AWS AppSync JavaScript resolver context object reference

AWS AppSync defines a set of variables and functions for working with request and response handlers. This makes logical operations on data easier with GraphQL. This document describes those functions and provides examples.

Accessing the `context`

The context argument of a request and response handler is an object that holds all of the contextual information for your resolver invocation. It has the following structure:


type Context = {
  arguments: any;
  args: any;
  identity: Identity;
  source: any;
  error?: {
    message: string;
    type: string;
  };
  stash: any;
  result: any;
  prev: any;
  request: Request;
  info: Info;
};

Note

You will often find that the context object is referred to as ctx.

Each field in the context object is defined as follows:

`context` fields

arguments

A map that contains all GraphQL arguments for this field.

identity

An object that contains information about the caller. For more information about the structure of this field, see Identity.

source

A map that contains the resolution of the parent field.

stash

The stash is an object that is made available inside each resolver and function handler. The same stash object lives through a single resolver run. This means that you can use the stash to pass arbitrary data across request and response handlers and across functions in a pipeline resolver.

Note

You cannot delete or replace the entire stash, but you can add, update, delete, and read properties of the stash.

You can add items to the stash by modifying one of the code examples below:


//Example 1
ctx.stash.newItem = { key: "something" }

//Example 2
Object.assign(ctx.stash, {key1: value1, key2: value})

You can remove items from the stash by modifying the code below:


delete ctx.stash.key

result

A container for the results of this resolver. This field is available only to response handlers.

For example, if you're resolving the author field of the following query:


query {
    getPost(id: 1234) {
        postId
        title
        content
        author {
            id
            name
        }
    }
}

Then the full context variable is available when a response handler is evaluated:


{
  "arguments" : {
    id: "1234"
  },
  "source": {},
  "result" : {
      "postId": "1234",
      "title": "Some title",
      "content": "Some content",
      "author": {
        "id": "5678",
        "name": "Author Name"
      }
  },
  "identity" : {
      "sourceIp" : ["x.x.x.x"],
      "userArn" : "arn:aws:iam::123456789012:user/appsync",
      "accountId" : "666666666666",
      "user" : "AIDAAAAAAAAAAAAAAAAAA"
  }
}

prev.result

The result of whatever previous operation was executed in a pipeline resolver.

If the previous operation was the pipeline resolver's request handler, then ctx.prev.result represents that evaluation result and is made available to the first function in the pipeline.

If the previous operation was the first function, then ctx.prev.result represents the evaluation result of the first function response handler and is made available to the second function in the pipeline.

If the previous operation was the last function, then ctx.prev.result represents the evaluation result of the last function and is made available to the pipeline resolver's response handler.

info

An object that contains information about the GraphQL request. For the structure of this field, see Info.

Identity

The identity section contains information about the caller. The shape of this section depends on the authorization type of your AWS AppSync API.

For more information about AWS AppSync security options, see Authorization and authentication.

API_KEY authorization

The identity field isn't populated.

AWS_LAMBDA authorization

The identity has the following form:


type AppSyncIdentityLambda = {
  resolverContext: any;
};

The identity contains the resolverContext key, containing the same resolverContext content returned by the Lambda function authorizing the request.

AWS_IAM authorization

The identity has the following form:


type AppSyncIdentityIAM = {
  accountId: string;
  cognitoIdentityPoolId: string;
  cognitoIdentityId: string;
  sourceIp: string[];
  username: string;
  userArn: string;
  cognitoIdentityAuthType: string;
  cognitoIdentityAuthProvider: string;
};

AMAZON_COGNITO_USER_POOLS authorization

The identity has the following form:


type AppSyncIdentityCognito = {
  sourceIp: string[];
  username: string;
  groups: string[] | null;
  sub: string;
  issuer: string;
  claims: any;
  defaultAuthStrategy: string;
};

Each field is defined as follows:

accountId: The AWS account ID of the caller.
claims: The claims that the user has.
cognitoIdentityAuthType: Either authenticated or unauthenticated based on the identity type.
cognitoIdentityAuthProvider: A comma-separated list of external identity provider information used in obtaining the credentials used to sign the request.
cognitoIdentityId: The Amazon Cognito identity ID of the caller.
cognitoIdentityPoolId: The Amazon Cognito identity pool ID associated with the caller.
defaultAuthStrategy: The default authorization strategy for this caller (ALLOW or DENY).
issuer: The token issuer.
sourceIp: The source IP address of the caller that AWS AppSync receives. If the request doesn't include the x-forwarded-for header, the source IP value contains only a single IP address from the TCP connection. If the request includes a x-forwarded-for header, the source IP is a list of IP addresses from the x-forwarded-for header, in addition to the IP address from the TCP connection.
sub: The UUID of the authenticated user.
user: The IAM user.
userArn: The Amazon Resource Name (ARN) of the IAM user.
username: The user name of the authenticated user. In the case of AMAZON_COGNITO_USER_POOLS authorization, the value of username is the value of attribute cognito:username. In the case of AWS_IAM authorization, the value of username is the value of the AWS user principal. If you're using IAM authorization with credentials vended from Amazon Cognito identity pools, we recommend that you use cognitoIdentityId.

