Enums restrict fields to a fixed value set
• They map automatically to Java enums by name
• Custom scalars model domain types like dates and emails
• Use library scalars or write a Coercing for your own
• Register scalars via RuntimeWiringConfigurer

Richer types make your API safer and more expressive.