# Understand update expression order in DynamoDB with an AWS SDK
<a name="example_dynamodb_Scenario_UpdateExpressionOrder_section"></a>

The following code examples show how to understand update expression order.
+ Learn how DynamoDB processes update expressions.
+ Understand the order of operations in update expressions.
+ Avoid unexpected results by understanding expression evaluation.

------
#### [ Java ]

**SDK for Java 2.x**  
Demonstrate update expression order using AWS SDK for Java 2.x.  

```
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
import software.amazon.awssdk.services.dynamodb.model.GetItemRequest;
import software.amazon.awssdk.services.dynamodb.model.GetItemResponse;
import software.amazon.awssdk.services.dynamodb.model.ReturnValue;
import software.amazon.awssdk.services.dynamodb.model.UpdateItemRequest;
import software.amazon.awssdk.services.dynamodb.model.UpdateItemResponse;

import java.util.HashMap;
import java.util.Map;

    /**
     * Demonstrates the effect of update expression order.
     *
     * <p>This method shows how the order of operations in an update expression
     * affects the result of the update.
     *
     * @param dynamoDbClient The DynamoDB client
     * @param tableName The name of the DynamoDB table
     * @param key The key of the item to update
     * @return Map containing the results of different update orders
     * @throws DynamoDbException if an error occurs during the operation
     */
    public static Map<String, Object> demonstrateUpdateOrder(
        DynamoDbClient dynamoDbClient, String tableName, Map<String, AttributeValue> key) {

        Map<String, Object> results = new HashMap<>();

        try {
            // Initialize the item with a counter
            UpdateItemRequest initRequest = UpdateItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .updateExpression("SET Counter = :zero, OldCounter = :zero")
                .expressionAttributeValues(
                    Map.of(":zero", AttributeValue.builder().n("0").build()))
                .returnValues(ReturnValue.UPDATED_NEW)
                .build();

            dynamoDbClient.updateItem(initRequest);

            // Example 1: SET first, then ADD
            UpdateItemRequest setFirstRequest = UpdateItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .updateExpression("SET Counter = :value ADD OldCounter :increment")
                .expressionAttributeValues(Map.of(
                    ":value", AttributeValue.builder().n("10").build(),
                    ":increment", AttributeValue.builder().n("5").build()))
                .returnValues(ReturnValue.UPDATED_NEW)
                .build();

            UpdateItemResponse setFirstResponse = dynamoDbClient.updateItem(setFirstRequest);
            results.put("setFirstResponse", setFirstResponse);

            // Reset the item
            dynamoDbClient.updateItem(initRequest);

            // Example 2: ADD first, then SET
            UpdateItemRequest addFirstRequest = UpdateItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .updateExpression("ADD Counter :increment SET OldCounter = :value")
                .expressionAttributeValues(Map.of(
                    ":value", AttributeValue.builder().n("10").build(),
                    ":increment", AttributeValue.builder().n("5").build()))
                .returnValues(ReturnValue.UPDATED_NEW)
                .build();

            UpdateItemResponse addFirstResponse = dynamoDbClient.updateItem(addFirstRequest);
            results.put("addFirstResponse", addFirstResponse);

            // Reset the item
            dynamoDbClient.updateItem(initRequest);

            // Example 3: SET with multiple attributes
            UpdateItemRequest multiSetRequest = UpdateItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .updateExpression("SET Counter = :value, OldCounter = Counter")
                .expressionAttributeValues(
                    Map.of(":value", AttributeValue.builder().n("10").build()))
                .returnValues(ReturnValue.UPDATED_NEW)
                .build();

            UpdateItemResponse multiSetResponse = dynamoDbClient.updateItem(multiSetRequest);
            results.put("multiSetResponse", multiSetResponse);

            // Reset the item
            dynamoDbClient.updateItem(initRequest);

            // Example 4: SET with expression using the same attribute
            UpdateItemRequest selfReferenceRequest = UpdateItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .updateExpression("SET Counter = Counter + :increment, OldCounter = Counter")
                .expressionAttributeValues(
                    Map.of(":increment", AttributeValue.builder().n("5").build()))
                .returnValues(ReturnValue.UPDATED_NEW)
                .build();

            UpdateItemResponse selfReferenceResponse = dynamoDbClient.updateItem(selfReferenceRequest);
            results.put("selfReferenceResponse", selfReferenceResponse);

            results.put("success", true);

        } catch (DynamoDbException e) {
            results.put("success", false);
            results.put("error", e.getMessage());
        }

        return results;
    }

    /**
     * Updates an item with SET first, then REMOVE.
     *
     * <p>This method demonstrates updating an item with SET operation first,
     * followed by a REMOVE operation.
