Add queries/resolvers for single assets

resolvers.js

@@ -0,0 +1,21 @@
+function byCode(code) {
+  return item => item.code === code;
+}
+
+export default {
+  Country: {
+    continent: (country, args, {continents}) =>
+      continents.find(continent => continent.code === country.continent),
+    languages: (country, args, {languages}) =>
+      languages.filter(language => country.languages.includes(language.code))
+  },
+  Query: {
+    continent: (parent, args, {continents}) =>
+      continents.find(byCode(args.code)),
+    continents: (parent, args, {continents}) => continents,
+    country: (parent, args, {countries}) => countries.find(byCode(args.code)),
+    countries: (parent, args, {countries}) => countries,
+    language: (parent, args, {languages}) => languages.find(byCode(args.code)),
+    languages: (parent, args, {languages}) => languages
+  }
+};