Unions in GraphQL

Introduction

In GraphQL, unions provide a way to define a field that can return different object types. This allows for a more flexible schema that can cater to various use cases.

What are Unions?

Unions in GraphQL are a special type that allows a field to return one of multiple possible types. Unlike interfaces, unions do not require the types to share any common fields.

Defining Unions in GraphQL

To define a union, use the union keyword followed by the union name and the types it can resolve to.

        union SearchResult = User | Post | Comment

        type User {
            id: ID!
            name: String!
        }

        type Post {
            id: ID!
            title: String!
        }

        type Comment {
            id: ID!
            content: String!
        }
        

Using Unions in Queries

When querying a union, you need to use inline fragments to specify which type you want to retrieve.

        query {
            search(text: "GraphQL") {
                ... on User {
                    id
                    name
                }
                ... on Post {
                    id
                    title
                }
                ... on Comment {
                    id
                    content
                }
            }
        }
        

Best Practices

• Keep union types to a minimum; too many types can complicate the schema.
• Use clear naming conventions for union types to convey their purpose.
• Document the possible types and their fields properly for better usability.

FAQ