     *
     * @param dynamoDbClient The DynamoDB client
     * @param tableName The name of the DynamoDB table
     * @param key The key of the item to update
     * @param attributeToSet The attribute to set
     * @param setValue The value to set
     * @param attributeToRemove The attribute to remove
     * @return The response from DynamoDB
     * @throws DynamoDbException if an error occurs during the operation
     */
    public static UpdateItemResponse updateWithSetFirst(
        DynamoDbClient dynamoDbClient,
        String tableName,
        Map<String, AttributeValue> key,
        String attributeToSet,
        AttributeValue setValue,
        String attributeToRemove) {

        // Define the update parameters
        UpdateItemRequest request = UpdateItemRequest.builder()
            .tableName(tableName)
            .key(key)
            .updateExpression("SET #setAttr = :setValue REMOVE #removeAttr")
            .expressionAttributeNames(Map.of(
                "#setAttr", attributeToSet,
                "#removeAttr", attributeToRemove))
            .expressionAttributeValues(Map.of(":setValue", setValue))
            .returnValues(ReturnValue.UPDATED_NEW)
            .build();

        // Perform the update operation
        try {
            return dynamoDbClient.updateItem(request);
        } catch (DynamoDbException e) {
            throw DynamoDbException.builder()
                .message("Failed to update item with SET first: " + e.getMessage())
                .cause(e)
                .build();
        }
    }

    /**
     * Updates an item with REMOVE first, then SET.
     *
     * <p>This method demonstrates updating an item with REMOVE operation first,
     * followed by a SET operation.
     *
     * @param dynamoDbClient The DynamoDB client
     * @param tableName The name of the DynamoDB table
     * @param key The key of the item to update
     * @param attributeToSet The attribute to set
     * @param setValue The value to set
     * @param attributeToRemove The attribute to remove
     * @return The response from DynamoDB
     * @throws DynamoDbException if an error occurs during the operation
     */
    public static UpdateItemResponse updateWithRemoveFirst(
        DynamoDbClient dynamoDbClient,
        String tableName,
        Map<String, AttributeValue> key,
        String attributeToSet,
        AttributeValue setValue,
        String attributeToRemove) {

        // Define the update parameters
        UpdateItemRequest request = UpdateItemRequest.builder()
            .tableName(tableName)
            .key(key)
            .updateExpression("REMOVE #removeAttr SET #setAttr = :setValue")
            .expressionAttributeNames(Map.of(
                "#setAttr", attributeToSet,
                "#removeAttr", attributeToRemove))
            .expressionAttributeValues(Map.of(":setValue", setValue))
            .returnValues(ReturnValue.UPDATED_NEW)
            .build();

        // Perform the update operation
        try {
            return dynamoDbClient.updateItem(request);
        } catch (DynamoDbException e) {
            throw DynamoDbException.builder()
                .message("Failed to update item with REMOVE first: " + e.getMessage())
                .cause(e)
                .build();
        }
    }

    /**
     * Updates an item with all operation types in a specific order.
     *
     * <p>This method demonstrates using all operation types (SET, REMOVE, ADD, DELETE)
     * in a specific order in a single update expression.
     *
     * @param dynamoDbClient The DynamoDB client
     * @param tableName The name of the DynamoDB table
     * @param key The key of the item to update
     * @return The response from DynamoDB
     * @throws DynamoDbException if an error occurs during the operation
     */
    public static UpdateItemResponse updateWithAllOperationTypes(
        DynamoDbClient dynamoDbClient, String tableName, Map<String, AttributeValue> key) {

        // Define the update parameters
        UpdateItemRequest request = UpdateItemRequest.builder()
            .tableName(tableName)
            .key(key)
            .updateExpression("SET #stringAttr = :stringVal, #mapAttr.#nestedAttr = :nestedVal " + "REMOVE #oldAttr "
                + "ADD #counterAttr :increment "
                + "DELETE #stringSetAttr :stringSetVal")
            .expressionAttributeNames(Map.of(
                "#stringAttr", "StringAttribute",
                "#mapAttr", "MapAttribute",
                "#nestedAttr", "NestedAttribute",
                "#oldAttr", "OldAttribute",
                "#counterAttr", "CounterAttribute",
                "#stringSetAttr", "StringSetAttribute"))
            .expressionAttributeValues(Map.of(
                ":stringVal", AttributeValue.builder().s("New Value").build(),
                ":nestedVal", AttributeValue.builder().s("Nested Value").build(),
                ":increment", AttributeValue.builder().n("1").build(),
                ":stringSetVal", AttributeValue.builder().ss("Value1").build()))
            .returnValues(ReturnValue.UPDATED_NEW)
            .build();

        // Perform the update operation
        try {
            return dynamoDbClient.updateItem(request);
        } catch (DynamoDbException e) {
            throw DynamoDbException.builder()
                .message("Failed to update item with all operation types: " + e.getMessage())
                .cause(e)
                .build();
        }
    }

    /**
     * Gets the current state of an item.
