Weitere AWS SDK-Beispiele sind im GitHub Repo [AWS Doc SDK Examples](https://github.com/awsdocs/aws-doc-sdk-examples) verfügbar.

Die vorliegende Übersetzung wurde maschinell erstellt. Im Falle eines Konflikts oder eines Widerspruchs zwischen dieser übersetzten Fassung und der englischen Fassung (einschließlich infolge von Verzögerungen bei der Übersetzung) ist die englische Fassung maßgeblich.

# Verwenden Sie bedingte Operationen in DynamoDB mit einem SDK AWS
<a name="dynamodb_example_dynamodb_Scenario_ConditionalOperations_section"></a>

Die folgenden Codebeispiele zeigen, wie bedingte Operationen in DynamoDB verwendet werden.
+ Implementieren von bedingten Schreibvorgängen, um das Überschreiben von Daten zu verhindern
+ Verwenden von Bedingungsausdrücken, um Geschäftsregeln durchzusetzen
+ Ordnungsgemäßer Umgang mit Fehlern bei bedingten Prüfungen

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

**SDK für Java 2.x**  
Demonstrieren Sie bedingte Operationen mit 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.ConditionalCheckFailedException;
import software.amazon.awssdk.services.dynamodb.model.DeleteItemRequest;
import software.amazon.awssdk.services.dynamodb.model.DeleteItemResponse;
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;

    /**
     * Performs a conditional update on an item.
     *
     * <p>This method demonstrates how to use a condition expression to update an item
     * only if a specific condition is met.
     *
     * @param dynamoDbClient The DynamoDB client
     * @param tableName The name of the DynamoDB table
     * @param key The key of the item to update
     * @param conditionAttribute The attribute to check in the condition
     * @param conditionValue The value to compare against
     * @param updateAttribute The attribute to update
     * @param updateValue The new value to set
     * @return Map containing the operation result and status
     */
    public static Map<String, Object> conditionalUpdate(
        DynamoDbClient dynamoDbClient,
        String tableName,
        Map<String, AttributeValue> key,
        String conditionAttribute,
        AttributeValue conditionValue,
        String updateAttribute,
        AttributeValue updateValue) {

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

        try {
            // Define the update parameters
            UpdateItemRequest request = UpdateItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .updateExpression("SET #updateAttr = :updateVal")
                .conditionExpression("#condAttr = :condVal")
                .expressionAttributeNames(Map.of(
                    "#condAttr", conditionAttribute,
                    "#updateAttr", updateAttribute))
                .expressionAttributeValues(Map.of(
                    ":condVal", conditionValue,
                    ":updateVal", updateValue))
                .returnValues(ReturnValue.UPDATED_NEW)
                .build();

            // Perform the update operation
            UpdateItemResponse response = dynamoDbClient.updateItem(request);

            // Record success result
            result.put("success", true);
            result.put("message", "Condition was met and update was performed");
            result.put("attributes", response.attributes());

        } catch (ConditionalCheckFailedException e) {
            // Record failure due to condition not being met
            result.put("success", false);
            result.put("message", "Condition was not met, update was not performed");
            result.put("error", "ConditionalCheckFailedException");

        } catch (DynamoDbException e) {
            // Record failure due to other errors
            result.put("success", false);
            result.put("message", "Error occurred: " + e.getMessage());
            result.put("error", e.getClass().getSimpleName());
        }

        return result;
    }

    /**
     * Performs a conditional delete on an item.
     *
     * <p>This method demonstrates how to use a condition expression to delete an item
     * only if a specific condition is met.
     *
     * @param dynamoDbClient The DynamoDB client
     * @param tableName The name of the DynamoDB table
     * @param key The key of the item to delete
     * @param conditionAttribute The attribute to check in the condition
     * @param conditionValue The value to compare against
     * @return Map containing the operation result and status
     */
    public static Map<String, Object> conditionalDelete(
        DynamoDbClient dynamoDbClient,
        String tableName,
        Map<String, AttributeValue> key,
        String conditionAttribute,
        AttributeValue conditionValue) {

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

        try {
            // Define the delete parameters
            DeleteItemRequest request = DeleteItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .conditionExpression("#condAttr = :condVal")
                .expressionAttributeNames(Map.of("#condAttr", conditionAttribute))
                .expressionAttributeValues(Map.of(":condVal", conditionValue))
                .returnValues(ReturnValue.ALL_OLD)
                .build();

            // Perform the delete operation
            DeleteItemResponse response = dynamoDbClient.deleteItem(request);

            // Record success result
            result.put("success", true);
            result.put("message", "Condition was met and delete was performed");
            result.put("attributes", response.attributes());

