Why should you care?

Mobile apps on slow networks avoid over-fetching REST payloads with nested includes.

See it live — copy this example

Paste into your MeanVerse project (Angular + Express + MongoDB), then run with ng serve / node / mongosh as noted.

import { ApolloServer } from '@apollo/server';
import { expressMiddleware } from '@as-integrations/express5';

const typeDefs = `
  type Account { id: ID! name: String! balance: Float! transfers(limit: Int): [Transfer!]! }
  type Query { account(id: ID!): Account }
`;

const resolvers = {
  Query: {
    account: (_: unknown, { id }: { id: string }, ctx: Context) =>
      ctx.accounts.load(id)
  },
  Account: {
    transfers: (parent, { limit = 5 }) => Transfer.find({ accountId: parent.id }).limit(limit)
  }
};

app.use('/graphql', expressMiddleware(server, { context: async ({ req }) => ({ user: req.user }) }));

What happened?

• Client sends query selecting nested fields.
• Resolvers fetch account then transfers — N+1 solved with DataLoader in ctx.accounts.load.

Practice next

1. Add Apollo Server alongside existing REST.
2. Define schema matching domain types.
3. Auth same JWT in GraphQL context.
4. Add mutation createTransfer with input type.
5. Persisted queries whitelist for mobile app.

Remember

GraphQL = client-shaped responses. Single endpoint; strong typing via schema. Coexist with REST during MeanVerse migration.

Mobile banking home

App needs greeting, balance, 3 transactions — one round trip.

Outcome: GraphQL query replaces three REST calls on 3G.