     *
     * <p>Helper method to retrieve the current state of an item.
     *
     * @param dynamoDbClient The DynamoDB client
     * @param tableName The name of the DynamoDB table
     * @param key The key of the item to get
     * @return The item or null if not found
     * @throws DynamoDbException if an error occurs during the operation
     */
    public static Map<String, AttributeValue> getItem(
        DynamoDbClient dynamoDbClient, String tableName, Map<String, AttributeValue> key) {

        // Define the get parameters
        GetItemRequest request =
            GetItemRequest.builder().tableName(tableName).key(key).build();

        // Perform the get operation
        try {
            GetItemResponse response = dynamoDbClient.getItem(request);

            // Return the item if it exists, otherwise null
            return response.item();
        } catch (DynamoDbException e) {
            throw DynamoDbException.builder()
                .message("Failed to get item: " + e.getMessage())
                .cause(e)
                .build();
        }
    }
```
Example usage of update expression order with AWS SDK for Java 2.x.  

```
    public static void exampleUsage(DynamoDbClient dynamoDbClient, String tableName) {
        // Example key
        Map<String, AttributeValue> key = new HashMap<>();
        key.put("ProductId", AttributeValue.builder().s("P12345").build());

        System.out.println("Demonstrating update expression order in DynamoDB");

        try {
            // Example 1: Demonstrate update order effects
            System.out.println("\nExample 1: Demonstrating update order effects");
            Map<String, Object> orderResults = demonstrateUpdateOrder(dynamoDbClient, tableName, key);

            if ((boolean) orderResults.get("success")) {
                System.out.println("SET first, then ADD:");
                System.out.println("  " + orderResults.get("setFirstResponse"));

                System.out.println("ADD first, then SET:");
                System.out.println("  " + orderResults.get("addFirstResponse"));

                System.out.println("SET with multiple attributes:");
                System.out.println("  " + orderResults.get("multiSetResponse"));

                System.out.println("SET with self-reference:");
                System.out.println("  " + orderResults.get("selfReferenceResponse"));
            } else {
                System.out.println("Error: " + orderResults.get("error"));
            }

            // Example 2: Update with SET first, then REMOVE
            System.out.println("\nExample 2: Update with SET first, then REMOVE");
            UpdateItemResponse setFirstResponse = updateWithSetFirst(
                dynamoDbClient,
                tableName,
                key,
                "Status",
                AttributeValue.builder().s("Active").build(),
                "OldStatus");

            System.out.println("Updated attributes: " + setFirstResponse.attributes());

            // Example 3: Update with REMOVE first, then SET
            System.out.println("\nExample 3: Update with REMOVE first, then SET");
            UpdateItemResponse removeFirstResponse = updateWithRemoveFirst(
                dynamoDbClient,
                tableName,
                key,
                "Status",
                AttributeValue.builder().s("Inactive").build(),
                "OldStatus");

            System.out.println("Updated attributes: " + removeFirstResponse.attributes());

            // Example 4: Update with all operation types
            System.out.println("\nExample 4: Update with all operation types");
            UpdateItemResponse allOpsResponse = updateWithAllOperationTypes(dynamoDbClient, tableName, key);

            System.out.println("Updated attributes: " + allOpsResponse.attributes());

            // Example 5: Get the current state of the item
            System.out.println("\nExample 5: Current state of the item");
            Map<String, AttributeValue> item = getItem(dynamoDbClient, tableName, key);

            if (item != null) {
                System.out.println("Item: " + item);
            } else {
                System.out.println("Item not found");
            }

            // Explain update expression order
            System.out.println("\nKey points about update expression order in DynamoDB:");
            System.out.println("1. Update expressions are processed in this order: SET, REMOVE, ADD, DELETE");
            System.out.println("2. Within each clause, operations are processed from left to right");
            System.out.println("3. SET operations use the item state before any updates in the expression");
            System.out.println("4. When an attribute is referenced multiple times, the first operation wins");
            System.out.println("5. To reference a new value, split the update into multiple operations");
            System.out.println("6. The order of clauses in the expression doesn't change the evaluation order");
            System.out.println("7. For complex updates, consider using multiple separate update operations");

        } catch (DynamoDbException e) {
            System.err.println("Error: " + e.getMessage());
            e.printStackTrace();
        }
    }
```
+  For API details, see [UpdateItem](https://docs.aws.amazon.com/goto/SdkForJavaV2/dynamodb-2012-08-10/UpdateItem) in *AWS SDK for Java 2.x API Reference*. 

------
#### [ JavaScript ]

**SDK for JavaScript (v3)**  
Demonstrate update expression order using AWS SDK for JavaScript.  