        } catch (ConditionalCheckFailedException e) {
            // Record failure due to condition not being met
            result.put("success", false);
            result.put("message", "Condition was not met, delete was not performed");
            result.put("error", "ConditionalCheckFailedException");

        } catch (DynamoDbException e) {
            // Record failure due to other errors
            result.put("success", false);
            result.put("message", "Error occurred: " + e.getMessage());
            result.put("error", e.getClass().getSimpleName());
        }

        return result;
    }

    /**
     * Demonstrates optimistic locking using a version attribute.
     *
     * <p>This method shows how to implement optimistic locking by using a version
     * attribute that is incremented with each update.
     *
     * @param dynamoDbClient The DynamoDB client
     * @param tableName The name of the DynamoDB table
     * @param key The key of the item to update
     * @param versionAttribute The name of the version attribute
     * @return Map containing the operation result
     */
    public static Map<String, Object> optimisticLockingExample(
        DynamoDbClient dynamoDbClient, String tableName, Map<String, AttributeValue> key, String versionAttribute) {

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

        try {
            // Get the current version of the item
            GetItemRequest getRequest = GetItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .projectionExpression(versionAttribute)
                .build();

            GetItemResponse getResponse = dynamoDbClient.getItem(getRequest);

            // Check if the item exists
            if (getResponse.item() == null || !getResponse.item().containsKey(versionAttribute)) {
                // Item doesn't exist or doesn't have a version attribute
                // Initialize with version 1
                UpdateItemRequest initRequest = UpdateItemRequest.builder()
                    .tableName(tableName)
                    .key(key)
                    .updateExpression("SET #verAttr = :newVer, #dataAttr = :data")
                    .expressionAttributeNames(Map.of("#verAttr", versionAttribute, "#dataAttr", "Data"))
                    .expressionAttributeValues(Map.of(
                        ":newVer", AttributeValue.builder().n("1").build(),
                        ":data", AttributeValue.builder().s("Initial data").build()))
                    .returnValues(ReturnValue.UPDATED_NEW)
                    .build();

                UpdateItemResponse initResponse = dynamoDbClient.updateItem(initRequest);

                result.put("operation", "initialize");
                result.put("success", true);
                result.put("attributes", initResponse.attributes());

                return result;
            }

            // Get the current version number
            int currentVersion =
                Integer.parseInt(getResponse.item().get(versionAttribute).n());
            int newVersion = currentVersion + 1;

            // Update the item with a condition on the version
            UpdateItemRequest updateRequest = UpdateItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .updateExpression("SET #verAttr = :newVer, #dataAttr = :newData")
                .conditionExpression("#verAttr = :curVer")
                .expressionAttributeNames(Map.of("#verAttr", versionAttribute, "#dataAttr", "Data"))
                .expressionAttributeValues(Map.of(
                    ":curVer",
                        AttributeValue.builder()
                            .n(String.valueOf(currentVersion))
                            .build(),
                    ":newVer",
                        AttributeValue.builder().n(String.valueOf(newVersion)).build(),
                    ":newData",
                        AttributeValue.builder()
                            .s("Updated data at version " + newVersion)
                            .build()))
                .returnValues(ReturnValue.UPDATED_NEW)
                .build();

            UpdateItemResponse updateResponse = dynamoDbClient.updateItem(updateRequest);

            // Record success result
            result.put("operation", "update");
            result.put("success", true);
            result.put("oldVersion", currentVersion);
            result.put("newVersion", newVersion);
            result.put("attributes", updateResponse.attributes());

        } catch (ConditionalCheckFailedException e) {
            // Record failure due to version mismatch
            result.put("operation", "update");
            result.put("success", false);
            result.put("message", "Version mismatch, another process may have updated the item");
            result.put("error", "ConditionalCheckFailedException");

        } catch (DynamoDbException e) {
            // Record failure due to other errors
            result.put("operation", "update");
            result.put("success", false);
            result.put("message", "Error occurred: " + e.getMessage());
            result.put("error", e.getClass().getSimpleName());
        }

        return result;
    }

    /**
     * Performs a conditional update with multiple conditions.
     *
     * <p>This method demonstrates how to use multiple conditions in a condition expression.
     *
     * @param dynamoDbClient The DynamoDB client
     * @param tableName The name of the DynamoDB table
     * @param key The key of the item to update
     * @param conditions Map of attribute names to values for conditions
     * @param updateAttribute The attribute to update
     * @param updateValue The new value to set
     * @return Map containing the operation result and status
     */
    public static Map<String, Object> conditionalUpdateWithMultipleConditions(
        DynamoDbClient dynamoDbClient,
        String tableName,
        Map<String, AttributeValue> key,
        Map<String, AttributeValue> conditions,
        String updateAttribute,
        AttributeValue updateValue) {

