# PutItem
<a name="js-aws-appsync-resolver-reference-dynamodb-putitem"></a>

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
<a name="js-putitem-list"></a>

### PutItem fields list
<a name="js-putitem-list-col"></a>

 **`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)](https://docs.aws.amazon.com/appsync/latest/devguide/js-resolver-reference-dynamodb.html#js-aws-appsync-resolver-reference-dynamodb-typed-values-request). 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)](https://docs.aws.amazon.com/appsync/latest/devguide/js-resolver-reference-dynamodb.html#js-aws-appsync-resolver-reference-dynamodb-typed-values-request). 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](https://docs.aws.amazon.com/appsync/latest/devguide/js-resolver-reference-dynamodb.html#js-aws-appsync-resolver-reference-dynamodb-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](https://docs.aws.amazon.com/appsync/latest/devguide/conflict-detection-and-sync.html) 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](https://docs.aws.amazon.com/appsync/latest/devguide/conflict-detection-and-sync.html) 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)](https://docs.aws.amazon.com/appsync/latest/devguide/js-resolver-reference-dynamodb.html#js-aws-appsync-resolver-reference-dynamodb-typed-values-responses).

For more information about JavaScript resolvers, see [JavaScript resolvers overview](https://docs.aws.amazon.com/appsync/latest/devguide/resolver-reference-overview-js.html).

## Example 1
<a name="js-example-1"></a>

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
<a name="js-example-2"></a>

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](https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_PutItem.html).