serverless-appsync-plugin codegen

appsync-mt-gen.js

// creates a `mapping-templates` folder with the velocity templates
// for each query and mutation defined in your schema.graphql
// and a `sls-appsync-mt.yml` to use inside of `serverless.yml`:
// custom.appsync.mappingTemplates: ${file(./sls-appsync-mt.yml)}

import fs, { readFileSync } from 'fs'
import { join } from 'path'

import { introspectSchema } from 'apollo-codegen'
import ejs from 'ejs'
import yaml from 'node-yaml'

const generateVelocityTemplate = ({ type = 'request', field }) => {
  try {
    const template = fs.readFileSync(join(__dirname, `../scripts/${type}-mapping-template.tmpl.ejs`), 'utf-8')
    const mtContents = ejs.render( template, field ? { field } : {} )
    const outPath = `./mapping-templates/${field ? `${field}-` : ''}${type}-mapping-template.txt`
    fs.writeFileSync(outPath, mtContents, 'utf-8')
  } catch (err) {
    console.log(err)
  }
}

introspectSchema(
  join(__dirname, '../schema.graphql'),
  join(__dirname, './schema.json')
)
  .then(() => {
    const schema = require('./schema.json').data.__schema

    const toResolve = schema.types.reduce((toResolve, y) => {
      if(
        y.name === schema.queryType.name || 
        y.name === schema.mutationType.name
      ) {
        toResolve = [
          ...toResolve,
          ...y.fields.map(f => ({
            field: f.name,
            type: y.name === schema.queryType.name ? 'Query' : 'Mutation',
          }))
        ]
      }
      return toResolve
    }, [])
  
    const slsConf = []
    let dataSource = process.argv.length > 2 ? process.argv[2] : null
    dataSource = dataSource || 'Lambda'

    const dir = './mapping-templates'
    if (!fs.existsSync(dir)) {
      fs.mkdirSync(dir)
    }

    toResolve.map((data) => {
      const { field } = data
      slsConf.push({
        dataSource,
        ...data,
        request: `${field}-request-mapping-template.txt`,
        response: 'response-mapping-template.txt',
      })
      generateVelocityTemplate({ field })
    })
    generateVelocityTemplate({ type: 'response' })

    yaml.writeSync(join(__dirname, '../sls-appsync-mt.yml'), slsConf)
    fs.unlinkSync(join(__dirname, './schema.json'))
  })
  .catch(err => console.error(err))

Comment.graphql

type Comment {
	_id: String!
	# The comment's content.
	content: String!
	# The comment timestamp. This field is indexed to enable sorted pagination.
	createdAt: String!
}

type Mutation {
	# Comment on an event.
	commentOnEvent(eventId: ID!, content: String!, createdAt: String!): Comment
}

type Subscription {
	subscribeToEventComments(eventId: String!): Comment
		@aws_subscribe(mutations: ["commentOnEvent"])
}

Event.js

type Event {
	_id: ID!
	name: String!
	where: String!
	when: String!
	description: String
	# Paginate through all comments belonging to an individual post.
	comments: [Comment]
}

type Query {
	# Get a single event by id.
	getEvent(_id: ID!): Event
	# Paginate through events.
	listEvents(limit: Int = 10): [Event]
}

type Mutation {
	# Create a single event.
	createEvent(
		name: String!,
		when: String!,
		where: String!,
		description: String
	): Event
	# Delete a single event by id.
	deleteEvent(_id: ID!): Event
}

type Subscription {
	subscribeToNewEvent: Event
		@aws_subscribe(mutations: ["createEvent"])
}

request-mapping-template.tmpl.ejs

{
  "version": "2017-02-28",
  "operation": "Invoke",
  "payload": {
      "field": "<%= field %>",
      "arguments":  $utils.toJson($context.arguments)
  }
}

response-mapping-template.tmpl.ejs

$util.toJson($context.result)

root.graphql

schema {
	query: Query
	mutation: Mutation
	subscription: Subscription
}

schema-merge.js

// merges all the sub-schemas into `schema.graphql`

import path from 'path'
import fs from 'fs'
import { fileLoader, mergeTypes } from 'merge-graphql-schemas'

const typesArray = fileLoader(path.join(__dirname, '../schema'))
const schema = mergeTypes(typesArray, { all: true })

fs.writeFile(path.join(__dirname, '../schema.graphql'), `# AUTOGENERATED\n${schema.toString()}`, function(err) {
  if(err) {
    return console.log(err)
  }
}) 

schema.graphql

# AUTOGENERATED
schema {
  query: Query
  mutation: Mutation
  subscription: Subscription
}

type Query {
  # Get a single event by id.
  getEvent(_id: ID!): Event
  # Paginate through events.
  listEvents(limit: Int = 10): [Event]
}

type Mutation {
  # Comment on an event.
  commentOnEvent(eventId: ID!, content: String!, createdAt: String!): Comment
  # Create a single event.
  createEvent(name: String!, when: String!, where: String!, description: String): Event
  # Delete a single event by id.
  deleteEvent(_id: ID!): Event
}

type Subscription {
  subscribeToEventComments(eventId: String!): Comment @aws_subscribe(mutations: ["commentOnEvent"])
  subscribeToNewEvent: Event @aws_subscribe(mutations: ["createEvent"])
}

type Comment {
  _id: String!
  # The comment's content.
  content: String!
  # The comment timestamp. This field is indexed to enable sorted pagination.
  createdAt: String!
}

type Event {
  _id: ID!
  name: String!
  where: String!
  when: String!
  description: String
  # Paginate through all comments belonging to an individual post.
  comments: [Comment]
}

sls-appsync-mt.yml

# AUTOGENERATED
- dataSource: Lambda
  field: getEvent
  type: Query
  request: getEvent-request-mapping-template.txt
  response: response-mapping-template.txt
- dataSource: Lambda
  field: listEvents
  type: Query
  request: listEvents-request-mapping-template.txt
  response: response-mapping-template.txt
- dataSource: Lambda
  field: commentOnEvent
  type: Mutation
  request: commentOnEvent-request-mapping-template.txt
  response: response-mapping-template.txt
- dataSource: Lambda
  field: createEvent
  type: Mutation
  request: createEvent-request-mapping-template.txt
  response: response-mapping-template.txt
- dataSource: Lambda
  field: deleteEvent
  type: Mutation
  request: deleteEvent-request-mapping-template.txt
  response: response-mapping-template.txt

folder structure

• scripts/
  • appsync-mt-gen-js
  • request-mapping-template.tmpl.ejs
  • response-mapping-template.tmpl.ejs
  • schema-merge.js
• schema/
  • Comment.js
  • Event.js
  • root.js
• schema.graphql
• sls-appsync-mt.yml