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Create DynamoDB Tables With Java

DZone's Guide to

Create DynamoDB Tables With Java

Check out how to create tables in a DynamoDB instance using Java.

· Java Zone
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What every Java engineer should know about microservices: Reactive Microservices Architecture.  Brought to you in partnership with Lightbend.

In this post, we will create Tables on a DynamoDB Database the Java way.

Before getting started, we need to have local DynamoDB installed since we want to avoid any costs for DynamoDB usage. There was a previous post on local DynamoDB.

In case you use Docker, you can find a local DynamoDB image or you can create one on your own as described here.

The DynamoDB Java SDK gives us the ability to create DynamoDB tables using Java code.

The most basic action is to create a table with a hash key. In this case, the email of the user would be the hash key.

List<KeySchemaElement> elements = new ArrayList<KeySchemaElement>();
        KeySchemaElement keySchemaElement = new KeySchemaElement()
                .withKeyType(KeyType.HASH)
                .withAttributeName("email");
        elements.add(keySchemaElement);

        List<AttributeDefinition> attributeDefinitions = new ArrayList<>();

        attributeDefinitions.add(new AttributeDefinition()
                .withAttributeName("email")
                .withAttributeType(ScalarAttributeType.S));

        CreateTableRequest createTableRequest = new CreateTableRequest()
                .withTableName("Users")
                .withKeySchema(elements)
                .withProvisionedThroughput(new ProvisionedThroughput()
                        .withReadCapacityUnits(5L)
                        .withWriteCapacityUnits(5L))
                .withAttributeDefinitions(attributeDefinitions);

        amazonDynamoDB.createTable(createTableRequest);   

What we did is create the Users table using his email for a hash key.

The next table will be called Logins. Logins should keep track of each time the user logged in. To do so, apart from using a hash key, we will also use a range key.

        List<KeySchemaElement> elements = new ArrayList<KeySchemaElement>();
        KeySchemaElement hashKey = new KeySchemaElement()
                .withKeyType(KeyType.HASH)
                .withAttributeName("email");
        KeySchemaElement rangeKey = new KeySchemaElement()
                .withKeyType(KeyType.RANGE)
                .withAttributeName("timestamp");
        elements.add(hashKey);
        elements.add(rangeKey);


        List<AttributeDefinition> attributeDefinitions = new ArrayList<>();

        attributeDefinitions.add(new AttributeDefinition()
                .withAttributeName("email")
                .withAttributeType(ScalarAttributeType.S));


        attributeDefinitions.add(new AttributeDefinition()
                .withAttributeName("timestamp")
                .withAttributeType(ScalarAttributeType.N));

        CreateTableRequest createTableRequest = new CreateTableRequest()
                .withTableName("Logins")
                .withKeySchema(elements)
                .withProvisionedThroughput(new ProvisionedThroughput()
                        .withReadCapacityUnits(5L)
                        .withWriteCapacityUnits(5L))
                .withAttributeDefinitions(attributeDefinitions);


        amazonDynamoDB.createTable(createTableRequest);

By using the email as a hash key we can query for the logins of the specific user. By using the date that the login occurred as a range key we can find and sort the login entries or perform advanced queries based on the login date for a specific user.

However, most of the time a hash key and range key are not enough for our needs. DynamoDB provides us with Global Secondary indexes and Local secondary Indexes.

We will create the table Supervisors. The hash key of a Supervisor would be his name. A supervisor will work in a company. The company will be our global secondary index. Since the companies own more than one factory, the field factory would be the range key.

List<KeySchemaElement> elements = new ArrayList<>();
        KeySchemaElement hashKey = new KeySchemaElement()
                .withKeyType(KeyType.HASH)
                .withAttributeName("name");
        elements.add(hashKey);

        List<GlobalSecondaryIndex> globalSecondaryIndices = new ArrayList<>();

        ArrayList<KeySchemaElement> indexKeySchema = new ArrayList<>();

        indexKeySchema.add(new KeySchemaElement()
                .withAttributeName("company")
                .withKeyType(KeyType.HASH));  //Partition key
        indexKeySchema.add(new KeySchemaElement()
                .withAttributeName("factory")
                .withKeyType(KeyType.RANGE));  //Sort key


