UpdateItem basics in DynamoDB

Introduction

UpdateItem lets you change data in a DynamoDB table without replacing the whole item. It saves time and keeps your data accurate.

You want to change just one or two fields in a record without touching the rest.

You need to add a new attribute to an existing item.

You want to increase a number, like adding 1 to a counter.

You want to remove an attribute from an item.

You want to update an item only if it meets certain conditions.

Syntax

DynamoDB

UpdateItem {
  TableName: "TableName",
  Key: { "PrimaryKey": {S: "KeyValue"} },
  UpdateExpression: "SET #attr = :val",
  ExpressionAttributeNames: {"#attr": "AttributeName"},
  ExpressionAttributeValues: {":val": {S: "NewValue"}}
}

UpdateExpression tells DynamoDB what to change.

Use ExpressionAttributeNames and ExpressionAttributeValues to safely use attribute names and values.

Examples

Change the Name attribute of user with ID 123 to "Alice".

DynamoDB

UpdateItem {
  TableName: "Users",
  Key: { "UserID": {S: "123"} },
  UpdateExpression: "SET #name = :newName",
  ExpressionAttributeNames: {"#name": "Name"},
  ExpressionAttributeValues: {":newName": {S: "Alice"}}
}

Increase the Stock attribute by 5 for product A1.

DynamoDB

UpdateItem {
  TableName: "Products",
  Key: { "ProductID": {S: "A1"} },
  UpdateExpression: "ADD Stock :inc",
  ExpressionAttributeValues: {":inc": {N: "5"}}
}

Remove the DeliveryDate attribute from order 789.

DynamoDB

UpdateItem {
  TableName: "Orders",
  Key: { "OrderID": {S: "789"} },
  UpdateExpression: "REMOVE DeliveryDate"
}

Sample Program

This updates the Position of employee E001 to "Manager".

DynamoDB

UpdateItem {
  TableName: "Employees",
  Key: { "EmployeeID": {S: "E001"} },
  UpdateExpression: "SET #pos = :newPos",
  ExpressionAttributeNames: {"#pos": "Position"},
  ExpressionAttributeValues: {":newPos": {S: "Manager"}}
}

Important Notes

UpdateItem only changes specified attributes; others stay the same.

If the item does not exist, UpdateItem can create it if you use the right parameters.

Always use ExpressionAttributeNames and ExpressionAttributeValues to avoid errors with reserved words.

Summary

UpdateItem changes parts of an item without replacing it all.

Use UpdateExpression to specify what to change.

It is useful for adding, changing, or removing attributes safely.