How to do Query in DynamoDB on the basis of HashKey and range Key?

Question

I am new to DynamoDb stuff. I just want to know how can we query on a table in DynamoDB with the hashKey and rangeKey.

Let's say my Table is TestTable and it's schema is something like this:

1.Id (HK of type String)
2 Date (RK of type String )
3 Name (attribute of type String)

Now If I want to query on this table on the basis of hashKey which is Id here, we make a query as :

Let's say my query is to get all Items having Id ="123".

TestTable testTable = new TestTable();
testTable.setId("123");

DynamoDBQueryExpression<TestTable> queryExpression = new DynamoDBQueryExpression<TestTable>()
                                                                .withHashKeyValues(TestTable)
                                                                .withConsistentRead(false);

Now I want to get all Items having Id ="123" and Date ="1234".

How can I query this thing in DynamoDB

I am using java as my programming language.

Answer 1

I wrote an article about DynamoDB queries and indexing using the AWS Java SDK some time ago: http://labs.journwe.com/2013/12/15/dynamodb-secondary-indexes/

In your case, it should work like this (see http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/JavaQueryScanORMModelExample.html):

AmazonDynamoDBClient client = new AmazonDynamoDBClient(new ProfileCredentialsProvider());
DynamoDBMapper mapper = new DynamoDBMapper(client);

String hashKey = "123";
long twoWeeksAgoMilli = (new Date()).getTime() - (15L*24L*60L*60L*1000L);
Date twoWeeksAgo = new Date();
twoWeeksAgo.setTime(twoWeeksAgoMilli);
SimpleDateFormat dateFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
dateFormatter.setTimeZone(TimeZone.getTimeZone("UTC"));
String twoWeeksAgoStr = dateFormatter.format(twoWeeksAgo);            
Condition rangeKeyCondition = new Condition()
        .withComparisonOperator(ComparisonOperator.GT.toString())
        .withAttributeValueList(new AttributeValue().withS(twoWeeksAgoStr.toString()));

Reply replyKey = new Reply();
replyKey.setId(hashKey);

DynamoDBQueryExpression<Reply> queryExpression = new DynamoDBQueryExpression<Reply>()
        .withHashKeyValues(replyKey)
        .withRangeKeyCondition("ReplyDateTime", rangeKeyCondition);

List<Reply> latestReplies = mapper.query(Reply.class, queryExpression);

Check out the Java Object Persistence Model section of the DynamoDB docs for more info.

Answer 2

You could use dynamoDbMapper.load() as following:

TestTable testTable = new TestTable();
testTable.setId("123");
testTable.setDate("1234");
TestTable result = dynamoDBMapper.load(testTable);