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

        try {
            // Build the condition expression and attribute names/values
            StringBuilder conditionExpression = new StringBuilder();
            Map<String, String> expressionAttributeNames = new HashMap<>();
            Map<String, AttributeValue> expressionAttributeValues = new HashMap<>();

            // Add update attribute
            expressionAttributeNames.put("#updateAttr", updateAttribute);
            expressionAttributeValues.put(":updateVal", updateValue);

            // Add conditions
            int i = 0;
            for (Map.Entry<String, AttributeValue> condition : conditions.entrySet()) {
                String attrName = condition.getKey();
                AttributeValue attrValue = condition.getValue();

                String nameKey = "#cond" + i;
                String valueKey = ":val" + i;

                expressionAttributeNames.put(nameKey, attrName);
                expressionAttributeValues.put(valueKey, attrValue);

                // Add AND between conditions (except for the first one)
                if (i > 0) {
                    conditionExpression.append(" AND ");
                }

                conditionExpression.append(nameKey).append(" = ").append(valueKey);
                i++;
            }

            // Define the update parameters
            UpdateItemRequest request = UpdateItemRequest.builder()
                .tableName(tableName)
                .key(key)
                .updateExpression("SET #updateAttr = :updateVal")
                .conditionExpression(conditionExpression.toString())
                .expressionAttributeNames(expressionAttributeNames)
                .expressionAttributeValues(expressionAttributeValues)
                .returnValues(ReturnValue.UPDATED_NEW)
                .build();

            // Perform the update operation
            UpdateItemResponse response = dynamoDbClient.updateItem(request);

            // Record success result
            result.put("success", true);
            result.put("message", "All conditions were met and update was performed");
            result.put("attributes", response.attributes());

        } catch (ConditionalCheckFailedException e) {
            // Record failure due to condition not being met
            result.put("success", false);
            result.put("message", "One or more conditions were not met, update was not performed");
            result.put("error", "ConditionalCheckFailedException");

        } catch (DynamoDbException e) {
            // Record failure due to other errors
            result.put("success", false);
            result.put("message", "Error occurred: " + e.getMessage());
            result.put("error", e.getClass().getSimpleName());
        }

        return result;
    }
```
Beispiel für die Verwendung von bedingten Operationen mit 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 conditional operations in DynamoDB");

        try {
            // Example 1: Conditional update
            System.out.println("\nExample 1: Conditional update");
            Map<String, Object> updateResult = conditionalUpdate(
                dynamoDbClient,
                tableName,
                key,
                "InStock",
                AttributeValue.builder().bool(true).build(),
                "Status",
                AttributeValue.builder().s("Available").build());

            System.out.println("Update result: " + updateResult.get("message"));
            if ((boolean) updateResult.get("success")) {
                System.out.println("Updated attributes: " + updateResult.get("attributes"));
            }

            // Example 2: Conditional delete
            System.out.println("\nExample 2: Conditional delete");
            Map<String, Object> deleteResult = conditionalDelete(
                dynamoDbClient,
                tableName,
                key,
                "Status",
                AttributeValue.builder().s("Discontinued").build());

            System.out.println("Delete result: " + deleteResult.get("message"));
            if ((boolean) deleteResult.get("success")) {
                System.out.println("Deleted item: " + deleteResult.get("attributes"));
            }

            // Example 3: Optimistic locking
            System.out.println("\nExample 3: Optimistic locking");
            Map<String, Object> lockingResult = optimisticLockingExample(dynamoDbClient, tableName, key, "Version");

            System.out.println("Optimistic locking result:");
            System.out.println("  Operation: " + lockingResult.get("operation"));
            System.out.println("  Success: " + lockingResult.get("success"));
            if (lockingResult.get("operation").equals("update") && (boolean) lockingResult.get("success")) {
                System.out.println("  Old version: " + lockingResult.get("oldVersion"));
                System.out.println("  New version: " + lockingResult.get("newVersion"));
            }
            System.out.println("  Attributes: " + lockingResult.get("attributes"));

            // Example 4: Multiple conditions
            System.out.println("\nExample 4: Multiple conditions");
            Map<String, AttributeValue> conditions = new HashMap<>();
            conditions.put("Price", AttributeValue.builder().n("199.99").build());
            conditions.put("Category", AttributeValue.builder().s("Electronics").build());

            Map<String, Object> multiConditionResult = conditionalUpdateWithMultipleConditions(
                dynamoDbClient,
                tableName,
                key,
                conditions,
                "OnSale",
                AttributeValue.builder().bool(true).build());

            System.out.println("Multiple conditions result: " + multiConditionResult.get("message"));
            if ((boolean) multiConditionResult.get("success")) {
                System.out.println("Updated attributes: " + multiConditionResult.get("attributes"));
            }

            // Explain conditional operations
            System.out.println("\nKey points about DynamoDB conditional operations:");
            System.out.println("1. Conditional operations only succeed if the condition is met");
            System.out.println("2. ConditionalCheckFailedException is thrown when the condition fails");
            System.out.println("3. No changes are made to the item if the condition fails");
            System.out.println("4. Conditions can be used with update, delete, and put operations");
            System.out.println("5. Multiple conditions can be combined with AND and OR");
            System.out.println("6. Optimistic locking can be implemented using a version attribute");
            System.out.println(
                "7. Conditional operations consume the same amount of write capacity whether they succeed or fail");

        } catch (DynamoDbException e) {
            System.err.println("Error: " + e.getMessage());
            e.printStackTrace();
        }
    }
```
+ Weitere API-Informationen finden Sie in den folgenden Themen der *AWS SDK for Java 2.x -API-Referenz*.
  + [DeleteItem](https://docs.aws.amazon.com/goto/SdkForJavaV2/dynamodb-2012-08-10/DeleteItem)
  + [PutItem](https://docs.aws.amazon.com/goto/SdkForJavaV2/dynamodb-2012-08-10/PutItem)
  + [UpdateItem](https://docs.aws.amazon.com/goto/SdkForJavaV2/dynamodb-2012-08-10/UpdateItem)

