RFC(graphcache): Configurable Cache Directives

[kitten]

Summary

We have three categories of features and problems that have come up repeatedly and have a potentially common solution:

• When using relayPagination/simplePagination/custom resolvers that merge fields, it's impossible to tell when these resolvers should actually be not used
  • if a paginated field is used for infinite pagination and regular pagination, and both happen in the same query, they conflict.
  • if a paginated field shouldn't be infinitely paginated in another query, a custom wrapper must be written around the helpers to prevent this manually
• We have considered the addition of @required and @optional directives, which “preempt” the support for nullability operators on the client-side, and are an alternative to schema awareness
  • They further become more important when we consider future scenarios where fragments may be partially loading, while the full query has only partially resolved against the cache
• We have past requests for being able to selectively apply resolvers or not: RFC: Allow for selectively skipping local resolver with a hook option #2650

We could consider solving these problems in one go by adding custom directive support to Graphcache. With custom directives, instead of adding additional “switching/toggling” logic to Graphcache, we make potentially arbitrary resolvers configurable.

e.g. relayPagination could be included as an @relayPagination directive.

Proposed Solution

cacheExchange({
  directives: {
    relayPagination,
    required,
    optional,
    asDate: (parent, args, cache, info) {
      return new Date(cache.resolve(parent, info.parentFieldKey));
    },
  },
});

Some questions that require further consdieration (TBD):

• Will directives simply ever be resolvers?
• Will they have the same shape and should there be a shortcut for cache.resolve(parent, info.parentFieldKey)?
• How does this affect typing and is @required and @optional feasibly implemented as a resolver?
• How do we deal with directives on fragments?

Requirements

TBD