Note, this repo follows up a companion video series on YouTube.

A demo chat GraphQL API built with apollo-server on top of Express.

apollo-server library exports a core class that you can instantiate with an options object.

new ApolloServer({
  typeDefs,
  resolvers,
  context,
  mocks,
  formatError,
  ...
})

In v1, typeDefs and resolvers were passed to makeExecutableSchema. The resulting schema would then be supplied to graphqlExpress middleware. In v2, ApolloServer only requires two arguments,

• typeDefs (Object) to declare the data types with SDL, and
• resolvers (Object) to resolve the schema with resolver functions

Some other optional arguments include

• context (Object) to share data across resolvers
• mocks (Boolean) to enable randomly-generated mocks
• formatError (Object or Function) to fine-tune the error format
• subscriptions (String or Object) to configure real-time updates
• schema (Object) for backwards compatibility with v1

To see a full list of arguments, refer to apollo-server API.

Previously, typeDefs were written in SDL using a template literal, which didn't allow for syntax highlighting. As of v2, typeDefs are invoked on gql with a tagged template, and can be color coded with an editor extension (such as GraphQL for VSCode).

const typeDefs = gql`
  type Query {
    user(id: ID!): User
  }
`

resolvers, unlike rootValue in express-graphql, allow for root-level and nested resolvers. Each resolver function falls under Query, Mutation, Subscription, or custom object type, and has the following signature

const resolvers = {
  Query: {
    user: (root, args, context, info) => { /*...*/ }
  }
}

This is different from rootValue resolvers in express-graphql

const rootValue = {
  user: (args, context, info) => { /*...*/ }
}

In apollo-server, root evaluates to either the parent field, or rootValue for top-level resolvers. See its value differs depending on the field. As with express-graphql, any fields that are not defined explicitly will be accessed as object props or invoked as methods on the root.