API for identifying selections from application context about lacinia

[stijnopheide]

We are using lacinia selections in a different way and not sure if that is as intended or whether this proposal will have any influence on that.

Our mutation resolvers for updating/creating content are very generic. On these resolvers we use [:com.walmartlabs.lacinia/selection :field-definition :args] and translate each argument into (a part of) a datomic transaction. We decorate our :input-objects with some information about the namespace of the datomic attribute and how relations should be constructed. If an input-object has a field that is not a scalar type, we'll look up the type in the schema and do this conversion recursively.

So, in short: we would need some way of identifying the type of the arguments being passed into the mutation resolver. On the other hand I think we could also do this by passing those types as a parameter of the resolver factory. So if the selection API is not public, we are going to change this before upgrading to 0.17.0.

[hlship]

We don't want to commit to freezing the format of the selection tree. For example, we're thinking about using more namespaced keywords for keys. And, over the course of the last couple of dot releases, we've added a couple of new keys to various schema definitions, and to the selection nodes.

I would say that the right way to do this is using field resolvers, which will have direct access to the arguments.

Again, back this up to your actual requirement: "We need the types of the argument values inside our field resolver." That's something that could be accomplished, either as meta data on the args map, or as an additional key in the supplied context.