> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sqd.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Unions and typed JSON

> Model Squid SDK union types and typed JSON fields in schema.graphql — discriminate variants and store structured JSON in Postgres-backed entities.

Complex scalar types can be modelled using a typed JSON fields together with union types, making safe union types.

## Typed JSON

It is possible to define explicit types for JSON fields. The generated entity classes and the GraphQL API will respect the type definition of the field, enforcing the data integrity.

**Example**

```graphql theme={"system"}
type Entity @entity {
  a: A
}

type A {
  a: String
  b: B
  c: JSON
}

type B {
  a: A
  b: String
  e: Entity
}
```

## Union types

One can leverage union types supported both by [Typescript](https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#union-types) and [GraphQL](https://graphql.org/learn/schema/#union-types).  The union operator for `schema.graphql` supports only non-entity types, including typed JSON types described above. JSON types, however, are allowed to reference an entity type.

**Example**

```graphql theme={"system"}
type User @entity {
  id: ID!
  login: String!
}
        
type Farmer {
  user: User!
  crop: Int
}

type Degen {
  user: User!
  bag: String
}
        
union Owner = Farmer | Degen
        
type NFT @entity {
  name: String!
  owner: Owner!
}
```