Apollo Server模式拼接使用mergeSchemas，如何从单独的模式中使用类型？

// userSchema.js

import { gql } from 'apollo-server';

const userSchema = gql`
  type User {
    id: ID!
    name: String!
    email: String!
  }

  type Query {
    getUser(id: ID!): User
  }
`;

export default userSchema;

// postSchema.js

import { gql } from 'apollo-server';

const postSchema = gql`
  type Post {
    id: ID!
    title: String!
    content: String!
  }

  type Query {
    getPost(id: ID!): Post
  }
`;

export default postSchema;

// index.js

import { ApolloServer } from 'apollo-server';
import { mergeSchemas } from 'graphql-tools';
import userSchema from './userSchema';
import postSchema from './postSchema';

const schema = mergeSchemas({
  schemas: [userSchema, postSchema],
});

const server = new ApolloServer({ schema });

server.listen().then(({ url }) => {
  console.log(`Server ready at ${url}`);
});