Type inheritance: How to inherit a set of fields derived from variable field name

[nimmolo]

In Rails, I have a bunch of models that have an associated thumb_image_id --- only it's not always called that in the db - sometimes it's image_id, and for the Image model it's just id.

But generally, the client doesn't have much use for the image_id. It wants the urls... and in the front end, many urls are often required for a single responsive image. So I have a helper method, Image.url(:size, :image_id) that can generate the correct url for the specified size image, from animage_id. The sizes can be :thumbnail, :small, :medium, :large, :huge, :full.

In GraphQL, I'd like the Type objects for those models to be able to return :img_url_{size} fields for each of the responsive image sizes, using the helper to derive the urls from the id in the proper db column, without redefining the 6 derived fields in every Type.

I am imagining those model Types inheriting from a BaseWithImage type. Only certain Type objects should get these fields, so they're not added to Types::BaseObject:

module Types::Models
  class User < Types::Models::BaseWithImage
    field :id, Integer, null: false
    field :image_id, Integer, null: true
    ...
    # somehow tell Types::Models::BaseWithImage that the @image_field_name is "image_id" in this Type
    # maybe @image_field_name = "image_id"

module Types::Models
  class Herbarium < Types::Models::BaseWithImage
    field :id, Integer, null: false
    field :thumb_image_id, Integer, null: true
    ...
    # somehow tell Types::Models::BaseWithImage that the @image_field_name is "thumb_image_id" in this Type        
    # maybe @image_field_name = "thumb_image_id"

module Types::Models
  class BaseWithImage < Types::BaseObject
    field :img_src_thumb, String, null: true do
      Image.url(:thumbnail, object.send(@image_field_name.to_sym))
    end
    field :img_src_sm, String, null: true do
      Image.url(:small, object.send(@image_field_name.to_sym))
    end
    field :img_src_med, String, null: true do
      Image.url(:medium, object.send(@image_field_name.to_sym))
    end
    field :img_src_lg, String, null: true do
      Image.url(:large, object.send(@image_field_name.to_sym))
    end
    field :img_src_huge, String, null: true do
      Image.url(:huge, object.send(@image_field_name.to_sym))
    end
    field :img_src_full, String, null: true do
      Image.url(:full, object.send(@image_field_name.to_sym))
    end

and then somehow (this code does not work! plus I'm realizing Functions are deprecated, this is just for illustration)

class Functions::ImageUrlFunction < GraphQL::Function
  attr_accessor :size, :image_field_name  

  description "Retrieve image URL by size and image_field_name"

  def initialize(image_field_name, size)
    @size = size
    @image_field_name = image_field_name
  end

  def call(_obj, _args, _ctx)
    Image.url(@size.to_sym, object.send(@image_field_name.to_sym))
  end

that would resolve the call to Image.url(:size, :id) using the :size passed from BaseWithImage, and the name of the field that accesses the id ("image_id"or "thumb_image_id") passed from Types::Models::User etc.

My problem is I don't understand how to pass the name of the field up to that GraphQL::Function through the BaseWithImageclass I'm inheriting from. Can I set an instance variable in Types::Models::User @image_field_name = "image_id" and send it to my function from Types::Models::BaseWithImage? Or is this not the GraphQL way to do it?

[nimmolo]

Ah! Of course, it's an Interface i want. So much easier than i thought!

module Types::Models
  class UserType < Types::BaseObject
    implements Types::ImageUrls

module Types::ImageUrls
  include Types::BaseInterface
  description "Fields generating urls from image_id, thumb_image_id, etc"

  field :img_src_thumb, String, null: true
  field :img_src_sm, String, null: true
  field :img_src_med, String, null: true
  field :img_src_lg, String, null: true
  field :img_src_huge, String, null: true
  field :img_src_full, String, null: true

  def db_image_id
    case object
    when ::User
      object.image_id
    when ::Image
      object.id
    when ::Observation, ::GlossaryTerm
      object.thumb_image_id
    else
      raise("Unexpected Object: #{object.inspect}")
    end
  end

  def img_src_thumb
    Image.url(:thumbnail, db_image_id)
  end

  def img_src_sm
    Image.url(:small, db_image_id)
  end

  def img_src_med
    Image.url(:medium, db_image_id)
  end

  def img_src_lg
    Image.url(:large, db_image_id)
  end

  def img_src_huge
    Image.url(:huge, db_image_id)
  end

  def img_src_full
    Image.url(:full_size, db_image_id)
  end

  # Optional, see below
  definition_methods do
    # Optional: if this method is defined, it overrides `Schema.resolve_type`
    def resolve_type(object, context)
      # ...
    end
  end
end