Resolvers

Resolver adalah fungsi yang menyediakan data untuk setiap field di schema. Saat client query sebuah field, resolver yang sesuai dipanggil.

Anatomy of a Resolver

// resolver(parent, args, context, info)
const resolvers = {
  Query: {
    user: async (parent, { id }, context) => {
      return context.db.users.findById(id);
    },
    users: async (parent, { limit, offset }, context) => {
      return context.db.users.findMany({ take: limit, skip: offset });
    },
  },

  Mutation: {
    createUser: async (parent, { input }, context) => {
      return context.db.users.create({ data: input });
    },
  },

  // Field-level resolver
  User: {
    posts: async (parent, args, context) => {
      // parent = user object dari parent resolver
      return context.db.posts.findMany({
        where: { authorId: parent.id },
      });
    },
    fullName: (parent) => {
      return `${parent.firstName} ${parent.lastName}`;
    },
  },
};

Resolver Arguments

• parent — Result dari parent resolver (root = undefined)
• args — Arguments yang dikirim di query
• context — Shared per-request (db connection, auth user, loaders)
• info — AST info tentang query (advanced, jarang dipakai)

Context Setup

// Server setup (Apollo Server)
const server = new ApolloServer({
  typeDefs,
  resolvers,
});

// Context per request
const { url } = await startStandaloneServer(server, {
  context: async ({ req }) => ({
    db: prisma,
    user: await getAuthUser(req.headers.authorization),
    loaders: createLoaders(), // DataLoader instances
  }),
});

Default Resolvers

// GraphQL punya default resolver: parent[fieldName]
// Jadi jika parent.name sudah ada, tidak perlu resolver untuk field "name"

// Hanya tulis resolver jika:
// 1. Field butuh custom logic (computed field)
// 2. Field butuh data dari sumber lain (database query)
// 3. Field butuh transformasi