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

**SDK für JavaScript (v3)**  
Demonstrieren Sie bedingte Operationen mit AWS SDK für JavaScript.  

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

/**
 * Perform a conditional update operation.
 * 
 * This function demonstrates how to update an item only if a condition is met.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {string} conditionAttribute - The attribute to check in the condition
 * @param {any} conditionValue - The value to compare against
 * @param {string} updateAttribute - The attribute to update
 * @param {any} updateValue - The new value to set
 * @returns {Promise<Object>} - Result of the operation
 */
async function conditionalUpdate(
  config,
  tableName,
  key,
  conditionAttribute,
  conditionValue,
  updateAttribute,
  updateValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the update parameters with a condition expression
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${updateAttribute} = :value`,
    ConditionExpression: `${conditionAttribute} = :condition`,
    ExpressionAttributeValues: {
      ":value": updateValue,
      ":condition": conditionValue
    },
    ReturnValues: "UPDATED_NEW"
  };
  
  try {
    // Perform the update operation
    const response = await docClient.send(new UpdateCommand(params));
    
    return {
      success: true,
      message: "Condition was met and update was performed",
      updatedAttributes: response.Attributes
    };
  } catch (error) {
    // Check if the error is due to the condition check failing
    if (error.name === "ConditionalCheckFailedException") {
      return {
        success: false,
        message: "Condition was not met, update was not performed",
        error: "ConditionalCheckFailedException"
      };
    }
    
    // Re-throw other errors
    throw error;
  }
}

/**
 * Perform a conditional delete operation.
 * 
 * This function demonstrates how to delete an item only if a condition is met.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to delete
 * @param {string} conditionAttribute - The attribute to check in the condition
 * @param {any} conditionValue - The value to compare against
 * @returns {Promise<Object>} - Result of the operation
 */
async function conditionalDelete(
  config,
  tableName,
  key,
  conditionAttribute,
  conditionValue
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the delete parameters with a condition expression
  const params = {
    TableName: tableName,
    Key: key,
    ConditionExpression: `${conditionAttribute} = :condition`,
    ExpressionAttributeValues: {
      ":condition": conditionValue
    },
    ReturnValues: "ALL_OLD"
  };
  
  try {
    // Perform the delete operation
    const response = await docClient.send(new DeleteCommand(params));
    
    return {
      success: true,
      message: "Condition was met and item was deleted",
      deletedItem: response.Attributes
    };
  } catch (error) {
    // Check if the error is due to the condition check failing
    if (error.name === "ConditionalCheckFailedException") {
      return {
        success: false,
        message: "Condition was not met, item was not deleted",
        error: "ConditionalCheckFailedException"
      };
    }
    