```
const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { 
  DynamoDBDocumentClient, 
  UpdateCommand,
  GetCommand,
  PutCommand
} = require("@aws-sdk/lib-dynamodb");

/**
 * Update an item with multiple actions in a single update expression.
 * 
 * This function demonstrates how to use multiple actions in a single update expression
 * and how DynamoDB processes these actions.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to update
 * @param {string} updateExpression - The update expression with multiple actions
 * @param {Object} [expressionAttributeNames] - Expression attribute name placeholders
 * @param {Object} [expressionAttributeValues] - Expression attribute value placeholders
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateWithMultipleActions(
  config,
  tableName,
  key,
  updateExpression,
  expressionAttributeNames,
  expressionAttributeValues
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Prepare the update parameters
  const updateParams = {
    TableName: tableName,
    Key: key,
    UpdateExpression: updateExpression,
    ReturnValues: "UPDATED_NEW"
  };
  
  // Add expression attribute names if provided
  if (expressionAttributeNames) {
    updateParams.ExpressionAttributeNames = expressionAttributeNames;
  }
  
  // Add expression attribute values if provided
  if (expressionAttributeValues) {
    updateParams.ExpressionAttributeValues = expressionAttributeValues;
  }
  
  // Execute the update
  const response = await docClient.send(new UpdateCommand(updateParams));
  
  return response;
}

/**
 * Demonstrate that variables hold copies of existing values before modifications.
 * 
 * This function creates an item with initial values, then updates it with an expression
 * that uses the values of attributes before they are modified in the same expression.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to create and update
 * @returns {Promise<Object>} - A dictionary containing the results of the demonstration
 */
async function demonstrateValueCopying(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Step 1: Create an item with initial values
  const initialItem = { ...key, a: 1, b: 2, c: 3 };
  
  await docClient.send(new PutCommand({
    TableName: tableName,
    Item: initialItem
  }));
  
  // Step 2: Get the item to verify initial state
  const responseBefore = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemBefore = responseBefore.Item || {};
  
  // Step 3: Update the item with an expression that uses values before they are modified
  // This expression removes 'a', then sets 'b' to the value of 'a', and 'c' to the value of 'b'
  const updateResponse = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: "REMOVE a SET b = a, c = b",
    ReturnValues: "UPDATED_NEW"
  }));
  
  // Step 4: Get the item to verify final state
  const responseAfter = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemAfter = responseAfter.Item || {};
  
  // Return the results
  return {
    initialState: itemBefore,
    updateResponse: updateResponse,
    finalState: itemAfter
  };
}

/**
 * Demonstrate the order in which different action types are processed.
 * 
 * This function creates an item with initial values, then updates it with an expression
 * that includes multiple action types (SET, REMOVE, ADD, DELETE) to show the order
 * in which they are processed.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to create and update
 * @returns {Promise<Object>} - A dictionary containing the results of the demonstration
 */
async function demonstrateActionOrder(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Step 1: Create an item with initial values
  const initialItem = {
    ...key,
    counter: 10,
    set_attr: new Set(["A", "B", "C"]),
    to_remove: "This will be removed",
    to_modify: "Original value"
  };
  
  await docClient.send(new PutCommand({
    TableName: tableName,
    Item: initialItem
  }));
  
  // Step 2: Get the item to verify initial state
  const responseBefore = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemBefore = responseBefore.Item || {};
  
  // Step 3: Update the item with multiple action types
  // The actions will be processed in this order: REMOVE, SET, ADD, DELETE
  const updateResponse = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: "REMOVE to_remove SET to_modify = :new_value ADD counter :increment DELETE set_attr :elements",
    ExpressionAttributeValues: {
      ":new_value": "Updated value",
      ":increment": 5,
      ":elements": new Set(["B"])
    },
    ReturnValues: "UPDATED_NEW"
  }));
  
  // Step 4: Get the item to verify final state
  const responseAfter = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemAfter = responseAfter.Item || {};
  
  // Return the results
  return {
    initialState: itemBefore,
    updateResponse: updateResponse,
    finalState: itemAfter
  };
}

/**
 * Update multiple attributes with a single SET action.
 * 
 * This function demonstrates how to update multiple attributes in a single SET action,
 * which is more efficient than using multiple separate update operations.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to update
 * @param {Object} attributes - The attributes to update and their new values
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateWithMultipleSetActions(
  config,
  tableName,
  key,
  attributes
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Build the update expression and expression attribute values
  let updateExpression = "SET ";
  const expressionAttributeValues = {};
  
  // Add each attribute to the update expression
  Object.entries(attributes).forEach(([attrName, attrValue], index) => {
    const valuePlaceholder = `:val${index}`;
    
    if (index > 0) {
      updateExpression += ", ";
    }
    updateExpression += `${attrName} = ${valuePlaceholder}`;
    
    expressionAttributeValues[valuePlaceholder] = attrValue;
  });
  
  // Execute the update
  const response = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: updateExpression,
    ExpressionAttributeValues: expressionAttributeValues,
    ReturnValues: "UPDATED_NEW"
  }));
  
  return response;
}

/**
 * Update an attribute with a value from another attribute or a default value.
