Support composite keys/inputs

[gmac]

It would add practical value if composite key selections were allowed. Composite keys would require an additional argument mapping to express how the composite selections map into query arguments:

input WidgetKey {
  group: String!
  name: String!
}

widgets(keys: [WidgetKey!]!, other: String): [Widget]! @stitch(
  key: "scope { group name }",
  arguments: "keys: {group: $scope.group, name: $scope.name}, other: 'Sfoo'"
)

The arguments param is parsed as a GraphQL inner-arguments literal. Then, paths from the key are inserted into the literal as a namespaced path prefixed by "$", ie: $scope.group. Some scoping rules would apply, as a repeatable key field can only be inserted into into a repeatable argument scope.

Arguments

type Widget {
  scope: String!
  name: String!
}

type Query {
  widget1(scope: String!, name: String!): Widget @stitch(
    key: "scope name",
    arguments: "scope: $scope, name: $name"
  )
  widget2(s: String!, n: String!): Widget @stitch(
    key: "scope name",
    arguments: "s: $scope, n: $name"
  )
}

Input objects

type Widget {
  scope: String!
  name: String!
}

input WidgetKey {
  scope: String!
  name: String!
}
input WidgetKey2 {
  s: String!
  n: String!
}
type Query {
  widgets(keys: [WidgetKey!]!): [Widget]! @stitch(
    key: "scope name", 
    arguments: "keys: {scope: $scope, name: $name}"
  )

  widget1(key: WidgetKey!): Widget @stitch(
    key: "scope name", 
    arguments: "key: {scope: $scope, name: $name}"
  )
  widget2(key: WidgetKey2!): Widget @stitch(
    key: "scope name", 
    arguments: "key: {s: $scope, n: $name}"
  )
  
  widget1(key: WidgetKey, other: String): Widget @stitch(
    key: "scope name", 
    arguments: "key: {scope: $scope, name: $name}, other: 'Sfoo'"
  )
  widget2(key: WidgetKey2, other: String): Widget @stitch(
    key: "scope name", 
    arguments: "key: {s: $scope, n: $name}, other: 'Sfoo'"
  )
}

Nested selections

type WidgetScope {
  group: String!
  name: String!
}
type Widget {
  scope: WidgetScope
  title: String
}

input WidgetKey {
  group: String!
  key: String!
}
type Query {
  widgets(keys: [WidgetKey!]!, other: String): [Widget]! @stitch(
    key: "scope { group name }",
    arguments: "keys: {group: $scope.group, name: $scope.name}, other: 'Sfoo'"
  )
}

Entity representations (Apollo Federation protocol)

type WidgetScope {
  group: String!
  name: String!
}
type Widget {
  scope: WidgetScope
  title: String
}

union _Entity = Widget
scalar _Any
type Query {
  # sends keys as JSON blobs:
  # [{"group": "a", name: "b", "__typename": "Widget"}, ...]
  _entities(representations: [_Any!]!): [_Entity]! @stitch(
    key: "scope { group name } __typename", 
    arguments: "representations: { group: $scope.group, name: $scope.name, __typename: $__typename }",
  )
}

Simple parser:

class ArgumentsParser
  class << self
    # "reps: {group: $scope.group, name: $scope.name}, other: 'Sfoo'""
    def parse(template)
      template = template.gsub("'", '"').gsub(/(\$[\w\.]+)/) { %|"#{_1}"| }
      GraphQL.parse("{ f(#{template}) }")
        .definitions.first
        .selections.first
        .arguments
    end
  end
end