    // Re-throw other errors
    throw error;
  }
}

/**
 * Implement optimistic locking with a version number.
 * 
 * This function demonstrates how to use a version number for optimistic locking
 * to prevent race conditions when multiple processes update the same item.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to update
 * @param {Object} updates - The attributes to update
 * @param {number} expectedVersion - The expected current version number
 * @returns {Promise<Object>} - Result of the operation
 */
async function updateWithOptimisticLocking(
  config,
  tableName,
  key,
  updates,
  expectedVersion
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Build the update expression
  const updateExpressions = [];
  const expressionAttributeValues = {
    ":expectedVersion": expectedVersion,
    ":newVersion": expectedVersion + 1
  };
  
  // Add each update to the expression
  Object.entries(updates).forEach(([attribute, value], index) => {
    updateExpressions.push(`${attribute} = :val${index}`);
    expressionAttributeValues[`:val${index}`] = value;
  });
  
  // Add the version update
  updateExpressions.push("version = :newVersion");
  
  // Define the update parameters with a condition expression
  const params = {
    TableName: tableName,
    Key: key,
    UpdateExpression: `SET ${updateExpressions.join(", ")}`,
    ConditionExpression: "version = :expectedVersion",
    ExpressionAttributeValues: expressionAttributeValues,
    ReturnValues: "UPDATED_NEW"
  };
  
  try {
    // Perform the update operation
    const response = await docClient.send(new UpdateCommand(params));
    
    return {
      success: true,
      message: "Update succeeded with optimistic locking",
      newVersion: expectedVersion + 1,
      updatedAttributes: response.Attributes
    };
  } catch (error) {
    // Check if the error is due to the condition check failing
    if (error.name === "ConditionalCheckFailedException") {
      return {
        success: false,
        message: "Optimistic locking failed: the item was modified by another process",
        error: "ConditionalCheckFailedException"
      };
    }
    
    // Re-throw other errors
    throw error;
  }
}

/**
 * Implement a conditional write that creates an item only if it doesn't exist.
 * 
 * This function demonstrates how to use attribute_not_exists to create an item
 * only if it doesn't already exist (similar to an "INSERT IF NOT EXISTS" operation).
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} item - The item to create
 * @returns {Promise<Object>} - Result of the operation
 */
async function createIfNotExists(
  config,
  tableName,
  item
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Extract the primary key attributes
  const keyAttributes = Object.keys(item).filter(attr => 
    attr === "id" || attr === "ID" || attr === "Id" || 
    attr.endsWith("Id") || attr.endsWith("ID") || 
    attr.endsWith("Key")
  );
  
  if (keyAttributes.length === 0) {
    throw new Error("Could not determine primary key attributes");
  }
  
  // Create a condition expression that checks if the item doesn't exist
  const conditionExpression = `attribute_not_exists(${keyAttributes[0]})`;
  
  // Define the put parameters with a condition expression
  const params = {
    TableName: tableName,
    Item: item,
    ConditionExpression: conditionExpression
  };
  
  try {
    // Perform the put operation
    await docClient.send(new PutCommand(params));
    
    return {
      success: true,
      message: "Item was created because it didn't exist",
      item
    };
  } catch (error) {
    // Check if the error is due to the condition check failing
    if (error.name === "ConditionalCheckFailedException") {
      return {
        success: false,
        message: "Item already exists, creation was skipped",
        error: "ConditionalCheckFailedException"
      };
    }
    
    // Re-throw other errors
    throw error;
  }
}

/**
 * Get the current value of an item.
 * 
 * Helper function to retrieve the current value of an item.
 * 
 * @param {Object} config - AWS configuration object
 * @param {string} tableName - The name of the DynamoDB table
 * @param {Object} key - The key of the item to get
 * @returns {Promise<Object|null>} - The item or null if not found
 */
async function getItem(
  config,
  tableName,
  key
) {
  // Initialize the DynamoDB client
  const client = new DynamoDBClient(config);
  const docClient = DynamoDBDocumentClient.from(client);
  
  // Define the get parameters
  const params = {
    TableName: tableName,
    Key: key
  };
  
  // Perform the get operation
  const response = await docClient.send(new GetCommand(params));
  
  // Return the item if it exists, otherwise null
  return response.Item || null;
}
```
Beispiel für die Verwendung von bedingten Operationen mit AWS SDK für JavaScript.  

