How to get correct type for federation field that requires on an external list field

[Rtwena]

Using the plugin @pothos/plugin-federation

Given the graphql schema

type Cart
  @key(fields: "id")
  @extends
{
  lineItemsStock: [LineItemStock!]! @external
  id: ID!
  canCheckout: Boolean! @requires(fields: "lineItemsStock { stock sku }")
}

canCheckout is a field that requires lineItemsStock { stock sku }. lineItemsStock is a list.

When writing the pothos builder that generates the above schema

export const CartRef = builder.externalRef<Selection<{ id: string }>, Cart>('Cart', builder.selection('id')).implement({
  externalFields: (fieldBuilder) => ({
    lineItemsStock: fieldBuilder.field({
      type: [LineItemStockRef],
    }),
  }),
  fields: (fieldBuilder) => ({
    id: fieldBuilder.exposeID('id'),
    canCheckout: fieldBuilder.boolean({
      requires: builder.selection<{ lineItemsStock: LineItemStock }>('lineItemsStock { stock sku }'),
      // types for requires on a list field are incorrect
      resolve: (cart) => canCheckout(cart as unknown as Cart & { lineItemsStock: LineItemStock[] }),
    }),
  }),
})

the builder.selection doesn't like if LineItemStock is an array like LineItemStock[], it appears to create a circular type. This means that the resolve function that passes cart has the type incorrect for cart, since it thinks lineItemsStock is not a list.

The correct type for cart would be Cart & { lineItemsStock: LineItemStock[] }. But i'm unsure where I can tell the builder that it should be that.

[hayes]

You are providing the type in your requires section, so it should be:

export const CartRef = builder.externalRef<Selection<{ id: string }>, Cart>('Cart', builder.selection('id')).implement({
  externalFields: (fieldBuilder) => ({
    lineItemsStock: fieldBuilder.field({
      type: [LineItemStockRef],
    }),
  }),
  fields: (fieldBuilder) => ({
    id: fieldBuilder.exposeID('id'),
    canCheckout: fieldBuilder.boolean({
      requires: builder.selection<{ lineItemsStock: LineItemStock[] }>('lineItemsStock { stock sku }'),
      resolve: (cart) => canCheckout(cart),
    }),
  }),
})

[hayes]

sorry, misread your original message. This might need to be updated in the selection helper, let me look into that

[hayes]

I just kicked off a release with a fix for this. It should work correctly after upgrading. Let me know if you have any other issues

[Rtwena]

Wow perfect, thanks for the quick fix!