AppSync GraphQL Resolvers w/ Go in AWS Lambda

Easily create AWS AppSync resolvers with AWS Lambda using Go. See appsync-resolvers-example for an example project with custon Field and Query resolvers and how to set up, maintain, and deploy a working GraphQL API using the Serverless Application Model and without any third-party frameworks.

See Serverless GraphQL with AWS AppSync and Lambda on sbstjn.com for a detailed guide how to set up and configure this project. Or just run make configure build package deploy and you are ready to go …

Usage

Installation

$ > go get github.com/sbstjn/appsync-resolvers

Resolvers

import (
    "github.com/sbstjn/appsync-resolvers"
)

type personArguments struct {
    ID int `json:"id"`
}

func resolvePeople() (people, error) {
    return dataPeople, nil
}

func resolvePerson(p personArguments) (*person, error) {
    return dataPeople.byID(p.ID)
}

func resolveFriends(p person) (people, error) {
    return p.getFriends()
}

var (
    r = resolvers.New()
)

func init() {
    r.Add("query.people", resolvePeople)
    r.Add("query.person", resolvePerson)
    r.Add("field.person.friends", resolveFriends)
}

func main() {
    lambda.Start(r.Handle)
}

AppSync Configuration

Resolver lookup is based on a resolve property in your RequestMappingTemplate, which can be configured using the AWS Console or CloudFormation as well. This approach works fine with the recommended AWS setup for multiple custom resolvers and AWS Lambda data sources:

AppSyncDataSource:
  Type: AWS::AppSync::DataSource
  Properties:
    ApiId: !GetAtt [ AppSyncAPI, ApiId ]
    Name: resolver
    Type: AWS_LAMBDA
    LambdaConfig:
      LambdaFunctionArn: !GetAtt [ Lambda, Arn ]
    ServiceRoleArn: !GetAtt [ Role, Arn ]

AppSyncResolverPeople:
  Type: AWS::AppSync::Resolver
  Properties:
    ApiId: !GetAtt [ AppSyncAPI, ApiId ]
    TypeName: Query
    FieldName: people
    DataSourceName: !GetAtt [ AppSyncDataSource, Name ]
    RequestMappingTemplate: '{ "version" : "2017-02-28", "operation": "Invoke", "payload": { "resolve": "query.people", "context": $utils.toJson($context) } }'
    ResponseMappingTemplate: $util.toJson($context.result)

AppSyncResolverPerson:
  Type: AWS::AppSync::Resolver
  Properties:
    ApiId: !GetAtt [ AppSyncAPI, ApiId ]
    TypeName: Query
    FieldName: person
    DataSourceName: !GetAtt [ AppSyncDataSource, Name ]
    RequestMappingTemplate: '{ "version" : "2017-02-28", "operation": "Invoke", "payload": { "resolve": "query.person", "context": $utils.toJson($context) } }'
    ResponseMappingTemplate: $util.toJson($context.result)

AppSyncResolverFriends:
  Type: AWS::AppSync::Resolver
  Properties:
    ApiId: !GetAtt [ AppSyncAPI, ApiId ]
    TypeName: Person
    FieldName: friends
    DataSourceName: !GetAtt [ AppSyncDataSource, Name ]
    RequestMappingTemplate: '{ "version" : "2017-02-28", "operation": "Invoke", "payload": { "resolve": "field.person.friends", "context": $utils.toJson($context) } }'
    ResponseMappingTemplate: $util.toJson($context.result)

Head over to appsync-resolvers-example for an example project and how simple it can be to set up, maintain, and deploy a serverless GraphQL API with AWS AppSync using the Serverless Application Model.

License

Feel free to use the code, it's released using the MIT license.

Contribution

You are welcome to contribute to this project! 😘

To make sure you have a pleasant experience, please read the code of conduct. It outlines core values and beliefs and will make working together a happier experience.