Unions

A union type represents a set of object types. It is very similar to an interface, except that there is no requirement for common fields between the specified types.

SDL

type TextContent {
  text: String!
}

type ImageContent {
  imageUrl: String!
  height: Int!
}

union PostContent = TextContent | ImageContent

Clients can query fields returning a union like the following.

GraphQL

{
  postContent {
    ... on TextContent {
      text
    }
    ... on ImageContent {
      imageUrl
    }
  }
}

Learn more about unions here.

Usage

Unions can be defined like the following.

We can use a marker interface to define object types as part of a union.

[UnionType("PostContent")]
public interface IPostContent
{
}

public class TextContent : IPostContent
{
    public string Text { get; set; }
}

public class ImageContent : IPostContent
{
    public string ImageUrl { get; set; }

    public int Height { get; set; }
}

public class Query
{
    public IPostContent GetContent()
    {
        // Omitted code for brevity
    }
}

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services
            .AddGraphQLServer()
            .AddQueryType<Query>()
            .AddType<TextContent>()
            .AddType<ImageContent>();
    }
}

Last updated on 2021-06-02 by Tobias Tengler