Why do AWS JavaScript SDK calls to DynamoDB fail with native data types?

Question

When I try to query Amazon DynamoDB using native JavaScript data types it fails (e.g. :zipcode below). For example, the following code fails with Error while fetching data: TypeError: Cannot read properties of undefined (reading '0').

import { DynamoDBClient, QueryCommand } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({});

await client.send(
  new QueryCommand({
    TableName: tableName,
    KeyConditionExpression: "zipcode = :zipcode ",
    ExpressionAttributeValues: {
      ":zipcode": "11111",
    },
    ConsistentRead: true,
  })
);

But the below code works.

import { DynamoDBClient, QueryCommand } from "@aws-sdk/client-dynamodb";

const client = new DynamoDBClient({});

docClient.send(
  new QueryCommand({
    TableName: tableName,
    KeyConditionExpression: "zipcode = :zipcode ",
    ExpressionAttributeValues: {
      ":zipcode": { "S": "11111" },
    },
    ConsistentRead: true,
  })
);

What is this { "S": <value> } syntax and why is it needed?

Answer 1

Your second version of the syntax is correct. DynamoDB needs to know what data type you're sending it. The S in { "S": "1111" } indicates that you're sending a string. You can see a full list of the data type descriptors here.

Optionally, if you want to use your first syntax, you can use the Document Client.

V3

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

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

docClient.send(
  new QueryCommand({
    TableName: tableName,
    KeyConditionExpression: "zipcode = :zipcode",
    ExpressionAttributeValues: {
      ":zipcode": "11111",
    },
    ConsistentRead: true,
  })
);

V2

import * as AWS from "aws-sdk";

var params = {
  TableName: "Table",
  KeyConditionExpression: "zipcode = :zipcode",
  ExpressionAttributeValues: {
    ":zipcode": "11111",
  }
};

var documentClient = new AWS.DynamoDB.DocumentClient();

documentClient.query(params, function(err, data) {
   if (err) console.log(err);
   else console.log(data);
});

The Code Library for the JS SDK has multiple examples showcasing this syntax.