```
/**
 * Example of how to use conditional operations.
 */
async function exampleUsage() {
  // Example parameters
  const config = { region: "us-west-2" };
  const tableName = "Products";
  const key = { ProductId: "P12345" };
  
  console.log("Demonstrating conditional operations in DynamoDB");
  
  try {
    // Example 1: Conditional update based on attribute value
    console.log("\nExample 1: Conditional update based on attribute value");
    const updateResult = await conditionalUpdate(
      config,
      tableName,
      key,
      "Category",
      "Electronics",
      "Price",
      299.99
    );
    
    console.log(`Result: ${updateResult.message}`);
    if (updateResult.success) {
      console.log("Updated attributes:", updateResult.updatedAttributes);
    }
    
    // Example 2: Conditional delete based on attribute value
    console.log("\nExample 2: Conditional delete based on attribute value");
    const deleteResult = await conditionalDelete(
      config,
      tableName,
      key,
      "InStock",
      false
    );
    
    console.log(`Result: ${deleteResult.message}`);
    if (deleteResult.success) {
      console.log("Deleted item:", deleteResult.deletedItem);
    }
    
    // Example 3: Optimistic locking with version number
    console.log("\nExample 3: Optimistic locking with version number");
    
    // First, get the current item to check its version
    const currentItem = await getItem(config, tableName, { ProductId: "P67890" });
    const currentVersion = currentItem ? (currentItem.version || 0) : 0;
    
    console.log(`Current version: ${currentVersion}`);
    
    // Then, update with optimistic locking
    const lockingResult = await updateWithOptimisticLocking(
      config,
      tableName,
      { ProductId: "P67890" },
      {
        Name: "Updated Product Name",
        Description: "This is an updated description"
      },
      currentVersion
    );
    
    console.log(`Result: ${lockingResult.message}`);
    if (lockingResult.success) {
      console.log(`New version: ${lockingResult.newVersion}`);
      console.log("Updated attributes:", lockingResult.updatedAttributes);
    }
    
    // Example 4: Create item only if it doesn't exist
    console.log("\nExample 4: Create item only if it doesn't exist");
    const createResult = await createIfNotExists(
      config,
      tableName,
      {
        ProductId: "P99999",
        Name: "New Product",
        Category: "Accessories",
        Price: 19.99,
        InStock: true
      }
    );
    
    console.log(`Result: ${createResult.message}`);
    if (createResult.success) {
      console.log("Created item:", createResult.item);
    }
    
    // Explain conditional operations
    console.log("\nKey points about conditional operations:");
    console.log("1. Conditional operations only succeed if the condition is met");
    console.log("2. ConditionalCheckFailedException indicates the condition wasn't met");
    console.log("3. Optimistic locking prevents race conditions in concurrent updates");
    console.log("4. attribute_exists and attribute_not_exists are useful for checking if attributes are present");
    console.log("5. Conditional operations are atomic - they either succeed completely or fail completely");
    console.log("6. You can use any valid comparison operators and functions in condition expressions");
    console.log("7. Conditional operations don't consume write capacity if the condition fails");
    
  } catch (error) {
    console.error("Error:", error);
  }
}
```
+ Weitere API-Informationen finden Sie in den folgenden Themen der *AWS SDK für JavaScript -API-Referenz*.
  + [DeleteItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/DeleteItemCommand)
  + [PutItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/PutItemCommand)
  + [UpdateItem](https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/dynamodb/command/UpdateItemCommand)

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

**SDK für Python (Boto3)**  
Demonstrieren Sie bedingte Operationen mit AWS SDK für Python (Boto3).  

```
import boto3
from botocore.exceptions import ClientError
from typing import Any, Dict, Optional, Tuple, Union


def conditional_update(
    table_name: str,
    key: Dict[str, Any],
    condition_attribute: str,
    condition_value: Any,
    update_attribute: str,
    update_value: Any,
) -> Tuple[bool, Optional[Dict[str, Any]]]:
    """
    Update an item only if a condition is met.

    This function demonstrates how to perform a conditional update operation
    and determine if the condition was met.

    Args:
        table_name (str): The name of the DynamoDB table.
        key (Dict[str, Any]): The primary key of the item to update.
        condition_attribute (str): The attribute to check in the condition.
        condition_value (Any): The value to compare against.
        update_attribute (str): The attribute to update.
        update_value (Any): The new value to set.

    Returns:
        Tuple[bool, Optional[Dict[str, Any]]]: A tuple containing:
            - A boolean indicating if the update succeeded
            - The response from DynamoDB if successful, None otherwise
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    try:
        # Perform the conditional update
        response = table.update_item(
            Key=key,
            UpdateExpression="SET #update_attr = :update_val",
            ConditionExpression="#cond_attr = :cond_val",
            ExpressionAttributeNames={
                "#update_attr": update_attribute,
                "#cond_attr": condition_attribute,
            },
            ExpressionAttributeValues={":update_val": update_value, ":cond_val": condition_value},
            ReturnValues="UPDATED_NEW",
        )
        # Update succeeded, condition was met
        return True, response
    except ClientError as e:
        if e.response["Error"]["Code"] == "ConditionalCheckFailedException":
            # Condition was not met
            return False, None
        else:
            # Other error occurred
            raise


def conditional_delete(
    table_name: str, key: Dict[str, Any], condition_attribute: str, condition_value: Any
) -> bool:
    """
    Delete an item only if a condition is met.

