How do I specify polymorphic types with graphql-ruby?

Question

I have a UserType and a userable that can be a Writer or Account.

For GraphQL I figured maybe I could use a UserableUnion like this:

UserableUnion = GraphQL::UnionType.define do name "Userable" description "Account or Writer object" possible_types [WriterType, AccountType] end

and then define my UserType like this:

UserType = GraphQL::ObjectType.define do name "User" description "A user object" field :id, !types.ID field :userable, UserableUnion end

But I get schema contains Interfaces or Unions, so you must define a 'resolve_type (obj, ctx) -> { ... }' function

I have tried putting a resolve_type in multiple places, but I can't seem to figure this out?

Does any one now how to implement this?

Marc Greenstock · Accepted Answer · 2016-11-11 21:43:04Z

That error means you need to define the resolve_type method in your app schema. It should accept an ActiveRecord model and the context, and return a GraphQL type.

AppSchema = GraphQL::Schema.define do resolve_type ->(record, ctx) do # figure out the GraphQL type from the record (activerecord) end end

You could either implement this example which links a model to a type. Or you could create a class method or attribute on your models that refer to their types. e.g.

class ApplicationRecord < ActiveRecord::Base class << self attr_accessor :graph_ql_type end end class Writer < ApplicationRecord self.graph_ql_type = WriterType end AppSchema = GraphQL::Schema.define do resolve_type ->(record, ctx) { record.class.graph_ql_type } end

BlueConga · Accepted Answer · 2021-02-01 11:13:35Z

Now there is UnionType in GraphQL Ruby

https://graphql-ruby.org/type_definitions/unions.html#defining-union-types

It has clear example how define UnionType that you can use.

class Types::CommentSubject < Types::BaseUnion description "Objects which may be commented on" possible_types Types::Post, Types::Image # Optional: if this method is defined, it will override `Schema.resolve_type` def self.resolve_type(object, context) if object.is_a?(BlogPost) Types::Post else Types::Image end end end

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