index.ts

import { buildSchemaSync, Resolver, Query, ObjectType, Mutation, Field } from 'type-graphql'
import { ApolloServer } from 'apollo-server'
import 'reflect-metadata'

const plainUsersArray = [{
    id: 1,
    name: 'John Doe'
}, {
    id: 2,
    name: 'Foo'
}, {
    id: 3,
    name: 'Bar'
}]

@ObjectType()
class SimpleUser {
    @Field() id: number
    @Field() name: string
}

@ObjectType()
class Entity {
    @Field() id: number
}

@ObjectType()
class InheritedUser extends Entity {
    @Field() name: string
}

@Resolver()
class UserResolver {

    @Query(_ => [SimpleUser])
    users(): SimpleUser[] {
        return plainUsersArray
    }

    @Query(_ => [InheritedUser])
    inheritedUsers(): InheritedUser[] {
        return plainUsersArray
    }

    @Mutation(_ => String)
    someMutation() {
        return ""
    }
}

const schema = buildSchemaSync({ resolvers: [UserResolver] })
const apolloServer =  new ApolloServer({ schema })
apolloServer.listen(3000).then(() => {
    console.log('The server is listening...')
})

package.json

{
  "name": "type-graphql-test",
  "dependencies": {
    "apollo-server": "^2.1.0",
    "reflect-metadata": "^0.1.12",
    "ts-node": "^7.0.1",
    "type-graphql": "^0.14.0",
    "typescript": "^3.1.1"
  },
  "scripts": {
    "start": "ts-node index.ts"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "target": "es2018",
    "module": "commonjs",
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "lib": ["esnext"]
  },
  "include": ["index.ts"]
}