        GlobalSecondaryIndex factoryIndex = new GlobalSecondaryIndex()
                .withIndexName("FactoryIndex")
                .withProvisionedThroughput(new ProvisionedThroughput()
                        .withReadCapacityUnits((long) 10)
                        .withWriteCapacityUnits((long) 1))
                .withKeySchema(indexKeySchema)
                .withProjection(new Projection().withProjectionType(ProjectionType.ALL));
        globalSecondaryIndices.add(factoryIndex);

        List<AttributeDefinition> attributeDefinitions = new ArrayList<>();

        attributeDefinitions.add(new AttributeDefinition()
                .withAttributeName("name")
                .withAttributeType(ScalarAttributeType.S));
        attributeDefinitions.add(new AttributeDefinition()
                .withAttributeName("company")
                .withAttributeType(ScalarAttributeType.S));
        attributeDefinitions.add(new AttributeDefinition()
                .withAttributeName("factory")
                .withAttributeType(ScalarAttributeType.S));

        CreateTableRequest createTableRequest = new CreateTableRequest()
                .withTableName("Supervisors")
                .withKeySchema(elements)
                .withProvisionedThroughput(new ProvisionedThroughput()
                        .withReadCapacityUnits(5L)
                        .withWriteCapacityUnits(5L))
                .withGlobalSecondaryIndexes(factoryIndex)
                .withAttributeDefinitions(attributeDefinitions);

        amazonDynamoDB.createTable(createTableRequest);

The next table would be the table Companies. The hash key would be the parent company and the range key the subsidiary company. Each company has a CEO. The CEO would be the range key for the local secondary index.

List<KeySchemaElement> elements = new ArrayList<>();
        KeySchemaElement hashKey = new KeySchemaElement()
                .withKeyType(KeyType.HASH)
                .withAttributeName("name");
        KeySchemaElement rangeKey = new KeySchemaElement()
                .withKeyType(KeyType.RANGE)
                .withAttributeName("subsidiary");

        elements.add(hashKey);
        elements.add(rangeKey);

        List<LocalSecondaryIndex> localSecondaryIndices = new ArrayList<>();

        ArrayList<KeySchemaElement> indexKeySchema = new ArrayList<>();

        indexKeySchema.add(new KeySchemaElement()
                .withAttributeName("name")
                .withKeyType(KeyType.HASH));
        indexKeySchema.add(new KeySchemaElement()
                .withAttributeName("ceo")
                .withKeyType(KeyType.RANGE));

        LocalSecondaryIndex ceoIndex = new LocalSecondaryIndex()
                .withIndexName("CeoIndex")
                .withKeySchema(indexKeySchema)
                .withProjection(new Projection().withProjectionType(ProjectionType.ALL));
        localSecondaryIndices.add(ceoIndex);

        List<AttributeDefinition> attributeDefinitions = new ArrayList<>();

        attributeDefinitions.add(new AttributeDefinition()
                .withAttributeName("name")
                .withAttributeType(ScalarAttributeType.S));
        attributeDefinitions.add(new AttributeDefinition()
                .withAttributeName("subsidiary")
                .withAttributeType(ScalarAttributeType.S));
        attributeDefinitions.add(new AttributeDefinition()
                .withAttributeName("ceo")
                .withAttributeType(ScalarAttributeType.S));

        CreateTableRequest createTableRequest = new CreateTableRequest()
                .withTableName("Companies")
                .withKeySchema(elements)
                .withProvisionedThroughput(new ProvisionedThroughput()
                        .withReadCapacityUnits(5L)
                        .withWriteCapacityUnits(5L))
                .withLocalSecondaryIndexes(localSecondaryIndices)
                .withAttributeDefinitions(attributeDefinitions);

        amazonDynamoDB.createTable(createTableRequest);

You can find the source code on GitHub.

Microservices for Java, explained. Revitalize your legacy systems (and your career) with Reactive Microservices Architecture, a free O'Reilly book. Brought to you in partnership with Lightbend.

Topics:
hash ,key ,local ,dynamodb ,java ,tables ,code

Published at DZone with permission of Emmanouil Gkatziouras, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

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