DynamoDBMapper Transaction operations

The following Java code example declares a Forum and a Thread class and maps them to the DynamoDB tables using the DynamoDBMapper class.

The code illustrates the following transactional operations:

Imports

import java.util.ArrayList;
import java.util.List;
import java.util.Set;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBHashKey;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMappingException;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBRangeKey;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTransactionLoadExpression;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTransactionWriteExpression;
import com.amazonaws.services.dynamodbv2.datamodeling.TransactionLoadRequest;
import com.amazonaws.services.dynamodbv2.datamodeling.TransactionWriteRequest;
import com.amazonaws.services.dynamodbv2.model.InternalServerErrorException;
import com.amazonaws.services.dynamodbv2.model.ResourceNotFoundException;
import com.amazonaws.services.dynamodbv2.model.TransactionCanceledException;

Code

public class DynamoDBMapperTransactionExample {

    static AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();
    static DynamoDBMapper mapper;

    public static void main(String[] args) throws Exception {
        try {

            mapper = new DynamoDBMapper(client);

            testPutAndUpdateInTransactionWrite();
            testPutWithConditionalUpdateInTransactionWrite();
            testPutWithConditionCheckInTransactionWrite();
            testMixedOperationsInTransactionWrite();
            testTransactionLoadWithSave();
            testTransactionLoadWithTransactionWrite();
            System.out.println("Example complete");

        } catch (Throwable t) {
            System.err.println("Error running the DynamoDBMapperTransactionWriteExample: " + t);
            t.printStackTrace();
        }
    }

    private static void testTransactionLoadWithSave() {
        // Create new Forum item for DynamoDB using save
        Forum dynamodbForum = new Forum();
        dynamodbForum.setName("DynamoDB Forum");
        dynamodbForum.setCategory("Amazon Web Services");
        dynamodbForum.setThreads(0);
        mapper.save(dynamodbForum);

        // Add a thread to DynamoDB Forum
        Thread dynamodbForumThread = new Thread();
        dynamodbForumThread.setForumName("DynamoDB Forum");
        dynamodbForumThread.setSubject("Sample Subject 1");
        dynamodbForumThread.setMessage("Sample Question 1");
        mapper.save(dynamodbForumThread);

        // Update DynamoDB Forum to reflect updated thread count
        dynamodbForum.setThreads(1);
        mapper.save(dynamodbForum);

        // Read DynamoDB Forum item and Thread item at the same time in a serializable
        // manner
        TransactionLoadRequest transactionLoadRequest = new TransactionLoadRequest();

        // Read entire item for DynamoDB Forum
        transactionLoadRequest.addLoad(dynamodbForum);

        // Only read subject and message attributes from Thread item
        DynamoDBTransactionLoadExpression loadExpressionForThread = new DynamoDBTransactionLoadExpression()
                .withProjectionExpression("Subject, Message");
        transactionLoadRequest.addLoad(dynamodbForumThread, loadExpressionForThread);

        // Loaded objects are guaranteed to be in same order as the order in which they
        // are
        // added to TransactionLoadRequest
        List<Object> loadedObjects = executeTransactionLoad(transactionLoadRequest);
        Forum loadedDynamoDBForum = (Forum) loadedObjects.get(0);
        System.out.println("Forum: " + loadedDynamoDBForum.getName());
        System.out.println("Threads: " + loadedDynamoDBForum.getThreads());
        Thread loadedDynamodbForumThread = (Thread) loadedObjects.get(1);
        System.out.println("Subject: " + loadedDynamodbForumThread.getSubject());
        System.out.println("Message: " + loadedDynamodbForumThread.getMessage());
    }

    private static void testTransactionLoadWithTransactionWrite() {
        // Create new Forum item for DynamoDB using save
        Forum dynamodbForum = new Forum();
        dynamodbForum.setName("DynamoDB New Forum");
        dynamodbForum.setCategory("Amazon Web Services");
        dynamodbForum.setThreads(0);
        mapper.save(dynamodbForum);