 * 
 * This function demonstrates how to use if_not_exists to conditionally copy a value
 * from one attribute to another, or use a default value if the source doesn't exist.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to update
 * @param {string} sourceAttribute - The attribute to copy the value from
 * @param {string} targetAttribute - The attribute to update
 * @param {any} defaultValue - The default value to use if the source attribute doesn't exist
 * @returns {Promise<Object>} - The response from DynamoDB
 */
async function updateWithConditionalValueCopying(
  config,
  tableName,
  key,
  sourceAttribute,
  targetAttribute,
  defaultValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Use if_not_exists to conditionally copy the value
  const response = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${targetAttribute} = if_not_exists(${sourceAttribute}, :default)`,
    ExpressionAttributeValues: {
      ":default": defaultValue
    },
    ReturnValues: "UPDATED_NEW"
  }));
  
  return response;
}

/**
 * Demonstrate complex update expressions with multiple operations on the same attribute.
 * 
 * This function shows how DynamoDB processes multiple operations on the same attribute
 * in a single update expression.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The primary key of the item to create and update
 * @returns {Promise<Object>} - A dictionary containing the results of the demonstration
 */
async function demonstrateMultipleOperationsOnSameAttribute(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Step 1: Create an item with initial values
  const initialItem = {
    ...key,
    counter: 10,
    list_attr: [1, 2, 3],
    map_attr: {
      nested1: "value1",
      nested2: "value2"
    }
  };
  
  await docClient.send(new PutCommand({
    TableName: tableName,
    Item: initialItem
  }));
  
  // Step 2: Get the item to verify initial state
  const responseBefore = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemBefore = responseBefore.Item || {};
  
  // Step 3: Update the item with multiple operations on the same attributes
  const updateResponse = await docClient.send(new UpdateCommand({
    TableName: tableName,
    Key: key,
    UpdateExpression: `
      SET counter = counter + :inc1,
          counter = counter + :inc2,
          map_attr.nested1 = :new_val1,
          map_attr.nested3 = :new_val3,
          list_attr[0] = list_attr[1],
          list_attr[1] = list_attr[2]
    `,
    ExpressionAttributeValues: {
      ":inc1": 5,
      ":inc2": 3,
      ":new_val1": "updated_value1",
      ":new_val3": "new_value3"
    },
    ReturnValues: "UPDATED_NEW"
  }));
  
  // Step 4: Get the item to verify final state
  const responseAfter = await docClient.send(new GetCommand({
    TableName: tableName,
    Key: key
  }));
  
  const itemAfter = responseAfter.Item || {};
  
  // Return the results
  return {
    initialState: itemBefore,
    updateResponse: updateResponse,
    finalState: itemAfter
  };
}
```
Example usage of update expression order with AWS SDK for JavaScript.  

```
/**
 * Example of how to use update expression order of operations in DynamoDB.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "OrderProcessing";
  
  console.log("Demonstrating update expression order of operations in DynamoDB");
  
  try {
    // Example 1: Demonstrating value copying in update expressions
    console.log("\nExample 1: Demonstrating value copying in update expressions");
    const results1 = await demonstrateValueCopying(
      config,
      tableName,
      { OrderId: "order123" }
    );
    
    console.log("Initial state:", JSON.stringify(results1.initialState, null, 2));
    console.log("Update response:", JSON.stringify(results1.updateResponse, null, 2));
    console.log("Final state:", JSON.stringify(results1.finalState, null, 2));
    
    console.log("\nExplanation:");
    console.log("1. The initial state had a=1, b=2, c=3");
    console.log("2. The update expression 'REMOVE a SET b = a, c = b' did the following:");
    console.log("   - Copied the value of 'a' (which was 1) to be used for 'b'");
    console.log("   - Copied the value of 'b' (which was 2) to be used for 'c'");
    console.log("   - Removed the attribute 'a'");
    console.log("3. The final state has b=1, c=2, and 'a' is removed");
    console.log("4. This demonstrates that DynamoDB uses the values of attributes as they were BEFORE any modifications");
    
    // Example 2: Demonstrating the order of different action types
    console.log("\nExample 2: Demonstrating the order of different action types");
    const results2 = await demonstrateActionOrder(
      config,
      tableName,
      { OrderId: "order456" }
    );
    
    console.log("Initial state:", JSON.stringify(results2.initialState, null, 2));
    console.log("Update response:", JSON.stringify(results2.updateResponse, null, 2));
    console.log("Final state:", JSON.stringify(results2.finalState, null, 2));
    
    console.log("\nExplanation:");
    console.log("1. The update expression contained multiple action types: REMOVE, SET, ADD, DELETE");
    console.log("2. DynamoDB processes these actions in this order: REMOVE, SET, ADD, DELETE");
    console.log("3. First, 'to_remove' was removed");
