What must be the result of executing only one fragment on a list of union or interface type?

[xperiandri]

Having types Fruit and Vegetable implementing Produce as per https://graphql.com/learn/interfaces-and-unions/#fragments After I executed such query (use no shared fields, and only a sible type fragment while the collecton has multiple types)

query GetMostPopularStallProduce {
  mostPopularStall {
    availableProduce {
      ...  on Fruit {
        hasEdibleSeeds
      }
    }
  }
}

I've got

{
  "data": {
    "mostPopularStall": {
      "availableProduce": [
        {
          "hasEdibleSeeds": false
        },
        {
          "hasEdibleSeeds": true
        },
        {
          "hasEdibleSeeds": false
        },
        {},
        {}
      ]
    }
  }
}

Is it the correct behavior?

Specification does not mention such case at all.

I want to understand both cases like:

1. Nullable items

   type Stall {
   availableProduce: [Produce]
   }

2. Not tullable items

   type Stall {
   availableProduce: [Produce!]
   }

In context of fixing https://github.com/fsprojects/FSharp.Data.GraphQL/issues/455 in https://github.com/fsprojects/FSharp.Data.GraphQL/pull/458

[benjie]

Is it the correct behavior?

Yes. The relevant flow is:

• [ExecuteField()](https://spec.graphql.org/draft/#ExecuteField()) on availableProduce
• [CompleteValue()](https://spec.graphql.org/draft/#CompleteValue()) on a list type
• [CompleteValue()](https://spec.graphql.org/draft/#CompleteValue()) on each item
  • [ResolveAbstractType()](https://spec.graphql.org/draft/#ResolveAbstractType()) for each item
  • [ExecuteSelectionSet()](https://spec.graphql.org/draft/#ExecuteSelectionSet()) for this concrete type for each item
  • [CollectFields()](https://spec.graphql.org/draft/#CollectFields()) for this type for this selection set
  • selection is InlineFragment
  • [DoesFragmentTypeApply()](https://spec.graphql.org/draft/#DoesFragmentTypeApply()) returns either true or false
  • If false, no more selections -> empty object
  • If true, process additional selections

[JoviDeCroock]

I guess currently it's a bit implicit in the sense that we say Initialize resultMap to an empty ordered map. and then we see that the fragment does not apply so it stays an empty ordered map. I think there might be an opportunity to clarify something along the lines of If a returned object has no matching fragments the result will be an empty ordered map..

[benjie]

I think adding an example that demonstrates this might be helpful; the algorithm itself seems unambiguous.