Access request headers

AWS AppSync supports passing custom headers from clients and accessing them in your GraphQL resolvers by using ctx.request.headers. You can then use the header values for actions such as inserting data into a data source or authorization checks. You can use single or multiple request headers using $curl with an API key from the command line, as shown in the following examples:

Single header example

Suppose you set a header of custom with a value of nadia like the following:


curl -XPOST -H "Content-Type:application/graphql" -H "custom:nadia" -H "x-api-key:<API-KEY-VALUE>" -d '{"query":"mutation { createEvent(name: \"demo\", when: \"Next Friday!\", where: \"Here!\") {id name when where description}}"}' https://<ENDPOINT>/graphql

This could then be accessed with ctx.request.headers.custom. For example, it might be in the following code for DynamoDB:


"custom": util.dynamodb.toDynamoDB(ctx.request.headers.custom)

Multiple header example

You can also pass multiple headers in a single request and access these in the resolver handler. For example, if the custom header is set with two values:


curl -XPOST -H "Content-Type:application/graphql" -H "custom:bailey" -H "custom:nadia" -H "x-api-key:<API-KEY-VALUE>" -d '{"query":"mutation { createEvent(name: \"demo\", when: \"Next Friday!\", where: \"Here!\") {id name when where description}}"}' https://<ENDPOINT>/graphql

You could then access these as an array, such as ctx.request.headers.custom[1].

Note

AWS AppSync doesn't expose the cookie header in ctx.request.headers.

Access the request custom domain name

AWS AppSync supports configuring a custom domain that you can use to access your GraphQL and real-time endpoints for your APIs. When making a request with a custom domain name, you can get the domain name using ctx.request.domainName.

When using the default GraphQL endpoint domain name, the value is null.

Info

The info section contains information about the GraphQL request. This section has the following form:


type Info = {
  fieldName: string;
  parentTypeName: string;
  variables: any;
  selectionSetList: string[];
  selectionSetGraphQL: string;
};

Each field is defined as follows:

fieldName: The name of the field that is currently being resolved.
parentTypeName: The name of the parent type for the field that is currently being resolved.
variables: A map which holds all variables that are passed into the GraphQL request.
selectionSetList: A list representation of the fields in the GraphQL selection set. Fields that are aliased are referenced only by the alias name, not the field name. The following example shows this in detail.
selectionSetGraphQL: A string representation of the selection set, formatted as GraphQL schema definition language (SDL). Although fragments aren't merged into the selection set, inline fragments are preserved, as shown in the following example.

Note

JSON.stringify will not include selectionSetGraphQL and selectionSetList in the string serialization. You must reference these properties directly.

For example, if you are resolving the getPost field of the following query:


query {
  getPost(id: $postId) {
    postId
    title
    secondTitle: title
    content
    author(id: $authorId) {
      authorId
      name
    }
    secondAuthor(id: "789") {
      authorId
    }
    ... on Post {
      inlineFrag: comments: {
        id
      }
    }
    ... postFrag
  }
}

fragment postFrag on Post {
  postFrag: comments: {
    id
  }
}

Then the full ctx.info variable that is available when processing a handler might be:


{
  "fieldName": "getPost",
  "parentTypeName": "Query",
  "variables": {
    "postId": "123",
    "authorId": "456"
  },
  "selectionSetList": [
    "postId",
    "title",
    "secondTitle"
    "content",
    "author",
    "author/authorId",
    "author/name",
    "secondAuthor",
    "secondAuthor/authorId",
    "inlineFragComments",
    "inlineFragComments/id",
    "postFragComments",
    "postFragComments/id"
  ],
  "selectionSetGraphQL": "{\n  getPost(id: $postId) {\n    postId\n    title\n    secondTitle: title\n    content\n    author(id: $authorId) {\n      authorId\n      name\n    }\n    secondAuthor(id: \"789\") {\n      authorId\n    }\n    ... on Post {\n      inlineFrag: comments {\n        id\n      }\n    }\n    ... postFrag\n  }\n}"
}

selectionSetList exposes only fields that belong to the current type. If the current type is an interface or union, only selected fields that belong to the interface are exposed. For example, given the following schema:


type Query {
    node(id: ID!): Node
}

interface Node {
    id: ID
}

type Post implements Node {
    id: ID
    title: String
    author: String
}

type Blog implements Node {
    id: ID
    title: String
    category: String
}

And the following query:


query {
    node(id: "post1") {
        id
        ... on Post {
            title
        }

        ... on Blog {
            title
        }
    }
}

When calling ctx.info.selectionSetList at the Query.node field resolution, only id is exposed:


"selectionSetList": [
    "id"
]

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Document Conventions

Choosing between direct data source access and proxying via a Lambda data source

JavaScript runtime features for resolvers and functions

AWS AppSync JavaScript resolver context object reference

Accessing the context

Note

context fields

Note

Identity

Access request headers

Note

Access the request custom domain name

Info

Note

Accessing the `context`

`context` fields