        // Update Forum item for DynamoDB and add a thread to DynamoDB Forum, in
        // an ACID manner using transactionWrite

        dynamodbForum.setThreads(1);
        Thread dynamodbForumThread = new Thread();
        dynamodbForumThread.setForumName("DynamoDB New Forum");
        dynamodbForumThread.setSubject("Sample Subject 2");
        dynamodbForumThread.setMessage("Sample Question 2");
        TransactionWriteRequest transactionWriteRequest = new TransactionWriteRequest();
        transactionWriteRequest.addPut(dynamodbForumThread);
        transactionWriteRequest.addUpdate(dynamodbForum);
        executeTransactionWrite(transactionWriteRequest);

        // Read DynamoDB Forum item and Thread item at the same time in a serializable
        // manner
        TransactionLoadRequest transactionLoadRequest = new TransactionLoadRequest();

        // Read entire item for DynamoDB Forum
        transactionLoadRequest.addLoad(dynamodbForum);

        // Only read subject and message attributes from Thread item
        DynamoDBTransactionLoadExpression loadExpressionForThread = new DynamoDBTransactionLoadExpression()
                .withProjectionExpression("Subject, Message");
        transactionLoadRequest.addLoad(dynamodbForumThread, loadExpressionForThread);

        // Loaded objects are guaranteed to be in same order as the order in which they
        // are
        // added to TransactionLoadRequest
        List<Object> loadedObjects = executeTransactionLoad(transactionLoadRequest);
        Forum loadedDynamoDBForum = (Forum) loadedObjects.get(0);
        System.out.println("Forum: " + loadedDynamoDBForum.getName());
        System.out.println("Threads: " + loadedDynamoDBForum.getThreads());
        Thread loadedDynamodbForumThread = (Thread) loadedObjects.get(1);
        System.out.println("Subject: " + loadedDynamodbForumThread.getSubject());
        System.out.println("Message: " + loadedDynamodbForumThread.getMessage());
    }

    private static void testPutAndUpdateInTransactionWrite() {
        // Create new Forum item for S3 using save
        Forum s3Forum = new Forum();
        s3Forum.setName("S3 Forum");
        s3Forum.setCategory("Core Amazon Web Services");
        s3Forum.setThreads(0);
        mapper.save(s3Forum);

        // Update Forum item for S3 and Create new Forum item for DynamoDB using
        // transactionWrite
        s3Forum.setCategory("Amazon Web Services");
        Forum dynamodbForum = new Forum();
        dynamodbForum.setName("DynamoDB Forum");
        dynamodbForum.setCategory("Amazon Web Services");
        dynamodbForum.setThreads(0);
        TransactionWriteRequest transactionWriteRequest = new TransactionWriteRequest();
        transactionWriteRequest.addUpdate(s3Forum);
        transactionWriteRequest.addPut(dynamodbForum);
        executeTransactionWrite(transactionWriteRequest);
    }

    private static void testPutWithConditionalUpdateInTransactionWrite() {
        // Create new Thread item for DynamoDB forum and update thread count in DynamoDB
        // forum
        // if the DynamoDB Forum exists
        Thread dynamodbForumThread = new Thread();
        dynamodbForumThread.setForumName("DynamoDB Forum");
        dynamodbForumThread.setSubject("Sample Subject 1");
        dynamodbForumThread.setMessage("Sample Question 1");

        Forum dynamodbForum = new Forum();
        dynamodbForum.setName("DynamoDB Forum");
        dynamodbForum.setCategory("Amazon Web Services");
        dynamodbForum.setThreads(1);

        DynamoDBTransactionWriteExpression transactionWriteExpression = new DynamoDBTransactionWriteExpression()
                .withConditionExpression("attribute_exists(Category)");

