BatchGetItem in DynamoDB

Introduction

BatchGetItem lets you get many items from one or more tables in a single request. It saves time and effort compared to asking for each item one by one.

You want to fetch multiple records by their keys quickly.

You need to get data from different tables at once.

You want to reduce the number of calls to the database to save time.

You have a list of user IDs and want to get their profiles in one go.

You want to load details for many products by their IDs together.

Syntax

DynamoDB

BatchGetItem {
  RequestItems: {
    TableName1: {
      Keys: [ {PrimaryKeyName: {S|N|B: value}}, ... ],
      ProjectionExpression: "attribute1, attribute2",  # optional
      ConsistentRead: true|false  # optional
    },
    TableName2: { ... }
  },
  ReturnConsumedCapacity: "INDEXES"|"TOTAL"|"NONE"  # optional
}

Keys is an array of primary key objects to fetch.

ProjectionExpression lets you get only certain attributes to save data transfer.

Examples

Get two users by their UserId from the Users table.

DynamoDB

BatchGetItem {
  RequestItems: {
    "Users": {
      Keys: [ { "UserId": {"S": "123"} }, { "UserId": {"S": "456"} } ]
    }
  }
}

Get product names and prices for two products and one order by their IDs from two tables.

DynamoDB

BatchGetItem {
  RequestItems: {
    "Products": {
      Keys: [ { "ProductId": {"S": "A1"} }, { "ProductId": {"S": "B2"} } ],
      ProjectionExpression: "Name, Price"
    },
    "Orders": {
      Keys: [ { "OrderId": {"S": "O100"} } ]
    }
  }
}

Sample Program

This command fetches the UserId and Email attributes for two users with IDs 'user1' and 'user2' from the Users table.

DynamoDB

aws dynamodb batch-get-item --request-items '{
  "Users": {
    "Keys": [
      {"UserId": {"S": "user1"}},
      {"UserId": {"S": "user2"}}
    ],
    "ProjectionExpression": "UserId, Email"
  }
}'

Important Notes

BatchGetItem can return fewer items than requested if some keys are not found.

If you request too many items, DynamoDB may return UnprocessedKeys to retry later.

Use ProjectionExpression to reduce data size and improve speed.

Summary

BatchGetItem fetches multiple items from one or more tables in one request.

It uses primary keys to find items quickly.

It helps reduce the number of calls and speeds up data retrieval.