Field Types

Field Type Overview¶

Every field has a type.

type Example {
  name string
  count int
}

VDL supports:

• primitive types
• custom types
• enums
• arrays
• maps
• inline objects

Primitive Types¶

Example:

type PrimitiveExample {
  name string
  age int
  score float
  active bool
  createdAt datetime
}

Custom Types¶

Fields can reference other declared types.

type Address {
  city string
  country string
}

type User {
  id string
  address Address
}

Enum Fields¶

Fields can reference enums.

enum OrderStatus {
  Pending
  Paid
  Shipped
}

type Order {
  id string
  status OrderStatus
}

Arrays¶

Arrays use [] after the element type.

type Collection {
  tags string[]
  scores int[]
  orders Order[]
}

type Order {
  id string
}

Multidimensional arrays repeat the suffix:

type MatrixData {
  values float[][]
}

Maps¶

Maps use map[T], where T is the value type.

type Metrics {
  counters map[int]
  labels map[string]
}

Maps can contain custom types:

type User {
  id string
  email string
}

type UserDirectory {
  usersById map[User]
}

Maps can also contain arrays or nested maps:

type ComplexMapExample {
  tagsByGroup map[string[]]
  matrixByName map[float[][]]
}

Inline Objects¶

Inline objects are anonymous structured field types.

type SearchResult {
  id string
  metadata {
    score float
    source string
  }
}

Use inline objects when the nested shape does not need a reusable name.

Use a named type when the shape is reused or important enough to document on its own.

Optional Field Types¶

Optionality belongs to the field name, not the type.

type User {
  displayName? string
  tags? string[]
  profile? {
    bio? string
  }
}

The ? always appears after the field name.

Recursive Types¶

VDL can model recursive structures when a cycle is broken by an optional field.

type TreeNode {
  id string
  children? TreeNode[]
}

Direct required cycles are rejected because they cannot be represented as finite data.

Invalid:

type A {
  b B
}

type B {
  a A
}

Make one side optional to model a nullable or absent link.