methods do not know what info to provide

[MARTIMM]

Users can ask things via a query but can also leave out items they do not need in the query. The methods, on the other hand, do not know what is left out from the query and must provide all data. This could involve expensive calculations or database lookups.

[CurtTilmes]

Each method can just provide the information it is asked for. If something is expensive to calculate or look up, just don't do it until explicitly asked for that item.

For example, if you have an "Item" with method foo and bar which are expensive:

class Item
{
    method foo(--> Str) {...}
    method bar(--> Str) {...}
}
class Query
{
    method item(--> Item) { Item.new }
}

my $schema = GraphQL::Schema.new(Item, Query);

with a query like this:

{
    item { foo }
}

It will call Item.foo, but won't call Item.bar.

[MARTIMM]

Hi Curt,
Thanks for your answer. I just misunderstood an example from the docs where you showed an example of a User class with only some attributes. The object from this class was filled in by some other method and returned the object. It was a mistake of mine not to think a bit further about how the attribute is handled by perl6. E.g.

class User {
  has $.id is rw;
...
}

is something like

class User {
  has $!id;
  method id( ) is rw { ...; $!id; }
}

which provides for reading as well as writing.

Regards,
Marcel

[MARTIMM]

btw;
How does a method know that it was used for reading(query {...}) or for writing (mutation {...})? Do I need to specify different methods?

[CurtTilmes]

It is really up to you to organize things that way. If you do a mutation type activity within a query method, nothing will stop you.

I've just been making a 'top-level' class Query {} with all my queries and class Mutation {} with all my mutations. That fits with the conventions, works well with GraphiQL and makes it very clear.

[MARTIMM]

ah, another overlooked thing. I knew that it was possible to do modifications in a query but that it wasn't recommended. Studying your code I see that the schema must be set using :query and/or :mutation named attributes, of which you told me about the first one before. It might be an idea to have a pod document for at least the GraphQL.pm6 module.

Anyway, thanks for your help,
Marcel