How to filter out entire query based on a nested field filter with different data source

[alrz]

Consider some query type as follows:

type Query {
   orders: [OrderQuery]
}

type OrderQuery {
  order: Order # efcore
  details: [OrderDetail] # mongo
}
# or
type OrderQuery {
  order: Order # efcore
  detail: OrderDetail # mongo
}

The scenario is similar to https://elixirforum.com/t/multiple-filters-for-related-object-types-with-a-graphql-absinthe-dataloader/29896. We want to define filters for both order and detail(s) which are fetched from different data sources.

Now if the filters on detail(s) returns nothing we want to skip that record entirely, this is like an inner join applied after both data loaders are run in a stacked manner: we first get orders and try to fetch relevant details with those keys afterwards.

As mentioned in the link above, the join must be done on the app layer. My question is how that could be done in an efficient manner?

Thanks.