docs: document upserts which "do nothing" to return row

Right now when you use an upsert mutation and there is a conflict, you’re unable to return the row. For example:

mutation update_participants {
  insert_participants(objects: {user_id: "1"}, on_conflict: {constraint: participants_user_id_sprint_token_key, update_columns: []}) {
    returning {
      id
      user_id
    }
  }
}

Will return:

{
  "data": {
    "insert_participants": {
      "returning": []
    }
  }
}

Instead, what it should return:

{
  "data": {
    "insert_participants": {
      "returning": [{
        id: 1,
        user_id: 1
      }]
    }
  }
}

Right now if you want to mimic this behavior you need to run a query to see if a record exists followed by a mutation to create if it doesn’t.

[0x777]

@timminkov Unfortunately empty update_columns translates to Postgres’s on conflict do nothing and that doesn’t return any results. So a simple work around is to update one of the columns from the unique constraint (update_columns: [user_id]).

[colemerrick]

@timminkov Unfortunately empty update_columns translates to Postgres’s on conflict do nothing and that doesn’t return any results. So a simple work around is to update one of the columns from the unique constraint (update_columns: [user_id]).

This forces you to set some bizarre permissions on a db level ie the least dangerous column to update in your unique constraint. Therefore, we really need a real upsert mutation - not an insert on conflict: https://hasura.io/docs/latest/graphql/core/databases/postgres/mutations/upsert.html.