@aws-sdk/lib-dynamodb

Overview

The document client simplifies working with items in Amazon DynamoDB by abstracting away the notion of attribute values. This abstraction annotates native JavaScript types supplied as input parameters, as well as converts annotated response data to native JavaScript types.

Marshalling Input and Unmarshalling Response Data

The document client affords developers the use of native JavaScript types instead of AttributeValues to simplify the JavaScript development experience with Amazon DynamoDB. JavaScript objects passed in as parameters are marshalled into AttributeValue shapes required by Amazon DynamoDB. Responses from DynamoDB are unmarshalled into plain JavaScript objects by the DocumentClient. The DocumentClient does not accept AttributeValues in favor of native JavaScript types.

JavaScript Type	DynamoDB AttributeValue
String	S
Number / BigInt	N
Boolean	BOOL
null	NULL
Array	L
Object	M
Set<Uint8Array, Blob, ...>	BS
Set<Number, BigInt>	NS
Set<String>	SS
Uint8Array, Buffer, File, Blob...	B

Example

Here is an example list which is sent to DynamoDB client in an operation:

{ "L": [{ "NULL": true }, { "BOOL": false }, { "N": 1 }, { "S": "two" }] }

The DynamoDB document client abstracts the attribute values as follows in both input and output:

[null, false, 1, "two"]

Usage

To create document client you need to create DynamoDB client first as follows:

import { DynamoDBClient } from "@aws-sdk/client-dynamodb"; // ES6 import
// const { DynamoDBClient } = require("@aws-sdk/client-dynamodb"); // CommonJS import

// Bare-bones DynamoDB Client
const client = new DynamoDBClient({});

import { DynamoDB } from "@aws-sdk/client-dynamodb"; // ES6 import
// const { DynamoDB } = require("@aws-sdk/client-dynamodb"); // CommonJS import

// Full DynamoDB Client
const client = new DynamoDB({});

The bare-bones clients are more modular. They reduce bundle size and improve loading performance over full clients as explained in blog post on modular packages in AWS SDK for JavaScript.

Constructor

Once DynamoDB client is created, you can either create the bare-bones document client or full document client as follows:

import { DynamoDBDocumentClient } from "@aws-sdk/lib-dynamodb"; // ES6 import
// const { DynamoDBDocumentClient } = require("@aws-sdk/lib-dynamodb"); // CommonJS import

// Bare-bones document client
const ddbDocClient = DynamoDBDocumentClient.from(client); // client is DynamoDB client

import { DynamoDBDocument } from "@aws-sdk/lib-dynamodb"; // ES6 import
// const { DynamoDBDocument } = require("@aws-sdk/lib-dynamodb"); // CommonJS import

// Full document client
const ddbDocClient = DynamoDBDocument.from(client); // client is DynamoDB client

Configuration

The configuration for marshalling and unmarshalling can be sent as an optional second parameter during creation of document client as follows:

const marshallOptions = {
  // Whether to automatically convert empty strings, blobs, and sets to `null`.
  convertEmptyValues: false, // false, by default.
  // Whether to remove undefined values while marshalling.
  removeUndefinedValues: false, // false, by default.
  // Whether to convert typeof object to map attribute.
  convertClassInstanceToMap: false, // false, by default.
};

const unmarshallOptions = {
  // Whether to return numbers as a string instead of converting them to native JavaScript numbers.
  wrapNumbers: false, // false, by default.
};

const translateConfig = { marshallOptions, unmarshallOptions };

const client = new DynamoDBClient({});
const ddbDocClient = DynamoDBDocument.from(client, translateConfig);

Calling operations

You can call the document client operations using command objects on bare-bones client as follows:

import { DynamoDBDocumentClient, PutCommand } from "@aws-sdk/lib-dynamodb";

// ... DynamoDB client creation

const ddbDocClient = DynamoDBDocumentClient.from(client);
// Call using bare-bones client and Command object.
await ddbDocClient.send(
  new PutCommand({
    TableName,
    Item: {
      id: "1",
      content: "content from DynamoDBDocumentClient",
    },
  })
);

You can also call operations on full client as follows:

import { DynamoDBDocument } from "@aws-sdk/lib-dynamodb";

// ... DynamoDB client creation

const ddbDocClient = DynamoDBDocument.from(client);
// Call using full client.
await ddbDocClient.put({
  TableName,
  Item: {
    id: "2",
    content: "content from DynamoDBDocument",
  },
});

Client and Command middleware stacks

As with other AWS SDK for JavaScript v3 clients, you can apply middleware functions both on the client itself and individual Commands.

For individual Commands, here are examples of how to add middleware before and after both marshalling and unmarshalling. We will use QueryCommand as an example. Others follow the same pattern.

import { DynamoDBDocumentClient, QueryCommand } from "@aws-sdk/lib-dynamodb";

const client = new DynamoDBClient({
  /*...*/
});
const doc = DynamoDBDocumentClient.from(client);
const command = new QueryCommand({
  /*...*/
});

Before and after marshalling:

command.middlewareStack.addRelativeTo(
  (next) => async (args) => {
    console.log("pre-marshall", args.input);
    return next(args);
  },
  {
    relation: "before",
    toMiddleware: "DocumentMarshall",
  }
);
command.middlewareStack.addRelativeTo(
  (next) => async (args) => {
    console.log("post-marshall", args.input);
    return next(args);
  },
  {
    relation: "after",
    toMiddleware: "DocumentMarshall",
  }
);

Before and after unmarshalling:

command.middlewareStack.addRelativeTo(
  (next) => async (args) => {
    const result = await next(args);
    console.log("pre-unmarshall", result.output.Items);
    return result;
  },
  {
    relation: "after", // <- after for pre-unmarshall
    toMiddleware: "DocumentUnmarshall",
  }
);
command.middlewareStack.addRelativeTo(
  (next) => async (args) => {
    const result = await next(args);
    console.log("post-unmarshall", result.output.Items);
    return result;
  },
  {
    relation: "before", // <- before for post-unmarshall
    toMiddleware: "DocumentUnmarshall",
  }
);

Destroying document client

The destroy() call on document client is a no-op as document client does not create a new DynamoDB client. You need to call destroy() on DynamoDB client to clean resources used by it as shown below.

const client = new DynamoDBClient({});
const ddbDocClient = DynamoDBDocumentClient.from(client);

// Perform operations on document client.

ddbDocClient.destroy(); // no-op
client.destroy(); // destroys DynamoDBClient

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