Conditional resolving of fields

[pylipp]

Say I have

type Author {
  id: ID
  name: String
  books: [Book]
}
type Book {
  id: ID
  title: String
  author: Author
}
type Query {
  author(id: ID): Author
}

and a resolver implementation

query = QueryType()

@query.field("author")
def resolve(obj, info, id):
    data = orm.get_author(id).as_dict()
    data["books"] = orm.get_books_from_author(id).as_dict()
    return data

I would overfetch when doing a query like

query {
  author(id: "1") {
    name
  }
}

How can I work around this? Do I have access to the requested fields in the resolve function?

[rafalp]

How can I work around this?

Do you have a measurable data showing that this is degrading performance of your app?

You can look into requested fields from author resolver by looking up the contents of info instance, but overhead of python logic introspecting this object and mapping it to your ORM would be more than gains from limiting number of columns in your SQL query.

[pylipp]

Thank you for the quick reply!

How can I work around this?

Do you have a measurable data showing that this is degrading performance of your app?

I don't have data supporting that claim. It's something I assumed people are trying to avoid (don't query unnecessarily).

You can look into requested fields from author resolver by looking up the contents of info instance, but overhead of python logic introspecting this object and mapping it to your ORM would be more than gains from limiting number of columns in your SQL query.

Okay I see. It's good to know that the info introspection is costly. (Technically I think it's not the number of columns I'm trying to save but a complete second DB query call. First orm function above queries the authors table, second queries the books table)

[pylipp]

I think I was a bit confused here. I can write another resolver

author = ObjectType("Author")

@author.field("books")
def resolve_author_books(author_obj, info):
    return orm.get_books_from_author(author_obj.id)

The query resolver simplifies to

@query.field("author")
def resolve(obj, info, id):
    return orm.get_author(id)

and I can be sure that the books field will only be resolved when specified in the query body.