Union type for prisma nodes

[P4sca1]

How do you create a union type which consists of object types created with t.prismaNode?

[P4sca1]

I tried using the return types of t.prismaNode in the types array, which yields the correct schema, but throws a runtime error, that I need to either define resolveType on the union or isTypeOf on the node.
Is this something, that can be solved using the branding that pothos adds to prisma objects?

[P4sca1]

I found out how to do it 🥳
You need to add typeBrandKey when returning the nodes, so that Pothos / GraphQL knows the correct type of the object at runtime.

import { typeBrandKey } from '@pothos/core'

const NodeA = builder.prismaNode({ ... })
const NodeB = builder.prismaNode({ ... })

const MyUnion = builder.unionType('MyUnion', { types: [NodeA, NodeB] })

builder.queryFields((t) => ({
  myUnionQuery: t.field({
    type: MyUnion,
    resolve: () => {
      // ...
      return {
        ...prismaNode,
        [typeBrandKey]: 'NodeA' // The name of the prisma model that is returned
      }
    }
})

[hayes]

this works, typeBrandKey is an internal symbol pothos uses when loading relay nodes. The normal way to do this is to add a __typename, this is what graphql uses by default, pothos uses [typeBrandKey] because it won't be as likely to interfere with existing properties. I've seen __typename added to the DB as a column with a default value, which avoids needing to add it manually.

NodeA.addBrand(result) will accept either a single item or an array, and will add the branded property as a non-enumerable property. This is how pothos does it internally.

[hayes]

relevant prisma issue: prisma/prisma#5315

[P4sca1]

Thanks for the hint on the addBrand(result) helper method.