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Amazon DynamoDB
Developer Guide (API Version 2012-08-10)

Working with Global Secondary Indexes: Java

You can use the AWS SDK for Java Document API to create a table with one or more global secondary indexes, describe the indexes on the table and perform queries using the indexes.

The following are the common steps for table operations.

  1. Create an instance of the DynamoDB class.

  2. Provide the required and optional parameters for the operation by creating the corresponding request objects.

  3. Call the appropriate method provided by the client that you created in the preceding step.

Create a Table With a Global Secondary Index

You can create global secondary indexes at the same time that you create a table. To do this, use CreateTable and provide your specifications for one or more global secondary indexes. The following Java code snippet creates a table to hold information about weather data. The partition key is Location and the sort key is Date. A global secondary index named PrecipIndex allows fast access to precipitation data for various locations.

The following are the steps to create a table with a global secondary index, using the DynamoDB document API.

  1. Create an instance of the DynamoDB class.

  2. Create an instance of the CreateTableRequest class to provide the request information.

    You must provide the table name, its primary key, and the provisioned throughput values. For the global secondary index, you must provide the index name, its provisioned throughput settings, the attribute definitions for the index sort key, the key schema for the index, and the attribute projection.

  3. Call the createTable method by providing the request object as a parameter.

The following Java code snippet demonstrates the preceding steps. The snippet creates a table (WeatherData) with a global secondary index (PrecipIndex). The index partition key is Date and its sort key is Precipitation. All of the table attributes are projected into the index. Users can query this index to obtain weather data for a particular date, optionally sorting the data by precipitation amount.

Note that since Precipitation is not a key attribute for the table, it is not required; however, WeatherData items without Precipitation will not appear in PrecipIndex.


DynamoDB dynamoDB = new DynamoDB(new AmazonDynamoDBClient(
			new ProfileCredentialsProvider()));

// Attribute definitions
ArrayList<AttributeDefinition> attributeDefinitions = new ArrayList<AttributeDefinition>();

attributeDefinitions.add(new AttributeDefinition()
    .withAttributeName("Location")
    .withAttributeType("S"));
attributeDefinitions.add(new AttributeDefinition()
    .withAttributeName("Date")
    .withAttributeType("S"));
attributeDefinitions.add(new AttributeDefinition()
    .withAttributeName("Precipitation")
    .withAttributeType("N"));

// Table key schema
ArrayList<KeySchemaElement> tableKeySchema = new ArrayList<KeySchemaElement>();
tableKeySchema.add(new KeySchemaElement()
    .withAttributeName("Location")
    .withKeyType(KeyType.HASH));  //Partition key
tableKeySchema.add(new KeySchemaElement()
    .withAttributeName("Date")
    .withKeyType(KeyType.RANGE));  //Sort key

// PrecipIndex
GlobalSecondaryIndex precipIndex = new GlobalSecondaryIndex()
    .withIndexName("PrecipIndex")
    .withProvisionedThroughput(new ProvisionedThroughput()
        .withReadCapacityUnits((long) 10)
        .withWriteCapacityUnits((long) 1))
        .withProjection(new Projection().withProjectionType(ProjectionType.ALL));

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

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

precipIndex.setKeySchema(indexKeySchema);

CreateTableRequest createTableRequest = new CreateTableRequest()
    .withTableName("WeatherData")
    .withProvisionedThroughput(new ProvisionedThroughput()
        .withReadCapacityUnits((long) 5)
        .withWriteCapacityUnits((long) 1))
    .withAttributeDefinitions(attributeDefinitions)
    .withKeySchema(tableKeySchema)
    .withGlobalSecondaryIndexes(precipIndex);

Table table = dynamoDB.createTable(createTableRequest);
System.out.println(table.getDescription());

You must wait until DynamoDB creates the table and sets the table status to ACTIVE. After that, you can begin putting data items into the table.

Describe a Table With a Global Secondary Index

To get information about global secondary indexes on a table, use DescribeTable. For each index, you can access its name, key schema, and projected attributes.

The following are the steps to access global secondary index information a table.

  1. Create an instance of the DynamoDB class.

  2. Create an instance of the Table class to represent the index you want to work with.

  3. Call the describe method on the Table object.

The following Java code snippet demonstrates the preceding steps.


DynamoDB dynamoDB = new DynamoDB(new AmazonDynamoDBClient(
    new ProfileCredentialsProvider()));

Table table = dynamoDB.getTable("WeatherData");
TableDescription tableDesc = table.describe();
	

Iterator<GlobalSecondaryIndexDescription> gsiIter = tableDesc.getGlobalSecondaryIndexes().iterator();
while (gsiIter.hasNext()) {
    GlobalSecondaryIndexDescription gsiDesc = gsiIter.next();
    System.out.println("Info for index "
         + gsiDesc.getIndexName() + ":");

    Iterator<KeySchemaElement> kseIter = gsiDesc.getKeySchema().iterator();
    while (kseIter.hasNext()) {
        KeySchemaElement kse = kseIter.next();
        System.out.printf("\t%s: %s\n", kse.getAttributeName(), kse.getKeyType());
    }
    Projection projection = gsiDesc.getProjection();
    System.out.println("\tThe projection type is: "
        + projection.getProjectionType());
    if (projection.getProjectionType().toString().equals("INCLUDE")) {
        System.out.println("\t\tThe non-key projected attributes are: "
            + projection.getNonKeyAttributes());
    }
}

Query a Global Secondary Index

You can use Query on a global secondary index, in much the same way you Query a table. You need to specify the index name, the query criteria for the index partition key and sort key (if present), and the attributes that you want to return. In this example, the index is PrecipIndex, which has a partition key of Date and a sort key of Precipitation. The index query returns all of the weather data for a particular date, where the precipitation is greater than zero.

The following are the steps to query a global secondary index using the AWS SDK for Java Document API.

  1. Create an instance of the DynamoDB class.

  2. Create an instance of the Table class to represent the index you want to work with.

  3. Create an instance of the Index class for the index you want to query.

  4. Call the query method on the Index object.

The attribute name Date is a DynamoDB reserved word. Therefore, we must use an expression attribute name as a placeholder in the KeyConditionExpression.

The following Java code snippet demonstrates the preceding steps.


DynamoDB dynamoDB = new DynamoDB(new AmazonDynamoDBClient(
    new ProfileCredentialsProvider()));

Table table = dynamoDB.getTable("WeatherData");
Index index = table.getIndex("PrecipIndex");

QuerySpec spec = new QuerySpec()
    .withKeyConditionExpression("#d = :v_date and Precipitation = :v_precip")
    .withNameMap(new NameMap()
        .with("#d", "Date"))
    .withValueMap(new ValueMap()
        .withString(":v_date","2013-08-10")
        .withNumber(":v_precip",0));

ItemCollection<QueryOutcome> items = index.query(spec);
Iterator<Item> iter = items.iterator(); 
while (iter.hasNext()) {
    System.out.println(iter.next().toJSONPretty());
}