Conditional Update in DynamoDB Using Java (Guide w/ Code Examples)

DynamoDB provides the ability to update an item conditionally based on certain conditions. You can use the updateItem method with a condition expression in Java. In the below example, the updateItem method is used to update an item in a table named "Product." The key of the item to update is specified using the key map, which maps attribute names to attribute values.

The updateExpression parameter is used to specify the update to be performed on the item. The expressionAttributeValues map provides the values for any placeholders in the update expression. The conditionExpression parameter is used to specify a condition that must be true for the update to be performed. If the condition is not true, the update will be skipped, and no error will be returned.

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.model.AttributeValue.AttributeValue;
import com.amazonaws.services.dynamodbv2.model.AttributeValue.M;
import com.amazonaws.services.dynamodbv2.model.UpdateItemRequest;

import java.util.Map;

public class ConditionalUpdateExample {
    public static void main(String[] args) {
        // Create a new client
        AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();

        // Define the key of the item to update
        Map<String, AttributeValue> key = new HashMap<String, AttributeValue>();
        key.put("id", new AttributeValue().withS("123"));

        // Define the update expression
        String updateExpression = "SET price = :newPrice, quantity = :newQuantity";

        // Define the values for the update expression
        Map<String, AttributeValue> expressionAttributeValues = new HashMap<String, AttributeValue>();
        expressionAttributeValues.put(":newPrice", new AttributeValue().withN("999"));
        expressionAttributeValues.put(":newQuantity", new AttributeValue().withN("20"));

        // Define the condition expression
        String conditionExpression = "quantity < :oldQuantity";

        // Define the values for the condition expression
        Map<String, AttributeValue> expressionAttributeValues = new HashMap<String, AttributeValue>();
        expressionAttributeValues.put(":oldQuantity", new AttributeValue().withN("50"));

        // Create the update request
        UpdateItemRequest request = new UpdateItemRequest()
                .withTableName("Product")
                .withKey(key)
                .withUpdateExpression(updateExpression)
                .withExpressionAttributeValues(expressionAttributeValues)
                .withConditionExpression(conditionExpression);

        // Send the request to update the item
        client.updateItem(request);
    }
}