Union Type Definition

A Union is an abstract type that simply enumerates other Object Types. The value of Union Type is actually a value of one of included Object Types.

Writing Union Types

In graphql-php union type is an instance of GraphQL\Type\Definition\UnionType (or one of its subclasses) which accepts configuration array in a constructor:

use GraphQL\Type\Definition\ObjectType;
use GraphQL\Type\Definition\UnionType;

$searchResultType = new UnionType([
    'name' => 'SearchResult',
    'types' => [
        MyTypes::story(),
        MyTypes::user()
    ],
    'resolveType' => function ($value): ObjectType {
        switch ($value->type ?? null) {
            case 'story': return MyTypes::story();
            case 'user': return MyTypes::user();
            default: throw new Exception("Unexpected SearchResult type: {$value->type ?? null}");
        }
    },
]);

This example uses inline style for Union definition, but you can also use
inheritance or schema definition language.

Configuration options

The constructor of UnionType accepts an array. Below is a full list of allowed options:

Option	Type	Notes
name	string	Required. Unique name of this interface type within Schema
types	array	Required. List of Object Types included in this Union. Note that you can't create a Union type out of Interfaces or other Unions.
description	string	Plain-text description of this type for clients (e.g. used by GraphiQL for auto-generated documentation)
resolveType	callback	function ($value, $context, ResolveInfo $info): ObjectType Receives $value from resolver of the parent field and returns concrete Object Type for this $value.