    console.log("4. Then, 'to_modify' was set to a new value");
    console.log("5. Next, 'counter' was incremented by 5");
    console.log("6. Finally, 'B' was removed from the set attribute");
    
    // Example 3: Updating multiple attributes in a single SET action
    console.log("\nExample 3: Updating multiple attributes in a single SET action");
    const response3 = await updateWithMultipleSetActions(
      config,
      tableName,
      { OrderId: "order789" },
      {
        Status: "Shipped",
        ShippingDate: "2025-05-28",
        TrackingNumber: "1Z999AA10123456784"
      }
    );
    
    console.log("Multiple attributes updated successfully:", JSON.stringify(response3.Attributes, null, 2));
    
    // Example 4: Conditional value copying with if_not_exists
    console.log("\nExample 4: Conditional value copying with if_not_exists");
    const response4 = await updateWithConditionalValueCopying(
      config,
      tableName,
      { OrderId: "order101" },
      "PreferredShippingMethod",
      "ShippingMethod",
      "Standard"
    );
    
    console.log("Conditional value copying result:", JSON.stringify(response4.Attributes, null, 2));
    
    // Example 5: Multiple operations on the same attribute
    console.log("\nExample 5: Multiple operations on the same attribute");
    const results5 = await demonstrateMultipleOperationsOnSameAttribute(
      config,
      tableName,
      { OrderId: "order202" }
    );
    
    console.log("Initial state:", JSON.stringify(results5.initialState, null, 2));
    console.log("Update response:", JSON.stringify(results5.updateResponse, null, 2));
    console.log("Final state:", JSON.stringify(results5.finalState, null, 2));
    
    console.log("\nExplanation:");
    console.log("1. The counter was incremented twice (first by 5, then by 3) for a total of +8");
    console.log("2. The map attribute had one value updated and a new nested attribute added");
    console.log("3. The list attribute had values shifted (value at index 1 moved to index 0, value at index 2 moved to index 1)");
    console.log("4. All operations within the SET action are processed from left to right");
    
    // Key points about update expression order of operations
    console.log("\nKey Points About Update Expression Order of Operations:");
    console.log("1. Variables in expressions hold copies of attribute values as they existed BEFORE any modifications");
    console.log("2. Multiple actions in an update expression are processed in this order: REMOVE, SET, ADD, DELETE");
    console.log("3. Within each action type, operations are processed from left to right");
    console.log("4. You can reference the same attribute multiple times in an expression");
    console.log("5. You can use if_not_exists() to conditionally set values based on attribute existence");
    console.log("6. Using a single update expression with multiple actions is more efficient than multiple separate updates");
    console.log("7. The update expression is atomic - either all actions succeed or none do");
    
  } catch (error) {
    console.error("Error:", error);
  }
}
```
+  For API details, see [UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand) in *AWS SDK for JavaScript API Reference*. 

------
#### [ Python ]

**SDK for Python (Boto3)**  
Demonstrate update expression order using AWS SDK for Python (Boto3).  

```
import boto3
import json
from typing import Any, Dict, Optional


def update_with_multiple_actions(
    table_name: str,
    key: Dict[str, Any],
    update_expression: str,
    expression_attribute_names: Optional[Dict[str, str]] = None,
    expression_attribute_values: Optional[Dict[str, Any]] = None,
) -> Dict[str, Any]:
    """
    Update an item with multiple actions in a single update expression.

    This function demonstrates how to use multiple actions in a single update expression
    and how DynamoDB processes these actions.

    Args:
        table_name (str): The name of the DynamoDB table.
        key (Dict[str, Any]): The primary key of the item to update.
        update_expression (str): The update expression with multiple actions.
        expression_attribute_names (Optional[Dict[str, str]]): Expression attribute name placeholders.
        expression_attribute_values (Optional[Dict[str, Any]]): Expression attribute value placeholders.

    Returns:
        Dict[str, Any]: The response from DynamoDB containing the updated attribute values.
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    # Prepare the update parameters
    update_params = {
        "Key": key,
        "UpdateExpression": update_expression,
        "ReturnValues": "UPDATED_NEW",
    }

    # Add expression attribute names if provided
    if expression_attribute_names:
        update_params["ExpressionAttributeNames"] = expression_attribute_names

    # Add expression attribute values if provided
    if expression_attribute_values:
        update_params["ExpressionAttributeValues"] = expression_attribute_values

    # Execute the update
    response = table.update_item(**update_params)

    return response


def demonstrate_value_copying(table_name: str, key: Dict[str, Any]) -> Dict[str, Any]:
    """
    Demonstrate that variables hold copies of existing values before modifications.

