TransactWriteItems in DynamoDB

Introduction

TransactWriteItems lets you make multiple changes to your database at once. It makes sure all changes happen together or none at all, so your data stays correct.

You want to update several related items and keep them in sync.

You need to add a new order and reduce stock at the same time.

You want to delete an item only if another item meets a condition.

You want to make sure no partial updates happen if something fails.

Syntax

DynamoDB

TransactWriteItems {
  TransactItems: [
    {
      Put: { TableName, Item },
      Update: { TableName, Key, UpdateExpression, ExpressionAttributeValues },
      Delete: { TableName, Key },
      ConditionCheck: { TableName, Key, ConditionExpression }
    },
    ...
  ]
}

You include an array of actions inside TransactItems.

Each action can be a Put, Update, Delete, or ConditionCheck.

Examples

This example adds a new user and decreases stock for a product in one transaction.

DynamoDB

TransactWriteItems {
  TransactItems: [
    { Put: { TableName: "Users", Item: { UserId: "123", Name: "Alice" } } },
    { Update: { TableName: "Inventory", Key: { ProductId: "A1" }, UpdateExpression: "SET Stock = Stock - :dec", ExpressionAttributeValues: { ":dec": { "N": "1" } } } }
  ]
}

This deletes a session only if the user exists.

DynamoDB

TransactWriteItems {
  TransactItems: [
    { Delete: { TableName: "Sessions", Key: { SessionId: "abc" } } },
    { ConditionCheck: { TableName: "Users", Key: { UserId: "123" }, ConditionExpression: "attribute_exists(UserId)" } }
  ]
}

Sample Program

This transaction adds a new order and reduces the stock of the product by 2. Both happen together or not at all.

DynamoDB

TransactWriteItems {
  TransactItems: [
    {
      Put: {
        TableName: "Orders",
        Item: { OrderId: "order123", ProductId: "prod456", Quantity: { "N": "2" } }
      }
    },
    {
      Update: {
        TableName: "Inventory",
        Key: { ProductId: "prod456" },
        UpdateExpression: "SET Stock = Stock - :qty",
        ExpressionAttributeValues: { ":qty": { "N": "2" } }
      }
    }
  ]
}

Important Notes

All actions in TransactWriteItems succeed or fail together.

Use ConditionCheck to prevent unwanted changes.

Maximum 100 actions per transaction.

Summary

TransactWriteItems lets you group multiple writes into one safe transaction.

It helps keep your data consistent by applying all changes together.

You can use Put, Update, Delete, and ConditionCheck actions inside it.