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This GraphQL schema snippet causes an error:

medium📝 Debug Q7 of 15
GraphQL - Type Relationships
This GraphQL schema snippet causes an error:
type Post { id: ID! author: User } type User { id: ID! posts: [Post!]! }

What is the likely cause?
Aauthor field should be non-nullable (User!) to match posts list
Bposts field should be a single Post, not a list
CID fields must be strings, not ID type
DUser type is missing a required field
Step-by-Step Solution
Solution:
  1. Step 1: Check author field nullability

    Author is nullable (User), but posts list is non-nullable.
  2. Step 2: Match nullability for consistency

    Author should be non-nullable (User!) to ensure every Post has an author.
  3. Final Answer:

    author field should be non-nullable (User!) to match posts list -> Option A
  4. Quick Check:

    Nullability must be consistent in relationships [OK]
Quick Trick: Match nullability on both sides of relationship [OK]
Common Mistakes:
  • Ignoring nullability
  • Changing list to single object incorrectly
  • Misunderstanding ID type

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