    This function creates an item with initial values, then updates it with an expression
    that uses the values of attributes before they are modified in the same expression.

    Args:
        table_name (str): The name of the DynamoDB table.
        key (Dict[str, Any]): The primary key of the item to create and update.

    Returns:
        Dict[str, Any]: A dictionary containing the results of the demonstration.
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    # Step 1: Create an item with initial values
    initial_item = key.copy()
    initial_item.update({"a": 1, "b": 2, "c": 3})

    table.put_item(Item=initial_item)

    # Step 2: Get the item to verify initial state
    response_before = table.get_item(Key=key)
    item_before = response_before.get("Item", {})

    # Step 3: Update the item with an expression that uses values before they are modified
    # This expression removes 'a', then sets 'b' to the value of 'a', and 'c' to the value of 'b'
    update_response = table.update_item(
        Key=key, UpdateExpression="REMOVE a SET b = a, c = b", ReturnValues="UPDATED_NEW"
    )

    # Step 4: Get the item to verify final state
    response_after = table.get_item(Key=key)
    item_after = response_after.get("Item", {})

    # Return the results
    return {
        "initial_state": item_before,
        "update_response": update_response,
        "final_state": item_after,
    }


def demonstrate_action_order(table_name: str, key: Dict[str, Any]) -> Dict[str, Any]:
    """
    Demonstrate the order in which different action types are processed.

    This function creates an item with initial values, then updates it with an expression
    that includes multiple action types (SET, REMOVE, ADD, DELETE) to show the order
    in which they are processed.

    Args:
        table_name (str): The name of the DynamoDB table.
        key (Dict[str, Any]): The primary key of the item to create and update.

    Returns:
        Dict[str, Any]: A dictionary containing the results of the demonstration.
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    # Step 1: Create an item with initial values
    initial_item = key.copy()
    initial_item.update(
        {
            "counter": 10,
            "set_attr": set(["A", "B", "C"]),
            "to_remove": "This will be removed",
            "to_modify": "Original value",
        }
    )

    table.put_item(Item=initial_item)

    # Step 2: Get the item to verify initial state
    response_before = table.get_item(Key=key)
    item_before = response_before.get("Item", {})

    # Step 3: Update the item with multiple action types
    # The actions will be processed in this order: REMOVE, SET, ADD, DELETE
    update_response = table.update_item(
        Key=key,
        UpdateExpression="REMOVE to_remove SET to_modify = :new_value ADD counter :increment DELETE set_attr :elements",
        ExpressionAttributeValues={
            ":new_value": "Updated value",
            ":increment": 5,
            ":elements": set(["B"]),
        },
        ReturnValues="UPDATED_NEW",
    )

    # Step 4: Get the item to verify final state
    response_after = table.get_item(Key=key)
    item_after = response_after.get("Item", {})

    # Return the results
    return {
        "initial_state": item_before,
        "update_response": update_response,
        "final_state": item_after,
    }


def update_with_multiple_set_actions(
    table_name: str, key: Dict[str, Any], attributes: Dict[str, Any]
) -> Dict[str, Any]:
    """
    Update multiple attributes with a single SET action.

    This function demonstrates how to update multiple attributes in a single SET action,
    which is more efficient than using multiple separate update operations.

    Args:
        table_name (str): The name of the DynamoDB table.
        key (Dict[str, Any]): The primary key of the item to update.
        attributes (Dict[str, Any]): The attributes to update and their new values.

    Returns:
        Dict[str, Any]: The response from DynamoDB containing the updated attribute values.
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    # Build the update expression and expression attribute values
    update_expression = "SET "
    expression_attribute_values = {}

    # Add each attribute to the update expression
    for i, (attr_name, attr_value) in enumerate(attributes.items()):
        value_placeholder = f":val{i}"

        if i > 0:
            update_expression += ", "
        update_expression += f"{attr_name} = {value_placeholder}"

        expression_attribute_values[value_placeholder] = attr_value

    # Execute the update
    response = table.update_item(
        Key=key,
        UpdateExpression=update_expression,
        ExpressionAttributeValues=expression_attribute_values,
        ReturnValues="UPDATED_NEW",
    )

    return response


def update_with_conditional_value_copying(
    table_name: str,
    key: Dict[str, Any],
    source_attribute: str,
    target_attribute: str,
    default_value: Any,
) -> Dict[str, Any]:
    """
    Update an attribute with a value from another attribute or a default value.

    This function demonstrates how to use if_not_exists to conditionally copy a value
    from one attribute to another, or use a default value if the source doesn't exist.

