Enums and Interfaces

What you'll walk away with

Explain the core ideas behind Enums and Interfaces
Run the sample GraphQL query or code and verify its output
Apply the technique correctly to the Tutorial Platform and production scenarios

Build the mental model

An `enum` restricts a field to an exact set of allowed values, catching typos at the validation level instead of at runtime. An `interface` is a contract that lets multiple object types share common fields (such as `id` and `title`); a type promises to implement every interface field using the `implements` keyword. Clients can query interface fields and get common data even without knowing the concrete type.

Connect it to a real scenario

Define a `Difficulty` enum with `BEGINNER | INTERMEDIATE | ADVANCED` and use it on `Tutorial.difficulty`. Declare a `Content` interface with `id` and `title`, and have both `Tutorial` and `Exercise` implement it, so a homepage search-result list can render both content types through the same shared fields.

Enums fix a value set, catching typos at validation time
Interfaces are a contract for fields shared across types
`implements` commits a type to every interface field

Try the working example

graphql

enum Difficulty {
  BEGINNER
  INTERMEDIATE
  ADVANCED
}

interface Content {
  id: ID!
  title: String!
}

type Tutorial implements Content {
  id: ID!
  title: String!
  difficulty: Difficulty!
}

type Exercise implements Content {
  id: ID!
  title: String!
  points: Int!
}

You should see

You can write enums and interfaces and share fields across types in a schema.

5-minute try-it

Write a `Status` enum (`DRAFT | PUBLISHED | ARCHIVED`) and add a `status: Status!` field to `Tutorial`.

One important caution

Changing an interface field's shape in an implementing type (rather than only narrowing return type covariantly) causes a schema validation error.

GraphQL — Schemas and Types — GraphQL

Easy traps

Changing an interface field's shape in an implementing type (rather than only narrowing return type covariantly) causes a schema validation error.
Validate sample queries and mutations on a local or test server with recoverable data before applying them to production.

Exercise

Write a `Status` enum (`DRAFT | PUBLISHED | ARCHIVED`) and add a `status: Status!` field to `Tutorial`.

You'll know it worked when: You can write enums and interfaces and share fields across types in a schema.