graphql-design

GraphQL Design

Schema Design

type Query {
  user(id: ID!): User
  users(filter: UserFilter, first: Int = 20, after: String): UserConnection!
}

type Mutation {
  createUser(input: CreateUserInput!): CreateUserPayload!
  updateUser(id: ID!, input: UpdateUserInput!): UpdateUserPayload!
}

type Subscription {
  orderStatusChanged(orderId: ID!): Order!
}

type User {
  id: ID!
  email: String!
  name: String!
  orders(first: Int = 10, after: String): OrderConnection!
  createdAt: DateTime!
}

input CreateUserInput {
  email: String!
  name: String!
}

type CreateUserPayload {
  user: User
  errors: [UserError!]!
}

type UserError {
  field: String!
  message: String!
}

type UserConnection {
  edges: [UserEdge!]!
  pageInfo: PageInfo!
  totalCount: Int!
}

type UserEdge {
  node: User!
  cursor: String!
}

type PageInfo {
  hasNextPage: Boolean!
  endCursor: String
}

Use Relay-style connections for pagination. Return payload types from mutations with both result and errors.

Resolvers

const resolvers: Resolvers = {
  Query: {
    user: async (_, { id }, ctx) => {
      return ctx.dataloaders.user.load(id);
    },
    users: async (_, { filter, first, after }, ctx) => {
      const cursor = after ? decodeCursor(after) : undefined;
      const users = await ctx.db.user.findMany({
        where: buildFilter(filter),
        take: first + 1,
        cursor: cursor ? { id: cursor } : undefined,
        orderBy: { createdAt: "desc" },
      });

      const hasNextPage = users.length > first;
      const edges = users.slice(0, first).map(user => ({
        node: user,
        cursor: encodeCursor(user.id),
      }));

      return {
        edges,
        pageInfo: {
          hasNextPage,
          endCursor: edges[edges.length - 1]?.cursor ?? null,
        },
      };
    },
  },

  Mutation: {
    createUser: async (_, { input }, ctx) => {
      const existing = await ctx.db.user.findUnique({ where: { email: input.email } });
      if (existing) {
        return { user: null, errors: [{ field: "email", message: "Already taken" }] };
      }
      const user = await ctx.db.user.create({ data: input });
      return { user, errors: [] };
    },
  },

  User: {
    orders: async (parent, { first, after }, ctx) => {
      return ctx.dataloaders.userOrders.load({ userId: parent.id, first, after });
    },
  },
};