# TransactGetItems
<a name="js-aws-appsync-resolver-reference-dynamodb-transact-get-items"></a>

The `TransactGetItems` request object lets you to tell the AWS AppSync DynamoDB function to make a `TransactGetItems` request to DynamoDB to retrieve multiple items, potentially across multiple tables. For this request object, you must specify the following:
+ The table name of each request item where to retrieve the item from
+ The key of each request item to retrieve from each table

The DynamoDB `TransactGetItems` limits apply and **no condition expression** can be provided.

The `TransactGetItems` request object has the following structure:

```
type DynamoDBTransactGetItemsRequest = {
  operation: 'TransactGetItems';
  transactItems: { table: string; key: { [key: string]: any }; projection?: { expression: string; expressionNames?: { [key: string]: string }; }[];
  };
};
```

The fields are defined as follows:

## TransactGetItems fields
<a name="js-TransactGetItems-list"></a>

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

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

** `transactItems` **  
The request items to include. The value is an array of request items. At least one request item must be provided. This `transactItems` value is required.    
** `table` **  
The DynamoDB table to retrieve the item from. The value is a string of the table name. This `table` value is required.  
** `key` **  
The DynamoDB key representing the primary key of the item to retrieve. 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).  
**`projection`**  
A projection that's used to specify the attributes to return from the DynamoDB operation. For more information about projections, see [Projections](https://docs.aws.amazon.com/appsync/latest/devguide/js-resolver-reference-dynamodb.html#js-aws-appsync-resolver-reference-dynamodb-projections). This field is optional.

Things to remember:
+ If a transaction succeeds, the order of retrieved items in the `items` block will be the same as the order of request items.
+ Transactions are performed in an all-or-nothing way. If any request item causes an error, the whole transaction will not be performed and error details will be returned.
+ A request item being unable to be retrieved is not an error. Instead, a *null* element appears in the *items* block in the corresponding position.
+ If the error of a transaction is *TransactionCanceledException*, the `cancellationReasons` block will be populated. The order of cancellation reasons in `cancellationReasons` block will be the same as the order of request items.
+  `TransactGetItems` is limited to 100 request items.

For the following example function request handler:

```
import { util } from '@aws-appsync/utils';

export function request(ctx) {
  const { authorId, postId } = ctx.args;
  return {
    operation: 'TransactGetItems',
    transactItems: [
      {
        table: 'posts',
        key: util.dynamodb.toMapValues({ postId }),
      },
      {
        table: 'authors',
        key: util.dynamodb.toMapValues({ authorId }),
      },
    ],
  };
}
```

If the transaction succeeds and only the first requested item is retrieved, the invocation result available in `ctx.result` is as follows:

```
{
    "items": [
       {
           // Attributes of the first requested item
           "post_id": "p1",
           "post_title": "title",
           "post_description": "description"
       },
       // Could not retrieve the second requested item
       null,
    ],
    "cancellationReasons": null
}
```

If the transaction fails due to *TransactionCanceledException* caused by the first request item, the invocation result available in `ctx.result` is as follows:

```
{
    "items": null,
    "cancellationReasons": [
       {
           "type":"Sample error type",
           "message":"Sample error message"
       },
       {
           "type":"None",
           "message":"None"
       }
    ]
}
```

The `ctx.error` contains details about the error. The keys **items** and **cancellationReasons** are guaranteed to be present in `ctx.result`.