How can a many-to-many join table's attributes be exposed in a GraphQL-Ruby edge?

Question

I'm in the process of building a GraphQL API in a Rails 7 application, using the graphql-ruby gem.

In the app, users can create lists of catalogue items, and their lists can be manually ordered. So the simplified ActiveRecords look a bit like this:

class List < ApplicationRecord has_many :list_items has_many :items, through: :list_items end class ListItem < ApplicationRecord belongs_to :list belongs_to :item # attributes include :position, :updated_at, etc. end class Item < ApplicationRecord has_many :list_items has_many :lists, through: :list_items end

What I'd like to be able to do is to include the ListItem's attributes within the edge of the response, e.g.:

list(id: $id) { title createdAt items { edges { position updatedAt node { id title thumbnailUrl } } } }

I've tried creating custom Connection and Edge objects, but have so far failed to work out how to express that the edge has a direct ActiveRecord equivalence to a particular ListItem record such that I can retrieve the necessary attributes.

It is unclear what's your question. edges is just list_items? What is node? You said lists can be ordered manually, but in your query there is not any order attribute, what do you mean? — mechnicov
– mechnicov, Commented Mar 17, 2023 at 12:29
I find this very useful github.com/kashiftufail/graphql_api_nested — Muhammad Kashif Ali
– Muhammad Kashif Ali, Commented Jun 7, 2023 at 10:54

ScottM · Accepted Answer · 2023-03-17 11:22:10Z

So I think I've cracked it.

In my ListType I declare my custom connection:

module Types class ListType < Types::BaseObject field :id, ID, null: false field :title, String, null: false field :items, Types::ListItemConnectionType, connection: true def items object.list_items.order(:position) end end end

The connection inherits from my base connection type but specifies the custom edge type:

module Types class ListItemConnectionType < Types::BaseConnection edge_type Types::ListItemEdgeType end end

In the edge type, object.node is the ListItem record - so we need to provide a custom node method to expose its associated Item

module Types class ListItemEdgeType < Types::BaseEdge node_type(Types::ItemType) field :position, Integer field :updated_at, GraphQL::Types::ISO9601DateTime def position object.node.position end def updated_at object.node.updated_at end def node object.node.item end end end

If anybody has an alternative approach, I'd love to hear it.

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