If an output object is not referenced as an output type it is not inserted into the schema

[grkek]

An example like this:

require "graphql"

@[GraphQL::Object]
class Wallet < GraphQL::BaseObject
  @[GraphQL::Field]
  property id : String

  def initialize(@id : String)
  end
end

@[GraphQL::Object]
class User < GraphQL::BaseObject
  @[GraphQL::Field]
  property wallets : Array(Wallet)

  def initialize(@wallets : Array(Wallet))
  end
end

@[GraphQL::Object]
class Query < GraphQL::BaseQuery
  @[GraphQL::Field]
  def list_users : Array(User)
    [User.new([Wallet.new("1"), Wallet.new("2")])] of User
  end
end

schema = GraphQL::Schema.new(Query.new)

puts schema.document.to_s

Will generate a schema document like this:

type Query {
  listUsers: [User!]!
}

"The `String` scalar type represents textual data, represented as UTF-8 character sequences. The String type is most often used by GraphQL to represent free-form human-readable text."
scalar String

type User {
  wallets: [Wallet!]!
}

type __Directive {
  args: [__InputValue!]!
  description: String
  locations: [String!]!
  name: String!
}

type __EnumValue {
  deprecationReason: String
  description: String
  isDeprecated: Boolean!
  name: String!
}

type __Field {
  args: [__InputValue!]!
  deprecationReason: String
  description: String
  isDeprecated: Boolean!
  name: String!
  type: __Type!
}

type __InputValue {
  defaultValue: String
  description: String
  name: String!
  type: __Type!
}

type __Schema {
  directives: [__Directive!]!
  mutationType: __Type
  queryType: __Type!
  subscriptionType: __Type
  types: [__Type!]!
}

type __Type {
  description: String
  enumValues(includeDeprecated: Boolean! = false): [__EnumValue!]
  fields(includeDeprecated: Boolean! = false): [__Field!]
  inputFields: [__InputValue!]
  interfaces: [__Type!]
  kind: __TypeKind!
  name: String
  ofType: __Type
  possibleTypes: [__Type!]
}

enum __TypeKind {
  ENUM
  INPUT_OBJECT
  INTERFACE
  LIST
  NON_NULL
  OBJECT
  SCALAR
  UNION
}

The Wallet class clearly has inherited from the object, but it is not serialised into the schema.