    This function demonstrates how to perform a conditional delete operation
    and determine if the condition was met.

    Args:
        table_name (str): The name of the DynamoDB table.
        key (Dict[str, Any]): The primary key of the item to delete.
        condition_attribute (str): The attribute to check in the condition.
        condition_value (Any): The value to compare against.

    Returns:
        bool: True if the delete succeeded (condition was met), False otherwise.
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    try:
        # Perform the conditional delete
        table.delete_item(
            Key=key,
            ConditionExpression="#attr = :val",
            ExpressionAttributeNames={"#attr": condition_attribute},
            ExpressionAttributeValues={":val": condition_value},
        )
        # Delete succeeded, condition was met
        return True
    except ClientError as e:
        if e.response["Error"]["Code"] == "ConditionalCheckFailedException":
            # Condition was not met
            return False
        else:
            # Other error occurred
            raise


def optimistic_locking_update(
    table_name: str,
    key: Dict[str, Any],
    version_attribute: str,
    update_attribute: str,
    update_value: Any,
) -> Tuple[bool, Optional[Dict[str, Any]]]:
    """
    Update an item using optimistic locking with a version attribute.

    This function demonstrates how to implement optimistic locking using
    a version attribute that is incremented with each update.

    Args:
        table_name (str): The name of the DynamoDB table.
        key (Dict[str, Any]): The primary key of the item to update.
        version_attribute (str): The name of the version attribute.
        update_attribute (str): The attribute to update.
        update_value (Any): The new value to set.

    Returns:
        Tuple[bool, Optional[Dict[str, Any]]]: A tuple containing:
            - A boolean indicating if the update succeeded
            - The response from DynamoDB if successful, None otherwise
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    # First, get the current version
    try:
        response = table.get_item(
            Key=key,
            ProjectionExpression=f"#{version_attribute}",
            ExpressionAttributeNames={f"#{version_attribute}": version_attribute},
        )

        item = response.get("Item", {})
        current_version = item.get(version_attribute, 0)

        # Now, try to update with a condition on the version
        try:
            update_response = table.update_item(
                Key=key,
                UpdateExpression=f"SET #{update_attribute} = :update_val, #{version_attribute} = :new_version",
                ConditionExpression=f"#{version_attribute} = :current_version",
                ExpressionAttributeNames={
                    f"#{update_attribute}": update_attribute,
                    f"#{version_attribute}": version_attribute,
                },
                ExpressionAttributeValues={
                    ":update_val": update_value,
                    ":current_version": current_version,
                    ":new_version": current_version + 1,
                },
                ReturnValues="UPDATED_NEW",
            )
            # Update succeeded
            return True, update_response
        except ClientError as e:
            if e.response["Error"]["Code"] == "ConditionalCheckFailedException":
                # Version has changed, optimistic locking failed
                return False, None
            else:
                # Other error occurred
                raise
    except ClientError:
        # Error getting the item
        raise


def conditional_check_and_update(
    table_name: str,
    key: Dict[str, Any],
    check_attribute: str,
    check_value: Any,
    update_attribute: str,
    update_value: Any,
    create_if_not_exists: bool = False,
) -> Union[Dict[str, Any], None]:
    """
    Check if an attribute has a specific value and update another attribute if it does.

    This function demonstrates a more complex conditional update that can also
    create the item if it 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.
        check_attribute (str): The attribute to check in the condition.
        check_value (Any): The value to compare against.
        update_attribute (str): The attribute to update.
        update_value (Any): The new value to set.
        create_if_not_exists (bool, optional): Whether to create the item if it doesn't exist.

