PutItem

The PutItem request mapping document lets you tell the AWS AppSync DynamoDB function to make a PutItem request to DynamoDB, and enables you to specify the following:

• The key of the item in DynamoDB

• The full contents of the item (composed of key and attributeValues)

• Conditions for the operation to succeed

The PutItem request has the following structure:

type DynamoDBPutItemRequest = {
  operation: 'PutItem';
  key: { [key: string]: any };
  attributeValues: { [key: string]: any};
  condition?: ConditionCheckExpression;
  customPartitionKey?: string;
  populateIndexFields?: boolean;
  _version?: number;
};

The fields are defined as follows:

PutItem fields

PutItem fields list

operation

The DynamoDB operation to perform. To perform the PutItem DynamoDB operation, this must be set to PutItem. This value is required.

key

The key of the item in DynamoDB. DynamoDB items may have a single hash key, or a hash key and sort key, depending on the table structure. For more information about how to specify a “typed value”, see Type system (request mapping). This value is required.

attributeValues

The rest of the attributes of the item to be put into DynamoDB. For more information about how to specify a “typed value”, see Type system (request mapping). This field is optional.

condition

A condition to determine if the request should succeed or not, based on the state of the object already in DynamoDB. If no condition is specified, the PutItem request overwrites any existing entry for that item. For more information about conditions, see Condition expressions. This value is optional.

_version

A numeric value that represents the latest known version of an item. This value is optional. This field is used for Conflict Detection and is only supported on versioned data sources.

customPartitionKey

When enabled, this string value modifies the format of the ds_sk and ds_pk records used by the delta sync table when versioning has been enabled (for more information, see Conflict detection and sync in the AWS AppSync Developer Guide). When enabled, the processing of the populateIndexFields entry is also enabled. This field is optional.

populateIndexFields

A boolean value that, when enabled along with the customPartitionKey, creates new entries for each record in the delta sync table, specifically in the gsi_ds_pk and gsi_ds_sk columns. For more information, see Conflict detection and sync in the AWS AppSync Developer Guide. This field is optional.

The item written to DynamoDB is automatically converted to GraphQL and JSON primitive types and is available in the context result (context.result).

The item written to DynamoDB is automatically converted into GraphQL and JSON primitive types and is available in the context result (context.result).

For more information about DynamoDB type conversion, see Type system (response mapping).

For more information about JavaScript resolvers, see JavaScript resolvers overview.

Example 1

The following example is a function request handler for a GraphQL mutation updateThing(foo: String!, bar: String!, name: String!, version: Int!).

If no item with the specified key exists, it’s created. If an item already exists with the specified key, it’s overwritten.

import { util } from '@aws-appsync/utils';
export function request(ctx) {
  const { foo, bar, ...values} = ctx.args
  return {
    operation: 'PutItem',
    key: util.dynamodb.toMapValues({foo, bar}),
    attributeValues: util.dynamodb.toMapValues(values),
  };
}

Example 2

The following example is a function request handler for a GraphQL mutation updateThing(foo: String!, bar: String!, name: String!, expectedVersion: Int!).

This example verifies that the item currently in DynamoDB has the version field set to expectedVersion.

import { util } from '@aws-appsync/utils';
export function request(ctx) {
  const { foo, bar, name, expectedVersion } = ctx.args;
  const values = { name, version: expectedVersion + 1 };
  let condition = util.transform.toDynamoDBConditionExpression({
    version: { eq: expectedVersion },
  });

  return {
    operation: 'PutItem',
    key: util.dynamodb.toMapValues({ foo, bar }),
    attributeValues: util.dynamodb.toMapValues(values),
    condition,
  };
}

For more information about the DynamoDB PutItem API, see the DynamoDB API documentation.