Monday, 18 July 2016

Query DynamoDB Items with Java

On 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.

In case you use docker you can find a local dynamodb image or you can create one on you 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 creating the Users table using his email for a hash key. The next table will be called Logins. Logins should keep track 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 occured as a range key with can find sort the login entries or perform advanced queries based on the login date for a specific user.

However most of the times 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 Supervisor would be his name. A supervisor will work for a company. The company will be our global secondary index. Since the companies own more than one factories 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);

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);