    Returns:
        Union[Dict[str, Any], None]: The response from DynamoDB if successful, None otherwise.
    """
    # Initialize the DynamoDB resource
    dynamodb = boto3.resource("dynamodb")
    table = dynamodb.Table(table_name)

    try:
        if create_if_not_exists:
            # Use attribute_not_exists to create the item if it doesn't exist
            condition_expression = "attribute_not_exists(#pk) OR #check_attr = :check_val"
            update_expression = "SET #update_attr = :update_val, #check_attr = if_not_exists(#check_attr, :check_val)"

            # Get the partition key name from the key dictionary
            pk_name = next(iter(key))

            expression_attribute_names = {
                "#pk": pk_name,
                "#check_attr": check_attribute,
                "#update_attr": update_attribute,
            }
        else:
            # Only update if the check attribute has the expected value
            condition_expression = "#check_attr = :check_val"
            update_expression = "SET #update_attr = :update_val"

            expression_attribute_names = {
                "#check_attr": check_attribute,
                "#update_attr": update_attribute,
            }

        # Perform the conditional update
        response = table.update_item(
            Key=key,
            UpdateExpression=update_expression,
            ConditionExpression=condition_expression,
            ExpressionAttributeNames=expression_attribute_names,
            ExpressionAttributeValues={":check_val": check_value, ":update_val": update_value},
            ReturnValues="UPDATED_NEW",
        )
        return response
    except ClientError as e:
        if e.response["Error"]["Code"] == "ConditionalCheckFailedException":
            # Condition was not met
            return None
        else:
            # Other error occurred
            raise
```
Beispiel für die Verwendung von bedingten Operationen mit AWS SDK für Python (Boto3).  

```
def example_usage():
    """Example of how to use the conditional operations functions."""
    # Example parameters
    table_name = "Products"
    key = {"ProductId": "prod123"}

    print("Example 1: Conditional Update")
    try:
        # Update the price only if the current stock is greater than 10
        success, response = conditional_update(
            table_name=table_name,
            key=key,
            condition_attribute="Stock",
            condition_value=10,
            update_attribute="Price",
            update_value=99.99,
        )

        if success:
            # Fix for mypy: Handle the case where response might be None
            attributes = {} if response is None else response.get("Attributes", {})
            print(f"Update succeeded! New values: {attributes}")
        else:
            print("Update failed because the condition was not met.")
    except Exception as e:
        print(f"Error during conditional update: {e}")

    print("\nExample 2: Conditional Delete")
    try:
        # Delete the product only if it's discontinued
        success = conditional_delete(
            table_name=table_name,
            key=key,
            condition_attribute="Status",
            condition_value="Discontinued",
        )

        if success:
            print("Delete succeeded! The item was deleted.")
        else:
            print("Delete failed because the condition was not met.")
    except Exception as e:
        print(f"Error during conditional delete: {e}")

    print("\nExample 3: Optimistic Locking")
    try:
        # Update with optimistic locking using a version attribute
        success, response = optimistic_locking_update(
            table_name=table_name,
            key=key,
            version_attribute="Version",
            update_attribute="Description",
            update_value="Updated product description",
        )

        if success:
            # Fix for mypy: Handle the case where response might be None
            attributes = {} if response is None else response.get("Attributes", {})
            print(f"Optimistic locking update succeeded! New values: {attributes}")
        else:
            print("Optimistic locking update failed because the version has changed.")
    except Exception as e:
        print(f"Error during optimistic locking update: {e}")

    print("\nExample 4: Conditional Check and Update")
    try:
        # Update the featured status if the product is in stock
        response = conditional_check_and_update(
            table_name=table_name,
            key=key,
            check_attribute="InStock",
            check_value=True,
            update_attribute="Featured",
            update_value=True,
            create_if_not_exists=True,
        )

        if response:
            print(
                f"Conditional check and update succeeded! New values: {response.get('Attributes', {})}"
            )
        else:
            print("Conditional check and update failed because the condition was not met.")
    except Exception as e:
        print(f"Error during conditional check and update: {e}")

    print("\nUnderstanding Conditional Operations in DynamoDB:")
    print("1. Conditional operations help maintain data integrity")
    print("2. They prevent race conditions in concurrent environments")
    print("3. Failed conditions result in ConditionalCheckFailedException")
    print("4. No DynamoDB capacity is consumed when conditions fail")
    print("5. Optimistic locking is a common pattern using version attributes")
    print("6. Conditions can be combined with logical operators (AND, OR, NOT)")
    print("7. Conditions can use comparison operators (=, <>, <, <=, >, >=)")
    print(
        "8. attribute_exists() and attribute_not_exists() are useful for checking attribute presence"
    )
```
+ Weitere API-Informationen finden Sie in den folgenden Themen der *API-Referenz zum AWS SDK für Python (Boto3)*.
  + [DeleteItem](https://docs.aws.amazon.com/goto/boto3/dynamodb-2012-08-10/DeleteItem)
  + [PutItem](https://docs.aws.amazon.com/goto/boto3/dynamodb-2012-08-10/PutItem)
  + [UpdateItem](https://docs.aws.amazon.com/goto/boto3/dynamodb-2012-08-10/UpdateItem)

------