This article covers best practices for designing schemas in AWS AppSync Merged APIs, which combine multiple GraphQL APIs into a unified interface.

• Design Source APIs as independent microservices handling single domains with clear ownership
• Define primary keys for each type to enable data relationships across Source APIs
• Establish relationships between Source APIs using foreign keys for data joining
• Document relationships through schema comments for developer clarity
• Design Merged APIs for organization-wide use cases, not one-to-one UI mappings
• Use @hidden directive to hide internal primary keys from Merged API clients
• Resolve schema conflicts through team collaboration and renaming/redefining types
• Use @canonical directive to designate authoritative data sources during conflicts
• Establish Schema architect or working group for cross-team coordination

Effective schema design for Merged APIs requires careful planning around team ownership, data relationships, and conflict resolution to create scalable, intuitive unified GraphQL interfaces.