    Args:
        table_name (str): The name of the DynamoDB table.
        key (Dict[str, Any]): The primary key of the item to update.
        source_attribute (str): The attribute to copy the value from.
        target_attribute (str): The attribute to update.
        default_value (Any): The default value to use if the source attribute doesn't exist.

    Returns:
        Dict[str, Any]: The response from DynamoDB containing the updated attribute values.
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    # Use if_not_exists to conditionally copy the value
    response = table.update_item(
        Key=key,
        UpdateExpression=f"SET {target_attribute} = if_not_exists({source_attribute}, :default)",
        ExpressionAttributeValues={":default": default_value},
        ReturnValues="UPDATED_NEW",
    )

    return response
```
Example usage of update expression order with AWS SDK for Python (Boto3).  

```
def example_usage():
    """Example of how to use update expression order of operations in DynamoDB."""
    # Example parameters
    table_name = "OrderProcessing"
    key = {"OrderId": "order123"}

    print("Example 1: Demonstrating value copying in update expressions")
    try:
        results = demonstrate_value_copying(table_name=table_name, key=key)

        print(f"Initial state: {json.dumps(results['initial_state'], default=str)}")
        print(f"Update response: {json.dumps(results['update_response'], default=str)}")
        print(f"Final state: {json.dumps(results['final_state'], default=str)}")

        print("\nExplanation:")
        print("1. The initial state had a=1, b=2, c=3")
        print("2. The update expression 'REMOVE a SET b = a, c = b' did the following:")
        print("   - Copied the value of 'a' (which was 1) to be used for 'b'")
        print("   - Copied the value of 'b' (which was 2) to be used for 'c'")
        print("   - Removed the attribute 'a'")
        print("3. The final state has b=1, c=2, and 'a' is removed")
        print(
            "4. This demonstrates that DynamoDB uses the values of attributes as they were BEFORE any modifications"
        )
    except Exception as e:
        print(f"Error demonstrating value copying: {e}")

    print("\nExample 2: Demonstrating the order of different action types")
    try:
        results = demonstrate_action_order(table_name=table_name, key={"OrderId": "order456"})

        print(f"Initial state: {json.dumps(results['initial_state'], default=str)}")
        print(f"Update response: {json.dumps(results['update_response'], default=str)}")
        print(f"Final state: {json.dumps(results['final_state'], default=str)}")

        print("\nExplanation:")
        print("1. The update expression contained multiple action types: REMOVE, SET, ADD, DELETE")
        print("2. DynamoDB processes these actions in this order: REMOVE, SET, ADD, DELETE")
        print("3. First, 'to_remove' was removed")
        print("4. Then, 'to_modify' was set to a new value")
        print("5. Next, 'counter' was incremented by 5")
        print("6. Finally, 'B' was removed from the set attribute")
    except Exception as e:
        print(f"Error demonstrating action order: {e}")

    print("\nExample 3: Updating multiple attributes in a single SET action")
    try:
        response = update_with_multiple_set_actions(
            table_name=table_name,
            key={"OrderId": "order789"},
            attributes={
                "Status": "Shipped",
                "ShippingDate": "2025-05-14",
                "TrackingNumber": "1Z999AA10123456784",
            },
        )

        print(
            f"Multiple attributes updated successfully: {json.dumps(response.get('Attributes', {}), default=str)}"
        )
    except Exception as e:
        print(f"Error updating multiple attributes: {e}")

    print("\nExample 4: Conditional value copying with if_not_exists")
    try:
        response = update_with_conditional_value_copying(
            table_name=table_name,
            key={"OrderId": "order101"},
            source_attribute="PreferredShippingMethod",
            target_attribute="ShippingMethod",
            default_value="Standard",
        )

        print(
            f"Conditional value copying result: {json.dumps(response.get('Attributes', {}), default=str)}"
        )
    except Exception as e:
        print(f"Error with conditional value copying: {e}")

    print("\nKey Points About Update Expression Order of Operations:")
    print(
        "1. Variables in expressions hold copies of attribute values as they existed BEFORE any modifications"
    )
    print(
        "2. Multiple actions in an update expression are processed in this order: REMOVE, SET, ADD, DELETE"
    )
    print("3. Within each action type, operations are processed from left to right")
    print("4. You can reference the same attribute multiple times in an expression")
    print("5. You can use if_not_exists() to conditionally set values based on attribute existence")
    print(
        "6. Using a single update expression with multiple actions is more efficient than multiple separate updates"
    )
    print("7. The update expression is atomic - either all actions succeed or none do")
```
+  For API details, see [UpdateItem](https://docs.aws.amazon.com/goto/boto3/dynamodb-2012-08-10/UpdateItem) in *AWS SDK for Python (Boto3) API Reference*. 

------

For a complete list of AWS SDK developer guides and code examples, see [Using DynamoDB with an AWS SDK](sdk-general-information-section.md). This topic also includes information about getting started and details about previous SDK versions.