        TransactionWriteRequest transactionWriteRequest = new TransactionWriteRequest();
        transactionWriteRequest.addPut(dynamodbForumThread);
        transactionWriteRequest.addUpdate(dynamodbForum, transactionWriteExpression);
        executeTransactionWrite(transactionWriteRequest);
    }

    private static void testPutWithConditionCheckInTransactionWrite() {
        // Create new Thread item for DynamoDB forum and update thread count in DynamoDB
        // forum if a thread already exists
        Thread dynamodbForumThread2 = new Thread();
        dynamodbForumThread2.setForumName("DynamoDB Forum");
        dynamodbForumThread2.setSubject("Sample Subject 2");
        dynamodbForumThread2.setMessage("Sample Question 2");

        Thread dynamodbForumThread1 = new Thread();
        dynamodbForumThread1.setForumName("DynamoDB Forum");
        dynamodbForumThread1.setSubject("Sample Subject 1");
        DynamoDBTransactionWriteExpression conditionExpressionForConditionCheck = new DynamoDBTransactionWriteExpression()
                .withConditionExpression("attribute_exists(Subject)");

        Forum dynamodbForum = new Forum();
        dynamodbForum.setName("DynamoDB Forum");
        dynamodbForum.setCategory("Amazon Web Services");
        dynamodbForum.setThreads(2);

        TransactionWriteRequest transactionWriteRequest = new TransactionWriteRequest();
        transactionWriteRequest.addPut(dynamodbForumThread2);
        transactionWriteRequest.addConditionCheck(dynamodbForumThread1, conditionExpressionForConditionCheck);
        transactionWriteRequest.addUpdate(dynamodbForum);
        executeTransactionWrite(transactionWriteRequest);
    }

    private static void testMixedOperationsInTransactionWrite() {
        // Create new Thread item for S3 forum and delete "Sample Subject 1" Thread from
        // DynamoDB forum if
        // "Sample Subject 2" Thread exists in DynamoDB forum
        Thread s3ForumThread = new Thread();
        s3ForumThread.setForumName("S3 Forum");
        s3ForumThread.setSubject("Sample Subject 1");
        s3ForumThread.setMessage("Sample Question 1");

        Forum s3Forum = new Forum();
        s3Forum.setName("S3 Forum");
        s3Forum.setCategory("Amazon Web Services");
        s3Forum.setThreads(1);

        Thread dynamodbForumThread1 = new Thread();
        dynamodbForumThread1.setForumName("DynamoDB Forum");
        dynamodbForumThread1.setSubject("Sample Subject 1");

        Thread dynamodbForumThread2 = new Thread();
        dynamodbForumThread2.setForumName("DynamoDB Forum");
        dynamodbForumThread2.setSubject("Sample Subject 2");
        DynamoDBTransactionWriteExpression conditionExpressionForConditionCheck = new DynamoDBTransactionWriteExpression()
                .withConditionExpression("attribute_exists(Subject)");

        Forum dynamodbForum = new Forum();
        dynamodbForum.setName("DynamoDB Forum");
        dynamodbForum.setCategory("Amazon Web Services");
        dynamodbForum.setThreads(1);

        TransactionWriteRequest transactionWriteRequest = new TransactionWriteRequest();
        transactionWriteRequest.addPut(s3ForumThread);
        transactionWriteRequest.addUpdate(s3Forum);
        transactionWriteRequest.addDelete(dynamodbForumThread1);
        transactionWriteRequest.addConditionCheck(dynamodbForumThread2, conditionExpressionForConditionCheck);
        transactionWriteRequest.addUpdate(dynamodbForum);
        executeTransactionWrite(transactionWriteRequest);
    }

    private static List<Object> executeTransactionLoad(TransactionLoadRequest transactionLoadRequest) {
        List<Object> loadedObjects = new ArrayList<Object>();
        try {
            loadedObjects = mapper.transactionLoad(transactionLoadRequest);
        } catch (DynamoDBMappingException ddbme) {
            System.err.println("Client side error in Mapper, fix before retrying. Error: " + ddbme.getMessage());
        } catch (ResourceNotFoundException rnfe) {
            System.err.println("One of the tables was not found, verify table exists before retrying. Error: "
                    + rnfe.getMessage());
        } catch (InternalServerErrorException ise) {
            System.err.println(
                    "Internal Server Error, generally safe to retry with back-off. Error: " + ise.getMessage());
        } catch (TransactionCanceledException tce) {
            System.err.println(
                    "Transaction Canceled, implies a client issue, fix before retrying. Error: " + tce.getMessage());
        } catch (Exception ex) {
            System.err.println(
                    "An exception occurred, investigate and configure retry strategy. Error: " + ex.getMessage());
        }
        return loadedObjects;
    }

