Arbitrary return value on field/connection

Usually, resolver simply returns a single object or scalar value that comply with defined types.

However, the resolver can bypass type definition with type coercion and can return any arbitrary value regardless of the client's query definition.

• e.g. marking the field as required in client Query, but returning undefined despite the query requiring the field.

// example using sql
getAuthor(_, args){
  return sql.raw('SELECT * FROM authors WHERE id = %s', args.id);
}
// example calling api endpoint
posts(author){
  return request(`https://api.blog.io/by_author/${author.id}`);
}

// returning undefined
names(author){
  return undefined;
}

Meaning, you can create any arbitrary connection between any query/node with another query/node.

• Each node's connection in graph (defined by resolver) is an independent connection.
  • Because resolver/connection is defined on each individual node's field level, seemingly identical connection will yield different results
    • e.g. Query > User > Name connection may have different data than Query > Group > User > Name
  • Because resolvers return some arbitrary return value, it may even return results that doesn't make logical sense
    • e.g. User.name may yield 123-213-4545 even though it's clearly a phone number if the resolver defines it that way.

User {
  Address {
    City
  }
  Age
  Name
}

User, Address, Age, and Name are all individual nodes connected by resolver field definitions.

null or undefined return value

Indicates that the value for the field could not be found.

If your schema indicates that this resolver's field is nullable, then the operation result has a null value at the field's position.

If this resolver's field is not nullable, Apollo Server sets the field's parent to null.

If necessary, this process continues up the resolver chain until it reaches a field that is nullable.

This ensures that a response never includes a null value for a non-nullable field. When this happens, the response's errors property will be populated with relevant errors concerning the nullability of that field.