How to query a Dynamo DB having a GSI with only hashKeys using DynamoDBMapper

Question

I am very new to Dynamo DB and may be this is very trivial question, but i went through the documents of Dynamo DB and stack overflow questions but i couldnt find a single link which tells how to query DDB for GSI which has only hash key and there are no range key specified for the same.

I get the exception Illegal query expression: No hash key condition is found in the query.

Answer 1

On your DynamoDB annotated model object, you should use @DynamoDBIndexHashKey(globalSecondaryIndexName = "gsiIndexName) to signify that it is a hash key for the GSI:

@DynamoDBTable(tableName = "myTable") public class MyTable {     ...      @DynamoDBIndexHashKey(globalSecondaryIndexName = "myGsi")     public String getGsiHk() {         return gsiHk;     }      ... } 

And then use the query method on the DynamoDBMapper:

final MyTable gsiKeyObj = new MyTable(); gsiKeyObj.setGsiHk("myGsiHkValue"); final DynamoDBQueryExpression<MyTable> queryExpression =      new DynamoDBQueryExpression<>(); queryExpression.setHashKeyValues(gsiKeyObj); queryExpression.setIndexName("myGsi"); queryExpression.setConsistentRead(false);   // cannot use consistent read on GSI final PaginatedQueryList<MyTable> results =      mapper.query(MyTable.class, queryExpression);