In this video we look at union types in GraphQL and how they let you return different types from a single query. We'll build a search feature that returns both Authors and Books from one request using the SearchItem union type. We'll walk through defining the union in our schema, writing the controller that queries across multiple repositories and how Spring for GraphQL handles type resolution so the client knows exactly what type each result is.

📹 About this Course
In this series you'll learn how to build a GraphQL API from scratch using Spring Boot. We'll start with why GraphQL exists and work our way through schema design, data fetchers, performance optimization, observability and more. 

📦 GitHub Repository - GraphQL Books: https://github.com/danvega/graphql-books
📖 Spring for GraphQL Documentation: https://docs.spring.io/spring-graphql/reference/
🔧 GraphQL Java: https://www.graphql-java.com/
🚀 Spring Initializr: https://start.spring.io
📘 GraphQL Specification: https://spec.graphql.org

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Dan Vega

A walkthrough of GraphQL unions in the context of Java and Spring for GraphQL. Covers how to declare a union type in a GraphQL schema (e.g., SearchItem as either Author or Book), implement a search query controller that queries multiple repositories, and use the inline fragment syntax (... on TypeName) in GraphQL queries to request type-specific fields. Also demonstrates the __typename meta-field for identifying returned types at runtime.

GraphQL for Java Developers: 05 - Unions