    private static void executeTransactionWrite(TransactionWriteRequest transactionWriteRequest) {
        try {
            mapper.transactionWrite(transactionWriteRequest);
        } catch (DynamoDBMappingException ddbme) {
            System.err.println("Client side error in Mapper, fix before retrying. Error: " + ddbme.getMessage());
        } catch (ResourceNotFoundException rnfe) {
            System.err.println("One of the tables was not found, verify table exists before retrying. Error: "
                    + rnfe.getMessage());
        } catch (InternalServerErrorException ise) {
            System.err.println(
                    "Internal Server Error, generally safe to retry with back-off. Error: " + ise.getMessage());
        } catch (TransactionCanceledException tce) {
            System.err.println(
                    "Transaction Canceled, implies a client issue, fix before retrying. Error: " + tce.getMessage());
        } catch (Exception ex) {
            System.err.println(
                    "An exception occurred, investigate and configure retry strategy. Error: " + ex.getMessage());
        }
    }

    @DynamoDBTable(tableName = "Thread")
    public static class Thread {
        private String forumName;
        private String subject;
        private String message;
        private String lastPostedDateTime;
        private String lastPostedBy;
        private Set<String> tags;
        private int answered;
        private int views;
        private int replies;

        // Partition key
        @DynamoDBHashKey(attributeName = "ForumName")
        public String getForumName() {
            return forumName;
        }

        public void setForumName(String forumName) {
            this.forumName = forumName;
        }

        // Sort key
        @DynamoDBRangeKey(attributeName = "Subject")
        public String getSubject() {
            return subject;
        }

        public void setSubject(String subject) {
            this.subject = subject;
        }

        @DynamoDBAttribute(attributeName = "Message")
        public String getMessage() {
            return message;
        }

        public void setMessage(String message) {
            this.message = message;
        }

        @DynamoDBAttribute(attributeName = "LastPostedDateTime")
        public String getLastPostedDateTime() {
            return lastPostedDateTime;
        }

        public void setLastPostedDateTime(String lastPostedDateTime) {
            this.lastPostedDateTime = lastPostedDateTime;
        }

        @DynamoDBAttribute(attributeName = "LastPostedBy")
        public String getLastPostedBy() {
            return lastPostedBy;
        }

        public void setLastPostedBy(String lastPostedBy) {
            this.lastPostedBy = lastPostedBy;
        }

        @DynamoDBAttribute(attributeName = "Tags")
        public Set<String> getTags() {
            return tags;
        }

        public void setTags(Set<String> tags) {
            this.tags = tags;
        }

        @DynamoDBAttribute(attributeName = "Answered")
        public int getAnswered() {
            return answered;
        }

        public void setAnswered(int answered) {
            this.answered = answered;
        }

        @DynamoDBAttribute(attributeName = "Views")
        public int getViews() {
            return views;
        }

        public void setViews(int views) {
            this.views = views;
        }

        @DynamoDBAttribute(attributeName = "Replies")
        public int getReplies() {
            return replies;
        }

        public void setReplies(int replies) {
            this.replies = replies;
        }

    }

    @DynamoDBTable(tableName = "Forum")
    public static class Forum {
        private String name;
        private String category;
        private int threads;

        // Partition key
        @DynamoDBHashKey(attributeName = "Name")
        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        @DynamoDBAttribute(attributeName = "Category")
        public String getCategory() {
            return category;
        }

        public void setCategory(String category) {
            this.category = category;
        }

        @DynamoDBAttribute(attributeName = "Threads")
        public int getThreads() {
            return threads;
        }

        public void setThreads(int threads) {
            this.threads = threads;
        }
    }
}