Feature: add support for interface resolution (#21)

lib/federation.js

@@ -34,7 +34,9 @@ const {
  isTypeDefinitionNode,
  isTypeExtensionNode,
  isObjectType,
+ isInterfaceType,
  isSpecifiedDirective,
+ defaultTypeResolver,
  GraphQLDirective
 } = require('graphql')
 const { validateSDL } = require('graphql/validation/validate')
@@ -173,6 +175,35 @@ function addTypeNameToResult (result, typename) {
  return result
 }
 
+function resolveType (reference, context, info) {
+ const { __typename } = reference
+
+ const type = info.schema.getType(__typename)
+
+ if (!type || !(isObjectType(type) || isInterfaceType(type))) {
+ throw new MER_ERR_GQL_FEDERATION_INVALID_SCHEMA(__typename)
+ }
+
+ if (!isInterfaceType(type)) {
+ return type
+ }
+
+ const resolveTypeFn = type.resolveType || defaultTypeResolver
+
+ const resolveType = resolveTypeFn({
+ ...reference,
+ __typename: undefined
+ }, context, info, type)
+
+ if (typeof resolveType !== 'string' && typeof resolveType.then === 'function') {
+ return resolveType.then((resolvedTypename) =>
+ info.schema.getType(resolvedTypename)
+ )
+ }
+
+ return info.schema.getType(resolveType)
+}
+
 function addEntitiesResolver (schema) {
  const entityTypes = Object.values(schema.getTypeMap()).filter(
  type => isObjectType(type) && typeIncludesDirective(type, 'key')
@@ -199,12 +230,24 @@ function addEntitiesResolver (schema) {
  ...queryFields._entities,
  resolve: (_source, { representations }, context, info) => {
  return representations.map(reference => {
- const { __typename } = reference
+ const type = resolveType(reference, context, info)
+
+ if (type && typeof type.then === 'function') {
+ return type.then((resolvedType) => {
+ const resolveReference = resolvedType.resolveReference ||
+ function defaultResolveReference () {
+ return reference
+ }
+
+ const result = resolveReference(reference, {}, context, info)
 
- const type = info.schema.getType(__typename)
+ if (result && typeof result.then === 'function') {
+ return result.then((x) =>
+ addTypeNameToResult(x, resolvedType.name))
+ }
 
- if (!type || !isObjectType(type)) {
- throw new MER_ERR_GQL_FEDERATION_INVALID_SCHEMA(__typename)
+  return addTypeNameToResult(result, resolvedType.name)
+ })
  }
 
  const resolveReference = type.resolveReference
@@ -216,10 +259,11 @@ function addEntitiesResolver (schema) {
  const result = resolveReference(reference, {}, context, info)
 
  if (result && 'then' in result && typeof result.then === 'function') {
- return result.then(x => addTypeNameToResult(x, __typename))
+ return result.then((x) =>
+ addTypeNameToResult(x, type.name))
  }
 
- return addTypeNameToResult(result, __typename)
+ return addTypeNameToResult(result, type.name)
  })
  }
  }